Testing Dark Energy and Gravity with Cosmological Surveys

Testing Dark Energy and Gravity with Cosmological Surveys Eric Linder 27 June 2012 UC Berkeley & Berkeley Lab Institute for the Early Universe, Korea 11

Describing Our Universe Us New Stuff Old New Stuff Us STSc. I 95% of the universe is unknown! 22

Mapping Our History The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history. STSc. I 33

Cosmic Coincidence Why not just settle for a cosmological constant ? We cannot calculate the vacuum energy to within 10120. 90 Butyears it gets Thinktoofunderstand the energywhy in For weworse: have tried 120 the asatthe level quantum At would most times is least 10 of times smaller“sea”. than we expect history, matter is either drowned or dry. –inand failed. We know there was an epoch of time varying vacuum once – inflation. Dark energy Matter Size=1/4 Size=1/2 Today Size=2 Size=4 44

On Beyond ! “You’ll be sort of surprised what there is to be found Once you go beyond and start poking around. ” – Dr. Seuss, à la “On Beyond Zebra” New quantum physics? Does nothing weigh something? Einstein’s cosmological constant, Quintessence, String theory New gravitational physics? Is nowhere somewhere? Quantum gravity, extended gravity, extra dimensions? We need to explore further frontiers in high energy physics, gravitation, and cosmology. 55

Nature of Acceleration Is dark energy static? Einstein’s cosmological constant . How do we learn what it is, not just that it is? Is dark energy dynamic? A new, time- and spacevarying field. Is dark energy a change in gravity? How much dark energy is there? DE How springy/stretchy is it? w=P/ A new law of gravity, or a new component? GN(k, z) 66

Dark Energy as a Teenager 14 years after discovery of the acceleration of the universe, where are we? From 60 Supernovae Ia at cosmic distances, we now have ~800 published distances, with better precision, better accuracy, out to z=1. 75. CMB and its lensing points to acceleration. (Didn’t even have acoustic peak in 1998. ) Das+ 2011, Sherwin+ 2011, Keisler+ 2011, van Engelen+ 2012 BAO detected. Concordant with acceleration. Weak lensing detected. Concordant with acceleration. Cluster masses (if asystematic) ~1. 5 for acceleration. Strong concordance among data: DE~0. 73, w~-1. 77

Latest Data Union 2. 1 SN Set • Complete SALT 2 reanalysis, refitting 17 data sets • 580 SNe Ia (166+414) - new z>1 SN, HST recalib • Fit Mi between sets and between low-high z • Study of set by set deviations (residuals, color) • Blind cosmology analysis! • Systematic errors as. Suzuki full covariance et al, 1105. 3470 matrix David Rubin Suzuki et al, ar. Xiv: 1105. 3470 Suzuki et al, Ap. J 2012, ar. Xiv: 1105. 3470 88

Are We Done? (stat+sys) w(z)? z<1? z>1? There is a long way to go still to say we have measured dark energy! 99

Dark Energy Properties Dark energy is very much not the search for one number, “w”. Dynamics: Theories other than give time variation w(z). Form w(z)=w 0+waz/(1+z) accurate to 0. 1% in observable. Degrees of freedom: Quintessence determines sound speed cs 2=1. Barotropic DE has cs 2(w). But generally have w(z), cs 2(z). Is DE cold (cs 2<<1)? Cold DE enhances perturbations. Persistence: Is there early DE (at z>>1)? (z. CMB)~10 -9 but observations allow 10 -2. 10 10

Beyond Einstein Gravity Expansion is not the only determiner of growth of massive structure. “The Direction of Gravity” Metric fluctuations: Anisotropic Stress/Gravitational Slip Poisson equations Energy-momentum: Euler equation δ Continuity equation v Need to know: Uzan 2006 Expansion DE perturbations Couplings Gravity 11 11

Observational Leverage Dynamics: High+low redshift, complementarity (e. g. SN+SL, SN+CMB/BAO) Degrees of freedom: Sensitivity to perturbations (CMB lensing, Galaxy clustering) Persistence: High z probes (CMB lensing, Crosscorrelate CMB x Galaxies) Test Gravity: Expansion vs growth (SN/BAO + CMBlens/Gal/WL) Very much a program: Multiple, complementary, diverse observations. Equal weighting of Theory/Simulation/Observation essential. 12 12

History of the Universe WMAP/NASA 13

Looking Back 10 Billion Years STSc. I 14 14

Our Actual Universe 15 15

Higher Dimensional Data Cosmological Revolution: From 2 D to 3 D – CMB anisotropies to tomographic surveys of density/velocity field. 16

