NASA’s Beyond Einstein Program: An Architecture for Implementation Comments submitted via email to the committee

John Middleditch, LNL, 12/5/06 “Decision on Beyond Einstein” Dear Colleagues, First, apologies for those of you I could not e-mail directly (and others who wish I hadn't!).  Time is short, hence the urgency.  As a concerned citizen scientist I feel it is my duty to point out a few facts relating to JDEM/SNAP (you may use astro-ph/0608386 for reference -- you can just imagine the time I've had getting this past the ApJL editor!). You should (and many of you may already)  be aware of two recent developments which cast considerable doubt on the accepted paradigm of a single accreting white dwarf star, upon which cosmology determined from Type Ia supernovae depends. The most recent development (~5 Nov06) was SN 2006mr in NGC 1316, the FOURTH Type Ia SN in the past 26 years!  NGC 1316 is an elliptical galaxy with dust lanes, commonly accepted as a collision of that elliptical with a spiral. The less recent is the realization that SN 2003fg produced 1.2 solar masses of 56Ni (Howell et al. 2006, Nature, 443, 308). Together, these developments mean that Type Ia SNe are produced by white dwarf-white dwarf merger-induced core-collapse (however, thermonuclear burn also happens), instead of from a single, slowly accreting white dwarf.  (A number of other sound objections to the single WD paradigm are listed in astro-ph/0608386). Why is this a problem for Ia cosmology? Because Ia's should look like pictures of the axial explosion of SN 1987A, only worse in that the velocity of the polar ejecta is much higher than in 87A (which had H and He mixed with the  C & O). So what?  Doesn't the thermonuclear equatorial ball dominate the luminosity of these?  Yes, but for Ia's viewed off the merger equator, the shadow of the high velocity polar ejecta of many Ia's will evaporate and expose a part of that ball just when \Delta m{15} is being measured.  The result is that the drop in luminosity (the width-luminosity correction) is less than it ought to be, and the result is a corrected Ia which is too faint for its redshift.  Proponents will point out that the Ia's are too faint, even without the WL correction.  Maybe so, or not, depending on the completeness of the local sample, which takes time to improve, especially in the light of 2003fg.  In any case, Ia's aren't what they were advertised to be, even though SNAP's measurements will hardly be bothered by the embedded, weakly-magnetized, rapidly spinning pulsars, let alone be able to detect any trace of their signature.  But they will be bothered by the other problems. So what is the point of this msg? It is that you should go into the decision between JDEM/SNAP, LISA, and CONEX with your EYES OPEN.  If we can't afford LISA or CONEX, then be aware that JDEM/SNAP may not produce the miracles it's advertised. Nevertheless, it will do something, and a hundred astronomers may slit their wrists if it doesn't get chosen, flawed as the science may be. I wish I knew how to fix JDEM/SNAP, but I don't.  It may be that further ongoing study of local Ia's could enable us to make sense of the data that it will produce if it flies.  The prudent thing would be to wait a decade, while astronomers deal with the last few months' revelations, but prudence may be cold comfort to those who have been promised career tracks which depend on it.  Eventually, we'll get around to finding the millisecond pulsars lurking within these that have to be there, and even pulsing optically for a while (see astro-ph/0010044, 2000, New Astronomy, 5, 243, 2004, ApJL, 601, L167, in addtion to astro-ph/0608386). Now that I've told you about all of this, let me just say that I don't envy your position. Yours sincerely,  -John Middleditch

William Carithers, Lawrence Berkeley Lab, 2/1/07 “BEPAC Recommendation” I hope that the main finding of the Panel is that ALL of the Beyond Einstein missions address the most fundamental and critical issues in physics, astrophysics, and cosmology. Take away even one and science is diminished. I fear that the charge of picking the first mission for launch is a form of “Sophie¹s choice” whereby one mission will live and, given the current budgetary environment, the others will die. I urge you to avoid this form of choice by making your main recommendation that the entire Beyond Einstein program be given highest priority within NASA¹s Science Mission Directorate. Still, you must satisfy your charge and choose the first. You will certainly develop your own criteria which consider both scientific impact and technical readiness. I hope you will lead with the science. I believe that discovering the nature of Dark Energy is the most pressing scientific problem facing us and several panels agree. The Dark Energy Task Forces said it very well: ³Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science.² If none of the JDEM missions were technically ready, you would have a hard choice indeed. Fortunately, that is not the case. Because of a five year DOE-funded R&D program, the SNAP mission has advanced to a very high level of technical readiness and could start construction even before 2009. The confluence of highest scientific merit, advanced technical readiness, and reasonable costs argue very strongly that JDEM be the first Beyond Einstein to be launched. I wish you wisdom in this challenging task and thank you for taking it on. Respectfully, Bill Carithers

Richard Ellis, Professor of Astronomy at Caltech, 2/1/07 “5 minute statement made on February 1st 2007 at Beyond Einstein Program Town Hall Meeting, Newport Beach by Richard Ellis (Caltech)” I'm Richard Ellis. I'm a professor at Caltech and an observational cosmologist. I have been involved in the study of distant supernovae since 1985. I was a member of the team that found the first supernova at moderate redshift in 1987 and was on Saul Perlmutter's team at the time when dark energy was discovered in 1998 I have also been involved in weak lensing. My team was one of four that detected weak lensing from large scale structure in 2000 and I am a co-author on the recent Nature paper (18 January 2007) which revealed, for the first time, the topology of the dark matter distribution. I was initially UK PI of the AAT 2 degree field redshift survey which discovered baryon oscillations in the local galaxy distribution, and am currently PI of a proposal to build a second generation multi-object spectrograph, WFMOS, for the Japanese Subaru telescope, to extend this method to a redshift of 1 to provide a precise constraint on dark energy. So I am working in all 3 of the most promising probes on dark energy, using both ground- and space-based facilities. In addition to lending my strong support to the rationale for making precise measures of dark energy via JDEM, I want to use this occasion to give my judgements on which aspects can and cannot be effectively accomplished from the ground. I see this is a key issue in the committee's deliberations and welcome the opportunity to make a few statements. I want to stress that these are my own personal views and do not represent a statement made on behalf of any of the proposing JDEM teams. Supernova are individual explosions in galaxies and their properties are now known to vary from galaxy to galaxy according to the age of the stellar population. I have spent the past 4 years studying a representative sample of distant supernovae in great detail at the Keck observatory. In my opinion, it is not yet clear whether the dispersion in properties that we are finding among supernovae can be removed by empirical correlations to the precision necessary for very accurate constraints on dark energy. This is not a concern with the current surveys but it could well be for the proposed future ones. We will certainly achieve better measurement precision from space than from the ground, but the question of whether we will hit some systematic floor is as yet undetermined. I conclude therefore that while it is beneficial to go to space to study supernovae, one should be careful to have at least one further method for studying dark energy. Baryon oscillation probes require very ambitious redshift surveys. It is not practical to substitute photometric redshifts for precision work; so one needs to build a powerful multi-object spectrograph. The gain of undertaking such a survey at high redshift (z~2-3) c.f. moderate redshift (z~1) is not great unless, for some reason, dark energy is very rapidly changing. In my opinion redshifts can be measured at moderate redshift in abundance more cost-effectively from the ground. The instrument I am designing for the Japanese Subaru telescope is likely to cost $40-50M and in only a few hundred nights of observing time, it will be very effective in constraining dark energy, providing a ten-fold improvement in the dark energy task force figure of merit compared to current experiments. One could certainly do the same faster in space, particularly at a higher redshift, but I don't find this a compelling reason to go into space. I conclude, therefore, that baryon oscillations should be done at z~1 from the ground first and the results analyzed before contemplating a space mission whose main thrust is spectroscopy. Weak lensing relies on the subtly-distorted shapes of millions of faint galaxies. There is no question from the achievements of the above-cited Nature paper that these small effects are much more carefully studied from space. One needs to measure both the absolute distortion as well as to survey the distant universe in a uniform manner. It's simply not possible to achieve the required uniformity of image quality or calibrate the absolute distortions with a ground based telescope. It was apparently pointed out by a skeptic on your panel on Tuesday that even with Hubble Space Telescope this is still a challenge. I completely agree. But the limitations of Hubble are instrumental rather than fundamental to the method. We can learn from this experience and what we have found certainly does not detract from the argument of going into space. The progress in this field is truly incredible. Weak lensing was only detected in 2000 and yet here in 2007, we have remarkable 3-D maps of the dark matter revealed via this technique. I'm reminded of the phenomenal progress in microwave background studies in the 1980s which, of course, led ultimately to the Nobel Prize. As an aside, a talented new generation of observational cosmologists have entered the weak lensing field. You won't find many at such a town hall meeting but at a conference last summer when asked how to proceed the answer was clear - a space mission is required to realize the full potential of this remarkable phenomenon of General Relativity. In conclusion, the mystery of dark energy is the ultimate scientific adventure. Whatever the outcome, it will fundamentally change our view of the Universe. Weak lensing is the most promising method but can only achieve the precision necessary in space. Supernovae are likewise a promising tool whose photometric precision will be superior in space but, as a tool, they are in my view insufficient by themselves. A space mission that is sculpted around weak lensing and supernovae should be a high priority for the scientific community.

Jeffrey McClintock, Senior Astrophysicist, Harvard-Smithsonian Center for Astrophysics, High Energy Astrophysics Division, 2/13/07 “Cambridge Town Hall Meeting / open mike statement” I am presently a Smithsonian Senior Astrophysicist at CfA and an X-ray observer since the 1960s. For 25 years, I have been studying stellar black holes and measuring their masses. During the past two years, our team has been obtaining the first plausibly-reliable estimates of spin for a few of these black holes, and this is the most exciting work I have ever done. We estimate the spin of a black hole by fitting its 1-10 keV continuum spectrum, with distance and black-hole mass supplied as inputs from ground-based observations. Our goal within the next few years is to measure the masses of a dozen stellar black holes. At the moment, we are focused on the first and the only-known eclipsing black hole, M33 X-7, which was discovered by Chandra. The system lies at a distance of 800 kpc, which is 100 times the distance of a typical Galactic black hole. With Gemini North, we have obtained a precise black hole mass, and with Chandra we are in the process of obtaining a very high quality estimate of the black hole's spin. As you heard from Steve Murray yesterday, there are a thousand committed X-ray observers like myself, and another thousand plus optical, radio, and other observers who rely on Chandra and Suzaku presently. All of us eagerly await the launch of Constellation-X. I am excited about Constellation-X because it will open wide the second great avenue for determining the spins of black holes, namely, modeling both the static and the dynamic profile of the Fe line. Of course, this is already the focal research topic of many dozens of X-ray astronomers. I am working eagerly now with yesterday's speaker Julia Lee to learn how I too can contribute to the study of the Fe line. But what Constellation-X will in fact achieve for the study of black holes cannot be imagined. For example, when plans were laid for Chandra, no one could foresee that it would enable the discovery -- as well as the complete characterization -- of the first eclipsing black hole, nor could one anticipate the multitude of other astonishing discoveries made possible by this Great Observatory. And likewise, no one can anticipate where Constellation-X will take us as we enter the age of X-ray spectroscopy. Thank you for your efforts in examining the Beyond Einstein missions, sincerely, Jeffrey McClintock

Kathryn Flanagan, Principal Research Scientist, Kavli Institute for Astrophysics and Space Research, MIT, 2/16/07 “Text of my 5 minutes presentation to BEPAC on February 12” My name is Kathryn Flanagan. I am a Principal Research Scientist at MIT’s Kavli Institute for Astrophysics and Space Research. About 4 years ago I took on a role as Integrated Product Team Lead for the Reflection Grating Spectrometer. This role ended more than a year ago. I do not currently receive funding from Constellation-X but I remain a part of its Facility Science Team. I have served in various NASA committees and roadmapping efforts, including co-chair of a strategic roadmap. I know how important and challenging this process can be, and I thank you for this service to our community. I have three points that I would like to make today: I wish to remind you of the science Constellation-X will enable in its role as a Great Observatory. I wish to describe for you my observations, from the “trenches”, of technology development on Constellation-X and its impact in our university environment. And I would like to describe my experience that the community supporting Constellation-X is passionately committed. GREAT OBSERVATORY SCIENCE: The focus of much of the presentations to you has been “What great questions will this mission answer?” But I call to your attention the role of Constellation-X as a great observatory. You already know what Con-X will tell us about Black holes, Dark Energy, the WHIM and neutron stars. What about the rest of astronomy in the X-ray band? I myself study supernova remnants. These lovely objects are the remains of a massive star exploding at the end of its life. (Julia Lee talked to you about dust to dust- I am arguing for ashes-to-ashes!) This process creates and disperses elements through the universe. A supernova remnant can be detected in visible, infrared and ultraviolet, but only a few percent of the ejected matter is sampled this way. Most of its radiation is the form of radio and X-rays. The radio band samples the free electrons that have been ionized from the atoms. But to understand the elements themselves, constituting the bulk of ejecta, and thus driving the dynamics of the remnant, we must study the x-ray lines. This requires the high-resolution spectral capability of Con-X. With it, we can examine the abundance of the elements, their temperature and ionization age, the velocity structure. We can get at the physics of the remnant, and through it a hint of the physics of the explosion itself. X-rays cannot be observed from the ground: this science cannot be done without an X-ray observatory such as Constellation-X. Other science enabled by Constellation-X include stars, galactic superwinds, magnetars, AGN jets and comets – the rest of astronomy that wasn’t entered in the beauty pageant. There are many experts in the audience, and I encourage them to contribute during the open mike period. TECHNOLOGY DEVELOPMENT:  Now let me speak about technology development for the grating spectrometer on Constellation-X. To make my remarks concrete, I will focus on one particular lab and particular individuals at MIT, and I apologize upfront for neglecting the others. If you check with Fiona Harrison on your committee, who led the High Energy X-ray Telescope Team’s technology development, I think you will find my comments apply in a general way to other technology development groups. Early on, we knew Con-X would need big, thin, highly efficient reflection gratings that could be mass-produced. They needed to be extremely flat, and mounted to high precision – a substantially challenge when you intend to use extremely thin gratings. The Space Nanotechnology Laboratory and MIT exploited the crystal planes of silicon to create the most efficient X-ray reflection grating ever produced. It made them of large size (300mm diameter), and four times thinner than those that flew on XMM-Newton. The head of this lab, Mark Schattenburg, invented the nanoruler – a machine capable of producing a master grating in minutes. Contrast this with diamond ruling, which takes weeks. This machine is easily configurable, allowing us to tailor many different masters easily. In fact, it was selected as one of the top 100 inventions in 2004. Then they confirmed a suitable method (nanoimprint lithography) to mass produce replica gratings from the masters. This left the question of mounting and flatness. As part of her research, a student in the lab polished the world’s flattest wafer. In order to measure its flatness, she had to invent a force-free holder, which was found to be comparable to the best metrology available. Her next task – her last one – effectively pushed forward the technology on two fronts: she came up with a technique for mounting and aligning the gratings, and in the process created a cheap accessible way to flatten them. This last achievement held great promise for creating future high resolution X-ray optics that are light and cheap - a direction we need to go for our vision missions. In July of last year, we were informed that the Con-X grating technology development would be terminated. The student was abruptly removed from this incredible development path, and was required to change her thesis research topic - an incalculable loss for her, a much greater one for Constellation-X. A couple of months later, word came down that Con-X was contemplating a “science enhancement package” and encouraged white papers on instruments that were even lighter, cheaper and better. In response, this same team invented, literally, a new type of grating. It would exhibit the super-efficiency expected of the best reflection grating, but would be significantly lighter, two orders of magnitude easier to align, and fabricable directly in house. Calculations showed that a 200ks Chandra grating observation could be accomplished with this instrument in 2 ks on Constellation-X. To round out the picture, in a move I now think of typical from this lab, another strudent actually fabricated a prototype. It will be X-ray tested in the next few months. Spinoffs: Work on the Chandra x-ray transmission grating spectrometer in the early 1980s led to the invention by MIT researchers of a particular type of lithography mask called the halftone phase-shift mask. This mask is used to fabricate leading-edge computer chips because it allows higher resolution imaging. Today it has been licensed to most chip makers worldwide and has a 98% market share of masks used to fabricate the critical levels of computer chips. Virtually every computer made today uses this technology. To my mind, this is one representative example of NASA at its best – small investments in technology development can train our next generation of instrumentalists, create remarkable breakthroughs, and generates spinoffs that aid the country and indeed the world. This example also represents the damage created by the instability and erratic commitment that has been the outcome of recent budget troubles. The X-ray astronomy community is on the brink of losing a generation of instrumentalists. Indeed, this remarkable lab is potentially months – not years – away from extinction. COMMITMENT OF THE COMMUNITY: I would like to end by remarking on my experience of this community’s commitment to Con-X. When I started out my new “management” role as IPT lead for the grating spectrometer, I quickly learned that there is a big difference between talking and doing. I am awed by the willingness of this community to step up to the plate. The first 3 months in that role, I had 25 people from 6 institutions volunteering their time to take on the challenge of modeling gratings. Participants were from industry, government, and several universities. In the last few months, in developing the white paper, I can say I experienced the same thing. I am convinced that this community is eager to do great things – and will be the cradle of our vision missions. Give us the ball – we will run with it. Kathryn Flanagan Principal Research Scientist MIT Kavli Institute for Astrophysics and Space Research

Smita Mathur, Associate Professor, Astronomy Department, Ohio State University, 2/23/07 “To the Beyond Einstein Program Assessment Committee” Dear Committee, I'm writing this letter in support of the Constellation-X mission in the Beyond Einstein program. I find it to be scientifically compelling, technologically possible, and inherently a space mission. Let me fist discuss the scientific merits of the Constellation-X mission. Because of the down-scoping of the original AXAF mission, the Chandra X-ray Observatory is mainly an imaging facility. There are two transmission gratings on Chandra, but their combination of resolution and effective area are limiting. Nonetheless, these grating observations have given us the proof of concept to go ahead with a more ambitious spectroscopic mission such as Constellation-X. The Chandra observations have given us glimpses into a wide range of astrophysical scenarios. The tantalizing discoveries that I am most aware of are about (1) the warm-hot inter-galactic medium (WHIM), and (2) the winds from active galactic nuclei. The first is directly related to the cosmological ``missing baryon'' problem and the second is most significant to understand the ``feedback'' mechanism which controls the formation of disk galaxies, structure of gas in clusters of galaxies, metal and energy input in the inter-galactic medium, etc. As far as these spectroscopic observations are concerned, we are still at the discovery stage (and sometimes at a tentative discovery stage) with Chandra and to move forward to actually do astrophysical research, we need Constellation-X. From what I have read about the Constellation-X mission, I also understand that there are no major technological hurdles to overcome to accomplish this mission. This makes Constellation-X extremely attractive as it can transform a dream into reality. Thus, from the points of scientific impact, proof-of-concept, and the technological readiness, I find Constellation-X to be superior to other missions in the Beyond Einstein Program. For example, we still do not have a single detection of astronomical gravitational waves. Space based laser interferometry does not have any technological inheritance as well. While it would be wonderful to open a new window of gravitational wave astronomy, I do not think LISA is a way to go for it. Another important point to note is that there is no other way to do Constellation-X science without Constellation-X (i.e. the concept of Constellation-X by any other name). For this reason Constellation-X stands out from JDEM missions. Understanding dark energy is doubtless an important science goal, but there are several other programs designed for this purpose which are either on-going or operate on a near-term or long-term basis. Just to name a few, Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST) are ground based programs. They involve techniques such as supernova distances, strong and weak lensing, and baryon acoustic oscillations. There are S-Z surveys which give complementary information. There are HST programs on supernova searches. Even large programs on Chandra will attempt to constrain dark energy parameters using two different techniques involving X-ray clusters. Undoubtedly, the combination of all these efforts will lead to major advances in our understanding of the dark energy. The present JDEM missions are in a way parallel to these, other programs. Ideally, they should be a step forward, achieving breakthroughs which could not be achieved in any other way. It is quite possible that when we have results from all these other dark energy programs, we will be asking totally different questions, and not ``what is the value of w?'' and ``how does it evolve with redshift?''. Then the new mission concepts will have to depend upon the new questions that will emerge. It appears premature to go for space based missions such as JDEM before we have the results from all these program, and before we know exactly what we really need to know from space missions. I have mentioned only two examples of Constellation-X science that will have high impact. I have no doubt that you have heard of several other areas, e.g. strong gravity around black holes, where Constellation-X observations will provide a major break-through. The point I am trying to make is that we are practically guaranteed of scientific success of Constellation-X. Moreover, it needs to be a space mission and is feasible. The combination of all of these facts makes Constellation-X the most attractive mission in the Beyond Einstein program. Thank you very much for doing this very difficult task of choosing one of the five scientifically exciting missions! Yours sincerely, Smita Mathur Associate Professor Astronomy Department The Ohio State University.