Data, Data As wonderful as the CMB is, it is 2 -dimensional. The number of modes giving information is l(l+1) or ~10 million. BOSS (SDSS III) will map 400, 000 linear modes. Big. BOSS will map 15 million linear modes. conformal diagram SDSS I, II, 2 d. F BOSS (SDSS III) Big. BOSS 18 million galaxies z=0. 2 -1. 5 600, 000 QSOs z=1. 83 courtesy of David Schlegel N. Padmanabhan Maps of density velocity gravity 17 17

“Greatest Scientific Problem” Redshift 18 18

Cosmic Structure Galaxy 3 D distribution or power spectrum contains information on: • Growth - evolving amplitude • Matter/radiation density, H - peak turnover • Distances - baryon acoustic oscillations • Growth rate - redshift space distortions • Neutrino mass, non-Gaussianity, gravity, etc. x 25 (x 7 LRG) . . . 19 19

Baryon Acoustic Oscillations In the beginning. . . Photons tightly coupled with baryons. Density perturbations in one would cause perturbations in the other, but they couldn’t grow - merely oscillated on scales set by the sound horizon. Then swift decoupling so the perturbations were preserved. Baryon acoustic oscillations = patterned distribution of galaxies on very large scales (~150 Mpc). M. White (CMB) The same primordial imprints in the photon field show up in matter density fluctuations. Angular separation angular distance d(z) Radial distance in z expansion rate H(z) 20 20

BOSS – High Redshift, High Volume 6. 7 detection of BAO feature 1. 7% distance measurement at z=0. 57 58% complete as of 2 April 2012, 100% in July 2014 21

Big. BOSS Project 50 (Gpc/h)3 volume, z=0. 2 -3 (galaxy + Lyα) 20 million spectra, 5000 robotic fiber positioners 3 degree field M. Sholl+ 22 22

Big. BOSS Survey 3 D map of 50 (Gpc/h)3 volume with 4 M Luminous Red Galaxies, 14 M Emission Line Galaxies, 2 M Quasars Tomographic surveys of density/velocity field. 23

Redshift Space Distortions Redshift space distortions (RSD) map velocity field along line of sight. Gets at growth rate f, one less integral than growth factor (like H vs d). Ωm = gravitational growth index Hume Feldman 24 24

Redshift Space Distortions Kaiser formula inaccurate Even monopole (averaged over RSD) is poor. Anisotropic redshift distortion hopeless – without better theory. Simulation fitting function Kwan, Lewis Linder 2011 highly accurate to higher k. also see Okumura, Seljak, Mc. Donald, Desjacques 2011; Reid & White 2011 2. 5 RSD reconstruction Ptrue(k, )=F(k ) Pform(k, ) F(k ) k (h/Mpc) 0 k 25 25

CMB Probes of Acceleration How well do we really know the standard picture of radiation domination matter domination dark energy domination? Maybe acceleration is occasional. (Solve coincidence) Effect of 0. 1 e-fold of acceleration Post-recombination, peaks left and adds ISW. Pre-recombination, peaks right and adds SW. Current acceleration unique within last factor 100, 000 of cosmic expansion! Linder & Smith 2010 26 26

Beyond GR Functions Test gravity in model independent way. Gravity and growth: Gravity and acceleration: Are and the same? (yes, in GR) Tie to observations via modified Poisson equations: Glight tests how light responds to gravity: central to lensing and integrated Sachs-Wolfe. Gmatter tests how matter responds to gravity: central to growth and velocities ( is closely related). 27 27

Big. BOSS Leverage low k, low z Glight-1 low k, high z Daniel & Linder 2012 high k, low z Glight-1 high k, high z current +WL Big. BOSS Pk Gmatter-1 5 -10% test of 8 parameters of model-independent gravity. 28

Fundamental and Primordial Physics Massive neutrinos free stream, damping the matter power on small scales. Long lever arm in k determines Σm to 0. 02 e. V. Long range in k tests running of primordial spectrum. Large scales test non-Gaussianity. Both are probes of inflation. 29

Summary Much progress already made. Dark energy is not the search for one number “w”. Explore dynamics, degrees of freedom, persistence. Galaxy redshift surveys 3 D maps of density/velocity fields, measuring expansion, growth, and gravity (also measures mν, non-Gaussianity, inflation). CMB polarization lensing is an upcoming probe. Data in next 5 years has us closing in on our chase of cosmic acceleration. New theories for the origin of cosmic acceleration? 30 30