Eric Linder, Research Professor, Space Science Laboratory, University of California, Berkeley, 3/05/07 “5 minute statement made on 1 February 2007 at Beyond Einstein Program Town Hall Meeting #1” BEPAC suggested four questions for comment, and I will address each of them. What are the most valuable science opportunities of the Beyond Einstein program? The Beyond Einstein program can test the rich variety of Einstein physics, physics that revolutionized the 20th century. This includes the cosmological constant, with its intriguing relations to both gravitational and high energy physics, Einstein's general relativity itself, and the cosmic expansion and growth histories, seeking to understand what makes up the universe, how it behaves, and what is the fate of the universe. All of these are tremendously engaging, compelling, and exciting questions. On the more astronomical side, a wide field imaging space telescope will provide opportunities for exploration and discovery as the Hubble Deep Field did -- literally a million times over. And that is perhaps the most valuable science opportunity, going after the most unknown physics, such as the 95% of the universe that is the dark side, and being open to the unknown. What we can expect to learn is the unexpected, with fundamental surprises. Dark energy is such a compelling subject for transformational science because it fills and dominates the universe; it is not just a "one part in 10^x" occurrence or effect, or existing only in extreme corners of the universe. What are the long-term goals for the science, beyond the mission projects; are we opening a new field or resolving existing questions? No matter what the answer is to the acceleration of the universe, it will be new science, rewriting physics textbooks at a basic level. We are at ground floor of our understanding now, and don't know how deep or far up the physics will lead us. This is definitely an exciting prospect. To what degree can ground-based or existing space-based capabilities solve some of these questions? The greatest risk is the risk of ending up with a ``maybe'' answer - data that may be interpreted one way or maybe another, or data that does not convince the community through its cleanness and robustness. The Dark Energy Task Force focused on the risk of systematics, and said that space-based measurements are in this sense the lower risk option. Space gives much greater leverage through the increased redshift range for calibrated candle measurements and weak lensing shape measurements. Crucially, space gives drastic improvements in systematics control for both distance measurements and growth history measurements. What is the degree of precision needed from the measurements to move the science forward? Inspired by our JDEM Science Definition Team conversations, Robert Caldwell and I derived a relative answer: to distinguish the two broad classes of physics approaching cosmological constant behavior and departing from such behavior, one requires a precision on the time variation of the equation of state ratio \sigma(w')~2(1+w). Moreover, it is clear that each technique for probing dark energy must stand on its own and that a patchwork of different instruments to make the measurement gives a dangerous opening to systematic uncertainty. Since the physical origin, and not just the phenomenology, of the cosmic acceleration is crucial, we need independent tests of the expansion history (e.g. supernova distances) and cosmic growth history (e.g. weak gravitational lensing) to identify whether the new physics arises from a new component or a new law of gravity. The reward for these challenging experiments is the extraordinary science reach - precisely the Beyond Einstein questions: what powered the Big Bang, what is the nature of gravity or extra dimensions, and what is the nature of dark energy, the overwhelming dominant component of the universe we live in.

Charles Baltay, Professor of Physics and Astronomy, Yale University, 3/15/07 “Comments to the Beyond Einstein Program Assessment Committee at the Boston Meeting” Let me start by saying that you have a very difficult choice ahead of you. All five of the Beyond Einstein probes are wonderful science, at the cutting edge of their fields, and I hope that all of them will be eventually carried out. I am a member of the SNAP collaboration and would like to make a few comments on why the JDEM mission should be chosen to proceed as soon as possible. I believe that most people agree that discovering the nature of Dark Energy is the grandest and most pressing issue facing us today. One way or another the explanation of the accelerating expansion of our universe will lead to a revolution in our understanding of the most basic issues in science. A space mission is essential for these studies. The two most mature and well understood ways to study dark energy is via Type Ia Supernovae and Weak Gravitational Lensing. With Type Ia Supernovae it is essential to go to redshifts of 1.5 or slightly higher to look far enough back in cosmic time to distinguish between competing theoretical models. At these redshifts the Supernova light is redshifted into the infrared and thus these observations can not be carried out well from the ground. In the case of weak lensing one looks at distortions of galaxy shapes comparable to or smaller than the distortions of the images due to the atmosphere, so that space observations are a huge systematic advantage. The SNAP mission has carried out a five year R&D program and is ready to move on to the construction phase as soon as funding allows. In part due to this R&D the cost of the JDEM mission is, by the standard of space missions, modest. I believe that the combination of the highest scientific merit, the technical readiness, and the reasonable cost should make JDEM the natural choice for the first Beyond Einstein missions.

Peter Bender, Physicist, JILA and the University of Colorado, 3/18/07 “To the Beyond Einstein Program Assessment Committee” This message is in response to the NRC request for input from the scientific community on the missions planned under the NASA Beyond Einstein Program. It concerns the astrophysical and other information that can be obtained from gravitational wave observations by the Laser Interferometer Space Antenna (LISA) Mission. As you know, joint studies of this mission by ESA and NASA currently are in the Formulation Phase, and a LISA Pathfinder Mission is scheduled for launch in 2009. The Pathfinder mission is being funded by ESA, with NASA contributing a Disturbance Compensation System for flight validation on the mission. The astrophysical information that LISA is designed to obtain concerns primarily the role of massive black holes (MBHs) in the hierarchical growth of galaxies in the early universe, and the processes by which the MBHs initially formed and grew. The term MBH is used here to include black holes with all masses from the intermediate mass range (roughly 100 to 100,000 solar masses) up to the few billion solar mass supermassive black holes seen in quasars at redshifts of up to 6. It is now well known that all or almost all galaxies with high mass spheroids at their centers contain MBHs. In addition, there is a close relationship between the velocity dispersion in the galaxy and the mass of the MBH. When smaller early galaxies merged, their MBHs are expected to have sunk to the center of the new galaxy, and formed close MBH binaries. A number of mechanisms have been suggested by which such close MBH binaries are likely to have merged in less than a Hubble time. The gravitational waves from such mergers out to redshifts of about 10 would give strong signals that LISA can measure in detail. The distribution of such signals with redshift and the masses of the MBHs will provide unique new information that probably cannot be obtained in any other way on the mergers of early galaxies and the whole structure formation process. And accurate measurement of the MBH spins will provide additional information on the MBH growth mechanisms. A second major objective of LISA is to determine how MBHs initially formed and grew. It is not yet known which of four or more scenarios were responsible for the initial formation and growth of most MBHs. All of the known scenarios have possible problems. One is growth from 100 solar mass or larger black holes formed from collapse of massive Population III stars. A second is rapid collisions of very massive stars in the centers of globular clusters, leading to growth beyond about 240 solar mass before supernova collapse to an intermediat mass black hole (IMBH). Third, collisions of 10 to 20 solar mass black holes in galactic nuclei could in principle lead to IMBH formation, if the central densities were high enough. And fourth, massive gas clouds could avoid fragmentation and collapse directly to supermassive stars, followed by rapid evolution to a 100,000 solar mass or larger MBH. It also seems quite possible that a different scenario led to the early formation of the supermassive black holes seen in early quasars than was responsible for the roughly 3 million solar mass and larger black holes seen in many nearby galaxies. The distribution of IMBH and MBH masses seen by LISA in binary mergers will provide valuable information on the formation process for MBHs. Extremely sensitive tests of general relativity also will be obtained by LISA. For such tests, and for verifying that the massive dark objects in galactic nuclei really are MBHs, the LISA mission has unique capabilities. There are expected to be many inspirals per year of roughly 10 solar mass black holes into 100,000 solar mass or larger MBHs in galactic nuclei. During the last year before coalescence, when the lighter mass black hole is traveling at roughly half the speed of light, about 100,000 cycles of the gravitational wave signals can be observed. After fitting the recorded signals with possible initial conditions, masses, and spins for the binaries, if there are persistent deviations of more than roughly a tenth of a cycle from the predictions of general relativity, this will indicate a breakdown of our current understanding of gravitational theory. In addition, the much stronger signals from MBH binaries with both masses large will test the dynamical aspects of the theory, provided that improvements in numerical calculations of the predictions of the theory are accurate enough, which now seems very likely. Thus LISA will provide nearly ideal tests of general relativity. In view of the opportunities for major scientific breakthroughs discussed above, I believe that the science gravitational wave observations in space can provide deserves a high priority in the Beyond Einstein program. Sincerely, Pete Bender

Rachel Osten, Hubble Fellow, University of Maryland, 3/19/07 “5 minute oral remarks” My name is Rachel Osten, and I am a Hubble Fellow at the University of Maryland. I am a multiwavelength astronomer who uses primarily X-ray and radio observations to study nearby stars in order to understand the detailed processes occurring in stellar outer atmospheres. The main thesis I would like to convey to you in my 5 minute talk is that the wider purview of the Constellation-X mission touches all areas of astrophysics, such as stellar coronae. There are many avenues of research which simply cannot be done at other wavelengths. Let me take a few examples from my own field to convey the valuable science opportunities which Constellation-X can address. Magnetic fields are of fundamental importance to producing and controlling the high temperature (``million degree plus'') plasma that exists in the solar corona and the coronae of other stars. X-ray observations provide a probe of this thermal coronal plasma which cannot be done by observations on the ground. Magnetic reconnection produces transient explosive events observable on the Sun and other stars. These flare events have several consequences: In our increasingly technical age, where we rely on spacecraft for telecommunications etc., it is important to understand how our space environment is affected by these impulsive energy releases from the Sun. The NASA program Living With a Star addresses this with detailed studies of the Sun. Yet the Sun is only one star, and observations of stellar coronae across a wide range of stellar parameters are needed to understand what controls the high energy emissions and variations. The brightest stellar coronae which can be studied spectroscopically using the current X-ray instruments are also those which are the least like the solar corona. Detailed coronal studies of nearby solar-like stars are beyond the reach of current observatories due to insufficient collecting area. A second point: X-ray observations of young stars reveal a complex interplay between structures on the star and the disk out of which planets form. Recent results with Chandra have shown that the biggest stellar flares extend far enough from the stellar surface to interact with the disk of gas & dust. The turbulence in the disk induced by stellar flares may be enough to overcome the gas drag tugging on the newly formed planets.These conclusions were based on CCD resolution spectra; studies done at higher spectral resolution and sensitivity may well confirm such results, but surprises may just as readily be hiding. At this point, we don't know. Why do we need Constellation-X? Stars are point sources; you need spectroscopy in order to extract physically meaningful information about their coronae. With prior X-ray missions, only the brightest objects could be studied spectroscopically. This places limits on the regimes which can be studied as well as the conclusions which can be drawn. As an example, Chandra is preparing to spend half a million seconds staring at one young star in order to gain a better picture of how stars, in the process of forming, interact with and are affected by their environment. Yet this is only one star, in one star formation region. While this observation will provide breakthroughs, a sample size of greater than one object is needed to understand fully the extent of environment and stellar parameters at a level which allows comparisons with models. This kind of science can be done with a 15'' angular resolution, and with moderate depth exposures. Observations with Constellation-X will not only be resolving existing questions, such as I've just described; they will also be opening up new fields. We will be able to answer questions which have not yet been posed due to the limitations of the current technology. I've touched on only a few examples of the exciting science Constellation-X can do.

Frederick J. Raab, Head of LIGO Hanford Observatory, 3/28/07 “comments on beyond Einstein” I wish to express strong support for giving the LISA mission a high priority in the selection of space missions. I have no direct role in LISA; my LIGO hat keeps me fully subscribed. But to fully exploit the astrophysics potential of gravitational-wave detection will require regular detections from terrestrial detectors and LISA. LIGO and LISA are entirely complementary in their ability to understand the astrophysics of the gravitational-wave sky just as optical and radio astronomy were necessary to get a handle on the electromagnetic sky. We are hopeful that LIGO will end the "discovery era" of gravitational-wave detection still within this decade. Maybe so, maybe not. But we are confident that LIGO will be regularly detecting gravitational wave sources by the 2015-2020 time scale, thus ushering in the era of gravitational-wave astronomy. Having LISA flying on a comparable time scale would give us the ability to fully exploit this new astronomy from the realm of stellar to galactic sources. This is clearly a superior way to exploit the science. This also is a unique opportunity for cross-agency fertilization between NASA and NSF. Sincerely, Fred Raab

Steven Weinberg, Professor, University of Texas at Austin, 3/29/07 “For the Program Advisory Committee” To the Beyond Einstein Program Assessment Committee: Evidence continues to mount that inflation occurred and that it played a central role in determining many of the properties of the observable Universe, including the relative isotropy of the background radiation, the flatness of space, and the large-scale structure of matter. The physics underlying inflation represents one of the greatest, if not the greatest, challenge to our understanding of nature in general, and in particular to the description of gravitation under conditions of enormous energy density that obtained during the era of inflation. It is highly suggestive that this energy density, as measured from the intensity of temperature anisotropies in the cosmic microwave background, is at just about the level at which the symmetry unifying the different forces of nature is believed to have been broken. The exploration of inflation thus offers a prospect of illuminating the great problem to which Einstein devoted the latter years of his life: the development of a unified theory of gravitation and the other forces of nature. I can think of no grander purpose for a program entitled “Beyond Einstein.” The hope that a NASA mission could move us closer to achieving this dream motivates this letter. Fortunately, the physics of the inflationary epoch has left its imprint upon several observable quantities, including the primordial distribution of matter. I have attended a departmental colloquium given by Professors Eiichiro Komatsu and Daniel Jaffe here at the University of Texas. The subject was a proposed mission, the Cosmic Inflation Probe (CIP), whose Principal Investigator is Dr. Gary Melnick at the CfA. I found myself very impressed with the ability of CIP to further our understanding of inflation through the straightforward yet powerful technique of measuring the galaxy distribution at high redshift (i.e., z ~ 3 - 6.5). It is also my impression that this mission is not only technically feasible, but could readily be flown in the near future. CIP would trace the history of inflation by determining the primordial power spectrum of matter. To do this, CIP would measure the spatial and the redshift distributions of galaxies in the early Universe, when the distribution was still largely primordial. Redshift surveys whose sources lie at lower redshifts, i.e., z < 3, unfortunately suffer from several effects that significantly obscure the desired primordial distribution. Using the shape of the power spectrum of primordial fluctuations to constrain inflation models is a very effective technique. Many studies have historically employed this approach, most notably those using information derived from the cosmic microwave background (CMB) radiation measured by WMAP. CMB measurements have provided exquisite detail about the power spectrum on very large spatial scales, but this technique is unable to provide the much needed data on smaller spatial scales due to foreground contamination. CIP avoids this problem by surveying bright point-like objects over a relatively small area of sky. By doing so, CIP is able to extend the power demonstrated by CMB experiments to physical scales that will provide new information about inflation. Because the tightest constraints are set by measurements that explore the largest range of physical scales, the combination of CIP and CMB data offers the strong potential for identifying the physics that drove inflation. For example, the combination of CIP and PLANCK data will constrain the shape of the power spectrum specifically the first and second derivatives much better than could be done by either mission alone. Thus, it may be possible to determine the nature of the scalar field or fields that drove inflation, including the shape of the potential, and whether a single or multiple fields govern inflation. Measuring the B-mode polarization of the CMB, as proposed by CMBPol, provides another means of studying inflation. An unambiguous detection of the B-mode polarization would be the smoking gun that inflation occurred and I strongly support such measurements as well. Inflation is an indispensable component of the Big Bang model, and we must have better observational constraints if we are to understand the physics that drove the birth of the observable Universe. The two cleanest observables from inflation are the shape of the matter power spectrum and the amplitude of the primordial gravity waves. I understand the major difficulties facing science funding within NASA. However, the surest way to engender continued support from the nation as well as from the physics and astronomy communities, I expect is to focus on questions of broad and fundamental interest. Few questions can compete with “How was the Universe born?” I believe that CIP and CMB polarization missions will play an extremely important role in helping to answer this question and I hope that inflation studies are a very high priority in your deliberations. Sincerely yours, Steven Weinberg

Xavier Siemens, Division of Physics, Mathematics and Astronomy, California Institute of Technology, 3/30/07 “Decision on Beyond Einstein” Dear Colleagues, I am a post-doctoral researcher at Caltech working with LIGO and the Theoretical Astrophysics group. I have worked on cosmic string gravitational wave phenomenology and searches for the past few years. LISA will provide a rare and powerful probe of early universe physics and string theory, and I am writing in support of this experiment. Cosmic strings may form in phase transitions in the early universe due to the rapid cooling that takes place after the big bang. In string theory motivated cosmological models, cosmic strings may also form (in this case they been dubbed cosmic superstrings). Cosmic strings and superstrings generate a background of stochastic gravitational waves, a gravitational analog of the cosmic microwave background, as well as bursts of gravitational waves. The detectability of the bursts and background depends on the properties of the strings that form, e.g. how massive they are, and how readily they interact with one another. LISA will be able to detect both bursts and background in large and relevant areas of the parameter space of cosmic string models--areas that are inaccessible to existing and planned ground based gravitational wave detectors. Due to the frequency range LISA is sensitive to, for much of the parameter space of cosmic string models LISA is orders of magnitude more sensitive than ground based detectors. The gravitational background is generated before the time of recombination. A detection of this background would open an observational window onto a time beyond which the universe is opaque to electromagnetic waves. The detection of a burst would allow us to gravitationally observe an individual cosmic string--in the case of superstrings possibly the fundamental stuff we're made of. As you know these are but a few of the potential scientific breakthroughs that LISA will deliver. Sincerely, Xavi Siemens

Curt J. Cutler, Senior Research Scientist, JPL, 4/2/07 “To The Beyond Einstein Program Assessment Committee” Dear Committee, I’m Curt Cutler, a theorist who works on gravitational-wave sources and data analysis methods. I’m a Senior Research Scientist at JPL, a Senior Faculty Associate at Caltech, and for some years have been a member of the LISA Science Team. My personal belief is that the Beyond Einstein Program contains an especially strong slate of missions, and that it is a great shame that the planned NASA budget will not allow more than one of them to go forward with significant funding in the next few years. I don’t envy your task of deciding on priority among these fine missions. But since the Committee has solicited inputs, I would like to mention some LISA work that I have been closely involved with. Quite a bit of effort has gone into estimating how accurately LISA will determine the physical parameters of the systems it detects. Largely because LISA sources tend to be fairly long-lived (radiating in the LISA band for months to years or more, so that tens to hundreds of thousands of gravitational-wave cycles are observed), and partly because some of the sources will be extremely strong (with matched- filtering signal-to-noise ratios of hundreds to thousands), LISA should be able to determine many of the physical parameters of detected systems to rather remarkable accuracy. For merging massive black hole binaries detected at z=1, it should be possible to determine both masses to ~0.1%, and their spins to ~0.1-1%. This sort of accuracy enables a great deal of interesting science. For instance, the spin values are indicative of how the massive black holes formed and grew. Black holes that grew mainly by gas accretion from a disk would be expected to have high spins, while those that grew mostly by mergers of smaller black holes should have low spins (since then the black hole’s angular momentum grows like a random walk). It also enables precision tests of strong-field general relativity. The physical parameters of the binary can be determined to high accuracy from the inspiral phase alone, and thanks to recent advances in numerical relativity, these parameters will lead to a unique prediction for the waves from merger and ringdown, which can be compared to LISA’s observations. Extreme-mass-ratio inspirals (e.g., inspirals of ten-solar-mass black holes into million-solar-mass black holes) will yield measurements of even more impressive accuracy. It should be possible to determine the two masses and the spin of the massive black hole to ~0.01%. And if one imagines slightly widening the source model, to accommodate a non-Kerr value for the quadrupole moment of the central black hole, then it should be possible to measure that quadupole moment Q to ~0.1%. The measured value can then be compared to the Kerr value, Q = -S^2/M (where S and M are the black hole’s spin and mass), effectively testing the no-hair property of black holes. Of course, the event rate for these inspirals is still quite uncertain, but it is very encouraging that the best current estimates lead to LISA detection rates of ~50/yr. I am also involved in the Mock LISA Data Challenges. This is a community-wide effort to build up data analysis tools for LISA and to test those tools in challenges to analyze blind synthetic data sets. Ten groups took part in the first round of Challenges (which ended in Dec., 2006), developing codes to search for multiple, overlapping (in frequency) white dwarf binaries as well as for massive black hole inspirals. The second round of Challenges (to finish June 15, 2007) is considerably more complicated, requiring the analysis of a two-year-long synthetic data set containing signals from a whole Galaxy of white-dwarf binaries (about 26 million sources, of which several thousand should be individually resolvable), plus several each of massive-black-hole-binary inspiral and extreme-mass-ratio inspiral signals. I believe that the work on these Challenges is testimony both to the strong commitment to LISA in the gravitational-wave community, as well as to the significant, and steadily improving, maturity of the tools and techniques for LISA data analysis. Finally, let me say that while a great deal of wonderful science will come from the better-understood LISA sources, some of which is briefly discussed above, in my opinion at least half the excitement of LISA comes from opening the window on the low-frequency gravitational-wave band, to see what surprises are there. Several mechanisms for generating a detectable stochastic gravitational-wave background have been analyzed in the literature, e.g., cosmic (super)strings or a strongly first- order phase transition at the TeV scale. While perhaps none of these scenarios has a high probability of occurring, they all have illustrative value: there are many plausible ways that a detectable background could have been produced. And any such detection would almost surely have profound implications for fundamental physics. Thank you for your attention. Sincerely, Curt J. Cutler Disclaimer: The opinions expressed above are my own, and do not necessarily represent the policy or opinion of JPL.

Steinn Sigurdsson, Associate Professor, Pennsylvania State University, 04/04/07 “Short Comment on Beyond Einstein” Dear Colleagues, I'm writing this comment to summarise and elaborate upon my brief oral comment to the committee at the Chicago town hall meeting on April 4th 2007. A significant part of my current research interests are relevant to astrophysical LISA sources, including: extreme mass-ratio inspirals of low mass compact objects; assembly of supermassive black holes in cosmological context; and, binary supermassive blackholes. I have encouraged my recent postdocs and students to get directly involved in LISA related research, motivated by the prospects for observations in the finite future. Several of them have moved to do so, excited by the scientific prospects. All the proposed Beyond Einstein missions are of the highest quality and ought to be supported, and several of them are relevant to my research interests, but I would like to make some case for LISA. LISA will open new scientific fields; it opens three decades in frequency, in a band completely inaccessible from the ground, opening a vista to otherwise inaccessible physical processes. LISA offers prospects for tests of fundamental physics, including gravity in the strong field regime. LISA also has guaranteed astrophysical calibration sources, and provides the prospects for serendipitous new discoveries. Extreme mass-ratio inspirals are a promising class of astrophysical sources. Compact obects with masses ranging from half a solar mass or so for most white dwarfs, up to tens or hundreds of solar masses for stellar and intermediate black holes, will spiral into supermassive black holes with masses of a million or so solar masses. These events are certain to happen in the dense stellar environment in the centre of normal galaxies, and very likely to happen at rates high enough to provide multiple LISA detections, they provide near test-body probes of the strong field of the black holes (and probe the mass and spin of the black hole, and for the brighter sources test the relativistic nature of the field, including the presence of any additional "hairs" due to scalar fields or additional hidden gauge fields). In addition to the steady flow of compact objects in normal galaxies in the local universe, in current models of structure formation we expect a lot of intermediate mass black holes to form from the first stars, at redshifts greater than 10. These form in low mass dark matter halos which collapse early and then merge, typically into the nearest high mass halo. There the black holes are expected to merge in significant numbers with the central black hole of the dominant halo; this process provides a high, albeit speculative, source rate for LISA, probing structure formation at redshifts > 6. This tests the assembly history of the supermassive black holes, and indirectly the parent dark matter halos; probes the early accretion history of these black holes, and the origin and fate of the first stars. Recent models consistently predict interesting rates of such mergers, but different assumptions lead to rates and mass profiles that differ by factors of several at different redshifts; LISA can test these models and explore the theories of the earliest structure formation and, indirectly, the physics of the cold dark matter that dominates the assembly of this structure. Count rates of sources with luminosity distances measured to ~ 20-30%, and enough counts to have poisson errors of ~< 30% in each distance interval (ie tens of detected sources over a range of distances) would suffice to discriminate current models. Higher precision enables stronger tests of the physics of the objects as well as the astrophysical source processes. This is only one of several interesting physical processes we know can be explored with LISA, and make the prospects of observations of low frequency gravitational radiation very interesting. LISA science is highly complimentary to other planned projects, including deep synoptic sky surveys, high redshift radio observations, deep space based infrared observing, and sensitive high energy observations. The prospects for finding electromagnetic counterparts to gravitational radiation sources is particularly exciting and offers additional leverage for LISA science, and more relevance to additional scientific questions. LISA promises exciting new science that can only be done from space that tests theories and addresses fundamental astrophysical questions with interesting precision. Yours sincerely Steinn

Anne Ealet, CNRS, 04/05/07 “5 minute statement made on April 4 2007 at the Beyond Einstein Program Town Hall Meeting, Chicago” To the Beyond Einstein Program Assement Committee My name is Anne Ealet. I am a French particle physicist in Marseille, working now in cosmology. I am a member of the SNAP collaboration and I lead the French effort to propose an onboard spectrograph for the mission. I believe that the nature of dark energy is one of the most challenging question of this century. It will certainly open a new fascinating window in the universe and can lead to a revolution on our understanding of fundamental physics and general relativity. The French community is strongly interested in challenging the dark energy puzzle. Some French physicists were involved in the first discovery of the accelerated expansion using SN in the SCP group. The first gravitational arcs where co-discovered by an other French group.It is thus not a surprise that France and Canada have developed the CFHT legacy survey. The first part of this survey is repeatedly imaging in 5 bands 4 square degree searching for Supernovae, and has currently collected a sample of 300 supernovae. The second part of this survey is covering a 170 square degree to measure weak lensing. In parallel to this imaging effort, massive spectroscopy of faint distant galaxies has been possible by building the VIMOS instrument at VLT. With this redshift machine, the VVDS project has measured more than 30 000 spectra enabling to calibrate the photometric redshift technique out to redshift 1.5 Because the French community wants to ensure its involvement in future dark energy projects, we are investigating different approaches such as BAO with radio telescope and WL and SN from space. Some of us in France are involved in the SNAP project since the beginning and we are convinced that the SNAP concept is the best one for some reasons that I will explain now. In order to tackle the dark energy question we need to distinguish any deviation of the general relativity or of the concordance model. This leads to two strong constraints: • Firstly, the mission should provide very precise measurements => controlled at some percent level: for the instrument, it means a dedicated optimisation with very accurate control, implying redundancy and importantly dedicated onboard calibration. • Secondly, the mission should have more than one probe: The most promising dynamical probe today is the weak lensing and the most obvious geometrical probe is supernovae. Thus, I strongly believe that SNAP combining SuperNovae and Weak Lensing with a global optimisation of this two probes is the best instrumental concept to probe dark energy. Although SNAP is a dedicated mission to probe dark energy with high accuracy, it will also address many other important science topics. Among other things, with its nine filters covering the visible and near-infrared, and its visible/infrared integral field spectrograph, SNAP: § will able to determine the photometric redshift of billions of galaxies, necessary to understand galaxy formation and evolution § will construct the 3D map of the dark matter in the Universe, enabling a direct measurement of the growth of structures § will weight the mass of more that 10 000 group and cluster of galaxies, and find more than 10 000 strong lensing systems, which are also potential cosmological probes A key ingredient of the SNAP mission is the dedicated onboard calibration, which is essential to reduce any kind of systematic effects. In particular the SNAP spectrograph covering both the visible and near-infrared will provide important calibration for both the Supernovae and the weak lensing measurementt: § the spectrograph will provide photometric calibration of the mission § the spectrograph will identify and will control the evolution of all supernovae used in the Hubble diagram § the spectrograph will measure the redshift of 100 000 galaxies which are essential to calibrate the photometric redshifts, used in the weak lensing measurements My group is in charge of this spectrograph, and we have developed a novel concept based on image slicers an area where we have a unique expertise. The spectrograph is an important component on SNAP since a long time, and it has been strongly supported by CNES the French spatial agency and by a significant staff in CNRS laboratories. During the last 2 years, we have constructed a full spectrograph prototype with the SNAP specifications that will be under thermal vacuum testing next June, and we will do more prototyping in the next two years. Since our involvement in SNAP, the French spatial agency has identified the dark energy question has one of its priority and has been very active on this topic. In particular, in 2006, a phase 0 study has been conducted on DUNE, which was a concept of a small, low cost telescope optimised for weak lensing measurements. CNES is strongly interested to study a possible higher level partnership with SNAP and has started to conduct a telescope study during 2007 together with two French industrials. In summary I believe SNAP is a very simple telescope although very powerful. Because of the intensive R&D achieved in the last 5 years it is now a very low risk mission. By coming here, my group and I want to support the choice of JDEM for answering the dark energy question.

William Wester, Scientist, Fermilab, 04/09/07 “Written Comments from Chicago BEPAC Town Hall” I am a trained experimental particle physicist and have been working on accelerator based experiments throughout my professional career. I have been fortunate to be involved both in the fundamental science goals and in cutting edge detector development. Attracted by the astronomical evidence for dark matter and the profound discovery of a dark energy in the universe, I became one of the original team members at Fermilab to join the SNAP collaboration. I would encourage the Beyond Einstein Program Assessment Committee to provide support for the timely implementation of the JDEM mission. I. The Coming Revolutions in Fundamental Science Dark Matter and Dark Energy are two mysterious phenomena that require scientific investigation and their understanding will revolutionize our understanding of modern physics. We know these phenomena exist but have limited knowledge in measurements of their properties. We are unable with our current measurements to understand the origin of these phenomena. This is the most exciting time to be an experimental physicist in this field because it will be the forthcoming experimental measurements that will drive the theoretical understanding. In particle physics, while uncovering sometimes subtle effects in the Standard Model has been scientifically enlightening, it is the quest for the next breakthrough discovery that drives the field forward. Similarly, it will be a breakthrough when we uncover enough detail into dark matter and dark energy to give our next insight into the nature of matter and energy. II. Understanding Dark Energy We do not have much of an understanding of Dark Energy and making the next round of measurements with the JDEM mission is the logical next major step. The Dark Energy Task Force parameterized the merit of future initiatives in terms of the error ellipse in the dark energy equation of state parameter and the evolution of that parameter with redshift. A space based mission like JDEM scores very well in the figure of merit in an absolute sense (high figure of merit) and in the sense that the uncertainty in JDEMs figure of merit is small compared with ground based initiatives. Is the equation of state parameter exactly equal to negative one? If so, a candidate explanation for Dark Energy would be Einstein's own rejected cosmological constant. If not, we've learned something fundamental about the nature of dark energy. Similarly, is the evolution of the equation of state parameter with respect to redshift exactly zero? JDEM has well defined science goals that are aimed at addressing these first fundamental questions towards revealing the nature of Dark Energy. III. Understanding Dark Matter We do not have much of an understanding of dark matter and astronomical measurements are currently our best handle towards understanding this mysterious phenomena. Ideally, we'll produce and detect dark matter in particle accelerator experiments or observe a signal in a sensitive ground based experiment as well as continuing to make dark matter astronomical observations and measurements. While the JDEM mission emphasizes its laser sharp focus on the dark energy measurement in its science definition, JDEM will provide a unique and immensely rich data sample from which one can observe the effects of dark matter and perhaps allow for the extraction of its properties. IV. Understanding the Unknown We do not know what there is yet to know. A final point is to emphasize the unique rich data set that a JDEM mission would provide in terms of its ability to encounter new observations with large statistics in a way that might uncover the next great mystery of our understanding of matter and energy. It is hard to quantify this opportunity but a wide area, deep survey over a large wavelength range feed into this opportunity. JDEM is positioned to provide such a rich data sample. In conclusion, I described the primary science opportunity of the JDEM mission to measure dark energy parameters which requires a space-based mission to be most certain of obtaining small uncertainties on those parameters. In particular, I tried to address the BEPAC question regarding the long-term goals for science beyond the science goals of the mission. I highlighted the mysterious known phenomenon of dark matter and alluded to the fact that there may be other breakthrough discoveries for phenomena that are yet unknown. By providing a wide area, deep survey over multiple wavelengths the JDEM mission should give a fantastic opportunity for such breakthrough discoveries.

Michael S. Turner, Bruce V. & Diana M. Rauner Distinguished Service Professor, Depts. of Astronomy & Astrophysics and Physics, Enrico Fermi Institute, University of Chicago, 04/09/07 1. Progress and discoveries since publication of Q2C have made Q2C science and recommendations even more timely and compelling. The paragraph below was a quick summary I prepared for the Interagency Working Group: In the 5 years since Quarks to the Cosmos was released there have been exciting developments at the boundary of astronomy and physics. They are indicative of the continuing rapid pace of progress in this exciting area of discovery science and add to the case that the fields of particle physics and cosmology are poised for major advances in our understanding of the Universe and the laws that govern it. Three laboratory-based experiments involving significant U.S. participation have now confirmed the astrophysical evidence for neutrino mass and have narrowed the mass range (MINOS at Fermilab; KamLand and K2K in Japan). NASA’s WMAP satellite successfully mapped the CMB sky with unprecedented precision and resolution. WMAP’s results together with the large-scale structure measurements of the SDSS survey have determined cosmological parameters to percent-like precision (e.g., age of 13.7 Gyr and spatial flatness both measured to 1%); provided the first strong evidence that the Universe underwent a burst of rapid expansion (cosmic inflation) shortly after the big bang and have given a complete census of energy and matter in the Universe (4% atoms, 23% dark matter and 71% dark energy). The SDSS/WMAP determination of the basic parameters and large-scale features of the Universe was named Science Magazine’s Breakthrough Discovery for 2003. Additional evidence for the mysterious dark energy that is causing the expansion to speed up came from the SDSS and WMAP results, additional supernovae measurements, both from the ground and the Hubble Space Telescope, and x-ray measurements of clusters by the Chandra x-ray Observatory. The discovery of a new signature of cosmic acceleration (baryon acoustic oscillations) in the large-scale distribution of galaxies (by the SDSS) has opened the window to a new method of probing dark energy. The additional data have not only made the case for cosmic acceleration air tight, but have also begun to probe the nature of the mysterious dark energy causing the speed up. Evidence that the bulk of the dark matter is not made of atoms continues to mount (e.g., the violent collision of two galaxy clusters where the collision has separated the atomic matter and dark matter and the WMAP/SDSS census of material in the Universe) and the NSF/DOE supported CDMSII dark-matter search reached the highest sensitivity of any experiment to date in its direct search for the dark matter particles that compose the halo of our galaxy. CDMSII has begun to test the predictions of supersymmetry for the dark matter particle. The two LIGO gravitational-wave detectors have achieved and even exceeded their design sensitivity and began a year-long search for gravitational waves from neutron-neutron coalescences, black hole collisions and supernovae, putting us on the verge of discovering gravitational waves and confirming the last major prediction of general relativity. Heavy-ion collisions at the RHIC facility at BNL revealed evidence for an unexpected new state of nuclear matter, something akin to a superfluid. The BaBar experiment at SLAC discovered evidence for CP violation in the B-meson system, providing new evidence for the slight difference in the laws of physics for matter and antimatter (which is crucial to the Universe ultimately evolving more matter than antimatter and avoid the annihilation catastrophe that would leave it devoid of matter). BaBar also precisely probed the consistency of the standard model of particle physics – no cracks yet. RunII at Fermilab’s Tevatron which is still in progress, has produced important results, including the discovery of a new form of matter/antimatter oscillations (involving the B_s meson and which could also shed light on the origin of the matter/antimatter asymmetry in the Universe) and a very accurate determination of the mass of the carrier of the weak force (the W boson) which adds further evidence that the Higgs boson exists, is light and may be discovered soon. The Pierre Auger Observatory is nearly complete, is operating and has already accumulated the largest and highest quality dataset of Nature’s highest energy cosmic ray particles. Auger scientists should soon be shedding light of the origins and nature of the ultra-high energy cosmic rays. The 10-meter South Pole Telescope, designed to study dark energy and search for the signature of inflation in the polarization of the CMB was successfully deployed at the South Pole and has begun taking data. Two experiments using reactor neutrinos to search for oscillations between electron and tau neutrinos and involving U.S. scientists supported by DOE and NSF, Chooz and Daya Bay, are now under construction (?). The parameter they seek to measure, called theta_13, is critical to designing the next generation of neutrino experiments to study CP violation among neutrino with the ultimate aim of understanding how the asymmetry between matter and antimatter in the Universe evolved. In 2008, the LHC will begin science operations, with the Higgs boson, supersymmetry and the dark matter particle being discovery prime targets. In the same year, the Planck Survey satellite, a joint ESA/NASA mission to study the CMB with better resolution and polarization sensitivity than WMAP, will be launched. The first construction funds for Advanced LIGO, the upgrade which will improve its coverage of the Universe a factor of 1000 and all but insure the detection of sources, are n the President’s 2008 budget for NSF. A group of DOE and NSF supported astronomers and high-energy physicists have submitted a full construction proposal for the LSST to the NSF. While much remains to be done to realize the full discovery opportunities at the interface of particle physics and cosmology, the past five years have both seen important progress and additional discoveries which continue to indicate that we are on the verge of a revolution in our understanding of the fundamental features of the Universe as well as that of matter, energy, space and time. In addition, there seems to be another lesson: progress to date has been due both to investments at the interface important and at the core of both particle physics and astronomy. Research at the interface of two fields cannot flourish unless the two fields themselves are healthy. 2. The NASA’s Beyond Einstein program is a coherent set of missions that address well the Q2C science. To achieve the full set of stunning opportunities at the interface of astronomy and physics, all of the Beyond Einstein missions must be implemented. This point has been emphasized by many scientists who have presented to BEPAC. (While I only attended one town meeting (in Chicago), I was deeply impressed by the passion and energy of the scientists working on BE science – this speaks volumes to the vibrancy of the area and the compelling nature of the science.) 3. The mystery of cosmic acceleration and dark energy just may be the most profound problem in all of science today (and perhaps even of our time). Just think, while the defining feature of gravity is its attractiveness, in the largest arena – the Universe – it is repulsive! While there is no compelling model with a set of predictions that can be tested, it is possible to test and even rule out the minimal hypothesis: namely that cosmic acceleration is simply due to a cosmological constant (quantum vacuum energy) within the theory of general relativity. That hypothesis can by ruled out by showing one (or more) of the following: 1. w is not equal to -1; 2. w varies with time; 3. dark energy clusters; and 4. cosmic acceleration is not self consistently described by general relativity. If a cosmological constant is ruled out, that means the explanation is even more revolutionary – some new form of energy or a modification of general relativity. Not surprisingly, dark energy has captured the attention of a great number of astronomers and physicists, and while a large number of experiments are beginning to probe w, their ultimate precision and reliability are limited by systematics which cannot be reduced or controlled without the two large-scale projects endorsed by Q2C (JDEM and LSST). In particular, in 2002 a space-based experiment seemed essential if the systematics are to be controlled, and that case is at least as compelling today. The reasons are very simple: only space offers the ability to do the wide-field, diffraction-limited observing (needed for SNe, Weak Lensing and BAO) and only space allows one to observe in the infrared (where most of the energy from high-redshift objects arrives). The Q2C realized the very significant potential of LSST to probe dark energy, but also appreciated that the significant improvements in the control of image quality (more than an order of magnitude) were required to achieve them. The combination of LSST and JDEM offered very significant improvement in controlling systematics and probing dark energy at relatively low risk (JDEM) and the opportunity for even more probative power (but at significant risk) and complementary results that when combined with JDEM would probe dark energy even more decisively. 4. I am sure that partnering issues have not escaped BEPAC’s notice. LISA and JDEM rely on significant contributions (both financial and technical) from partners (ESA in the case of LISA and DOE in the case of JDEM). I believe that the staging of the BE projects should take into consideration the schedules and desires of the partners.

Sean McWilliams, Graduate Research Assistant, University of Maryland, 04/11/07 “5 minute oral statement at the Beyond Einstein Program Town Hall Meeting, Baltimore, MD, March 14, 2007” Good afternoon, ladies and gentlemen. My name is Sean McWilliams. I'm a graduate student in the physics department at the University of Maryland, and my research focus is numerical relativity and its application to gravitational wave data analysis. As you may know, the field of numerical relativity has entered a period of rapid progress in the last few years. Several groups now have stable numerical codes which are capable of evolving two comparable mass black holes from the late inspiral through the merger and into the ringdown for nearly any parameter set of interest. We therefore have a very concrete prediction from full non-linear general relativity for the gravitational radiation emitted during the final merger of two black holes. Now all we need is a measurement to compare with our predictions. The ground-based gravitational wave detector LIGO can only achieve signal-to-noise ratios of roughly 10 at best for stellar mass binary black hole mergers. Advanced LIGO, which is LIGO's planned upgrade, may achieve SNRs of 100, but only for intermediate mass mergers, and there is no observational evidence for the existence of intermediate mass black holes. LISA, on the other hand, would observe the mergers of supermassive black hole binaries with SNRs as high as 10000 out to z of 1, and on the order of hundreds as far back as galaxies have existed. The observational evidence for the existence of supermassive black holes at the centers of galaxies is substantial, and the model of hierarchical structure formation predicts the merger of these core black holes when their host galaxies collide, which would lead to a relatively substantial event rate of tens to hundreds of mergers per year. Therefore, while LIGO can only hope for a detection, and Advanced LIGO may be able to measure parameters from mergers with modest accuracy, but with a highly uncertain event rate, LISA will be able to perform precision measurements of gravity in the strong field regime. These measurements will provide the most conclusive test of general relativity possible under the most extreme conditions nature can provide. As a graduate student, I chose to pursue my current research path because I view the field of gravitational wave astronomy which LISA could facilitate as the most promising frontier for discovery in physics in the 21st century. One obvious difference between LISA and the other Beyond Einstein missions and, in fact, every other mission that has ever flown, is that it isn't making an electromagnetic measurement. LISA is opening a new window on the Universe, like radio astronomy did a half a century ago. We have certain expectations of what we will see with LISA based on what we have seen in the past electromagnetically, but the fact of the matter is that our current prediction of what the gravitational wave sky will look like may bear little resemblance to the genuine article. There may be electromagnetically dark-yet-gravitationally powerful sources that were unexpected. We may discover unexpected gravitational phenomena behind poorly understood electromagnetic observations such as short gamma ray bursts. And because gravitational observables fall off as 1/r instead of 1/r2, we will have information about the gravitational wave sky at distances where we have no electromagnetic information to inform our predictions. Every time we have explored new areas of the EM spectrum, we have discovered something new and profoundly unexpected. Now we have the prospect of not simply exploring new wavelengths, but a completely new medium. The possibilities for discovery seem endless and, as of yet, completely untapped. Thank you all for your time.

Adrian Melissinos, Professor of Physics, University of Rochester, 04/12/07 “Input to BEPAC” Dear BEPAC committee, There is no doubt that all three missions hold great scientific promise and address critical problems in our understanding of Nature and of the Cosmos. These are defining problems for the science of the 21st century. I do however find LISA most compelling because in addition to the wealth of astrophysical observations that it will make using gravitational wave signals from mergers and collapse of binary systems it can also address one of the central issues in experimental cosmology: the detection of a stochastic gravitational background. It is often overlooked that LISA can detect a stochastic signal without having to resort to a cross-correlation measurement. I estimate the sensitivity of LISA at ~2x10^(-3) Hz to be h=10^(-23)/sqrt(Hz) for SNR=5. This translates to a limit on the normalized gravitational energy density (per log frequency) of Omega = 10^(-16). This limit is below even the standard inflation model prediction of 10^(-15). At these low frequencies one will have to separate the cosmological contributions from the astrophysical stochastic background but this should be feasible. Sincerely, Adrian Melissinos

Vicky Kalogera, Associate Professor, Northwestern University, 04/19/07 “Notes from Open Mic address at the Chicago Town Hall Meeting (April 4, 2007).” Dear Colleagues, My name is Vicky Kalogera and I am an associate professor of physics and astronomy at Northwestern University. My research work is primarily focused on close binaries with one or two compact objects, and specifically on their origin and evolutionary history. I study such systems in different forms: as binary pulsars, X-ray binaries, gravitational wave sources, and possibly gamma-ray bursters. I try to understand them as both individual objects and as whole populations and I examine them often in the context of their interaction with their stellar environments with different star formation or stellar dynamical histories. When I look at the range of science opportunities in the Beyond Einstein Program, I anticipate with most excitement those offered by the LISA and Con-X missions. Let me elaborate on some of the main reasons for this, having in mind the questions you asked us to consider. As you already know, Con-X’s most exciting promise is the combination of high-resolution X-ray spectroscopy with high sensitivity. Such studies will allow us to probe one of the two fundamental properties of black holes: their spins, dynamical measurements of which have not been possible so far. It is well understood that this is science that cannot be achieved with any of the current X-ray observatories effectively because of the prohibitively long exposures needed (several hundreds of ks per source for Chandra, whereas Con-X promises science pay-offs with just a few ks) - with 100’s of ks on Con-X we would be able to measure the spins of not just a handful of interesting black holes, but instead probe a whole population and create big enough samples to do reliable astronomy and astrophysics. On the question of long-term goals for science and the opening of new fields, I find that the LISA mission holds the strongest and most exciting promise. The idea that in about a decade we could be learning about compact objects through not just electromagnetic radiation, but also gravitational waves is a major motivation for pursuing compact object studies. We expect that opening this fundamentally new observational window will advance our knowledge in physics and astronomy in at least three different ways: (i) enable large-scale astrophysical studies of phenomena/systems we already observe electromagnetically but with limited detection efficiency: e.g., population characteristics of Galactic white dwarf binaries throughout the Milky Way; demographics of supermassive black holes out to large redshifts in mass regimes that are difficult to probe from the ground; (ii) reveal new physics related to cosmic sources we already know exist: e.g., mapping the spacetime around supermassive black holes in centers of galaxies, dynamically and precisely measuring their masses and spins, and at the same time probing the complex stellar interactions in dense galactic center regions; (iii) reveal new sources theorists have predicted, but are not firmly known and widely accepted to exist through some other type of observations: e.g., intermediate-mass black holes with formation histories distinct from stellar-mass and supermassive black holes, and actual mergers of supermassive black holes. Apart from the opportunities for fundamental physics with tests of strong-field gravity, the prospect for gravitational waves becoming routine probes of the cosmos and astrophysics is most exciting to me as an astrophysicist. Having LISA source detections that allow us to predict the timing of black hole mergers and facilitate electromagnetic observations of such events could prove to be a pivotal factor in the astrophysical studies of such mergers and their effect on their galactic environments. It is important to note that progress in astrophysics relies critically on the close interaction between observations and theory. It is through such comparisons and resultant derivations of constraints that our physical understanding improves and paradigms get shifted. For the science targeted by the LISA and Con-X missions, the theoretical framework is indeed mature and ready to be tested and further developed by unique observations provided in the coming decade.

David Reitze, Professor of Physics, University of Florida, 04/26/07 “Comments to BEPAC in Support of LISA” Dear Colleagues, I write to you today on behalf of the LIGO Scientific Collaboration to express our strongest support for the LISA mission. I am a Professor of Physics at the University of Florida and currently serve as the Spokesperson for the LSC, a group of approximately 500 researchers dedicated to carry out the scientific program of the LIGO and GEO600 gravitational wave detectors. The LIGO Scientific Collaboration seeks to detect gravitational waves, use them to explore the fundamental physics of gravity, and most importantly to develop gravitational wave observations as a tool of astronomical discovery. We are currently near the end of our first long search, and a major upgrade of the LIGO detector is planned in 2011. LIGO is sensitive to a select class of gravitational wave emitters out to a limited horizon, including binary neutron stars and stellar mass black holes, asymmetric supernovae core collapses, and axisymmetrically deviating neutron stars. While we will learn much about the astrophysics of these sources with LIGO, LISA opens up a completely new wavelength region in the gravitational wave spectrum, a band containing very different sources. While LIGO will observe nearby stellar-mass compact objects, often in catastrophic events like supernova explosions in our Galaxy and the nearest gamma-ray bursts, LISA will have the sensitivity and spectral range to study much more massive and distant systems. LISA's observations will complement those of LIGO in the same way as X-ray observations complement optical astronomy. The examples of progress achieved because of pivotal multi-wavelength electromagnetic observations are numerous in the history of astronomy and astrophysics. Gamma-ray bursts stands out in recent years as a prime example, the nature of which were essentially uncovered through afterglow observations in the X-rays, optical, and radio frequencies. In addition, dynamical mass measurements and identification of stellar-mass black holes is completely due to the synergy of optical and X-ray observations. LISA promises to answer many puzzling questions raised by current electromagnetic observations. X-ray observations of ultra-luminous sources and dynamical interpretations of optical observations of globular cluster cores have provided tantalizing, albeit only tentative, evidence for the existence of intermediate-mass black holes. LISA may provide the only direct mass measurements of such black holes, set to rest the question of their existence, fuel our understanding of how they form and evolve in different environments, and show us how they may seed supermassive black hole growth. In addition, LISA promises to provide the only direct evidence that black holes indeed coalesce in centers of galaxy mergers (hypothesized by cosmological simulations and supported by electromagnetic observational evidence). It would possibly allow the discovery of electromagnetic counterparts, which would reveal an immense amount of astrophysical information about these mergers. LISA's anticipated detections of extreme mass ratio inspirals would map not just the space-time around supermassive black holes, but through its rate measurements and mass measurements of the stellar-mass objects would reveal information about the properties of the stellar populations in galactic centers, something that is very hard to probe electromagnetically. Finally, LISA observations will undoubtedly prove to be a goldmine of astrophysical information for the numerous double white dwarfs that must exist in our Galaxy and are extremely hard to discover electromagnetically. Their population provides what is considered guaranteed sources for LISA, and mapping their properties could profoundly change our currently very limited understanding of how close compact object binaries form. The LIGO Scientific Collaboration embraces a membership of a large number of scientists who are dedicated to the development of gravitational wave astronomy, contributing leading-edge skills in technology, source studies, and data analysis. There is a strong overlap with membership of the LISA community in all of these areas, and LISA has benefited greatly from ground-based experience with optical design, data analysis, and theory. However, the LISA community also maintains a strong and enthusiastic following among astronomers. The refereed literature already contains hundreds of astronomy papers inspired by the prospect of LISA, papers that investigate problems that will assist LISA observations or that will benefit from LISA's data. The attendance figures at the bi-annual LISA Symposium similarly show an interest in and enthusiasm for LISA among astronomers that the ground-based detectors have not yet achieved. LISA's high sensitivity and rich variety of sources is truly exciting to all of us. Sincerely, David Reitze For the LIGO Scientific Collaboration

May 10, 2007 To: BEPAC Committee From: WMAP Science Team Subject: The future impact of WMAP on the Inflation Probe mission 1. Purpose of this White Paper The Beyond Einstein Inflation Probe, also known as CMBPol, is aimed at testing models of the birth of the universe by measuring primordial gravitational radiation. This radiation is best detected through its characteristic signature on the polarization of the cosmic microwave background (CMB), the so-called “B-modes.” The Wilkinson Microwave Anisotropy Probe (WMAP) is, thus far, the only instrument to measure the polarization of the CMB at large angular scales. Three years of WMAP data gave us the first glimpse of the astrophysical landscape in which the measurement must be made, and has given us the best limits yet on primordial gravitational radiation. In this white paper, we contend that the best preparation for the Inflation Probe is through continued operations of WMAP. We also contend that the best way to optimize Planck's pursuit of the B-mode signal is through the continued operation of WMAP. 2. WMAP Operations The WMAP satellite is healthy and operating even better than when it was launched in 2001 because it is now very stable. Barring any unexpected malfunctions, the mission has the fuel to operate for many more years. The mission will have collected 6 years of cosmological data by September 2007. Every two years NASA holds a Senior Review to review the smaller operating astrophysics missions (HST, Spitzer, Chandra, etc. are not included in this review), which are funded out of the Mission Operations and Data Analysis (MO&DA) budget. Last year, the Senior Review recommended WMAP observations through September 2008. The tentative baseline plan is to terminate observations in September 2009, but this extra year would need to be recommended by the next Senior Review panel. The WMAP Team expects to have an opportunity to submit a proposal for continued WMAP operations to the next Senior Review panel in Spring 2008. There is no guarantee that such a proposal will be successful, especially as MO&DA budgets are very tight and the Beyond Einstein community is only one of many. 3. Relevance to the Inflation Probe (CMBPol) and the BEPAC The BEPAC is charged, in part, with reporting on what steps should be taken to enhance future Beyond Einstein mission readiness. This white paper is relevant to the BEPAC in this regard, as we continue to learn enormous amounts from WMAP that directly affect the Inflation Probe mission. The lessons fall into three categories: (A) Ever-tightening constraints on inflationary models. Current limits on inflation models are shown in Figure 1, below. Note that some particular inflation models are a better fit to WMAP data than others. Figure 1: Three years of WMAP data (combined with data from the Sloan Digital Sky Survey, SDSS) are used to constrain acceptable values of the inflation parameters, ns (the scalar spectral index of spatial fluctuations) and r (the tensor-to-scalar ratio). Note that the classic pre-inflationary Harrison-Zeldovich values of ns = 1 and r = 0 are disfavored. Also note that inflation is preferred over inflation. Additional data will tighten the observational constraints on inflation parameters. In principle, WMAP can detect large angular scale gravitational waves through two routes. The first is a direct detection of the B-mode signal.  The second is by measuring the shape of the temperature spectrum over a large range of angular scales by combining WMAP data with well-calibrated data from small-scale experiments.  As shown in Fig. 1, the simplest inflation models predict that if ns ~ 0.96, then r ~ 0.2. Based on the properties of existing WMAP data, we estimate that an r ~ 0.2 B-mode signal could be measured at 4s significance with 12 years (total) of WMAP observations.   This would be achieved in about the same time scale as when Planck polarization results become available, and before the Inflation Probe.  WMAP may be better suited than Planck to measure the large angular scale polarization because the WMAP scan strategy produces a wider range of polarization azimuth angles than does the Planck strategy. In addition, WMAP has wider frequency coverage than the Planck Low Frequency Instrument (LFI), and data from extended WMAP operations are likely to be more sensitive than (and at a minimum complementary to) the LFI data if Planck operates nominally. This is especially true for low-l polarization for which the Planck design is not well-suited. WMAP data will also complement data from the Planck High Frequency Instrument (HFI). If Planck suffers from any unexpected launch or performance problems that preclude it from achieving its performance goals, the WMAP large-scale polarization results will be the best available until the Inflation Probe mission flies.  On the other hand, if Planck is successful, the WMAP and Planck results can be inter-compared for consistency, and combined to take of advantage of their complementary wavelength coverage and independent noise properties. When combined, the constraints on inflation will improve beyond the limits of either experiment in isolation. The second detection route requires combining WMAP data with small angular scale measurements to identify the contribution of gravitational waves to the temperature anisotropy. This is how WMAP, when combined with SDSS, currently limits the tensor-to-scalar ratio to r < 0.3 (95% CL).  This limit will improve when SDSS data are replaced in favor of small scale CMB measurements [from the Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT), and other efforts].  Based on a Fisher matrix analysis, the best limit that can be achieved is r < 0.1 (95% CL).  Medium-scale WMAP data are crucial to this improvement, as they provide the calibration for the small-scale CMB experiments. The WMAP data is still noise dominated on these scales. Additional WMAP operations will also improve the low-l EE polarization measurement and will indirectly improve the inflationary parameter fits.  The current data provide a 3s detection of the optical depth, t.  With 12 years of WMAP data and with the use of all of its frequency channels, the significance of this detection can improve by a factor of 6.  This will reduce the uncertainty in the inflationary spectral index, ns. A gravitational wave detection by WMAP and/or Planck would make the case for the Inflation Probe very compelling because it would "guarantee" a high fidelity detection and it would open the possibility of measuring the tensor slope, nt, which would provide an even more stringent consistency test of inflationary predictions. (B) Improved signal-to-noise on large angular scale polarized foreground emission. The Inflation Probe will be a foreground-limited mission. WMAP has shown that the polarized foreground signal will be significant and that when averaged over ~75% of the sky, the foreground minimum will be near 65 GHz. However, more integration time is needed to better characterize the complexity of the foreground emission, which is an important design consideration for the Inflation Probe mission. Below 65 GHz, the dominant polarized foreground signal is due to synchrotron radiation which has a frequency spectrum of n-3.1. The lowest WMAP frequency band is 22 GHz, while the lowest Planck mission band is 33 GHz, thus the synchrotron signal is roughly 3.5 times brighter in the WMAP data than it is in the Planck data. Taking into account the relative sensitivities, the WMAP data will have at least ~3 times the signal-to-noise of the Planck data for synchrotron foreground removal. While the Planck 353 GHz data will characterize the polarized dust emission, the best synchrotron data will be from the WMAP 22 GHz map. If the Planck HFI achieves its science goals, then its polarization measurements will be foreground limited. The factor of ~3 improvement in WMAP’s synchrotron noise could produce a factor ~9 improvement in Planck’s final measurement of r from large scale polarization. Continued WMAP operations will also clarify the degree to which the synchrotron spectral index varies across the sky, and will help to determine if spinning dust contributes to emission in the WMAP frequency bands, in both intensity and polarization. Note that lower-frequency ground-based measurements of the Galactic synchrotron emission are not useful for polarized foreground removal as they are strongly affected by Faraday rotation. (C) Observing and data processing techniques and calibration. Groups around the world are studying the WMAP data to see what they have to account for in their measurements. The WMAP data provide a test-bed for new data processing ideas, and the WMAP team itself learns from its experience and improves its processing. It seems likely, however, that the Planck large-angular-scale polarization data analyses will be more challenging to analyze than the WMAP data because the WMAP scan strategy produces a wider range of polarization azimuth angles over more of the sky, which is an important consideration for large scale polarization measurements. WMAP data are proving to be an important and reliable calibration source for ongoing and future CMB experiments. An example of it importance is as follows: current measurements of the inflationary scalar spectral index show that ns < 1 at 2.5 s using only WMAP data, while it is 3.5 s when combining WMAP with other cosmological data. Additional operations will improve the sensitivity of the WMAP medium angular scale data, which will enable improved calibration of ACT and SPT. This, in turn, will provide strong additional constraints on ns, which will help to narrow down the allowed inflationary parameter space. 4. Conclusion Continued WMAP operations will improve measurements of both tensor modes (r) and the spectral index (ns), the two fundamental observables of inflation. If Planck achieves its design goals, the additional WMAP data will enhance the cleaning of synchrotron foregrounds in Planck. If Planck does not achieve its goals, then continued WMAP operations will be critical for large-scale polarization measurements, and for improving measurements of inflationary parameters. Either way, extended WMAP operations are a critically beneficial step in preparation for the Inflation Probe. We contend that the extended WMAP operations are important for the Inflation Probe mission, and that the most sensible time to cease WMAP observations is when the Planck mission demonstrates polarization measurements at large angular scales.