Published on November 15, 2007
Recent & FutureDevelopments in Cosmology: Recent & Future Developments in Cosmology Josh Frieman XXII Physics in Collision, Stanford, June 2002 Concordance Cosmology: Concordance Cosmology Our knowledge of the cosmological parameters has made tremendous strides in the last two years: b = 0.04 (to ~20%) baryons m = 0.3 (to ~20%) matter DE = 0.7 (~15%) dark energy total = 1 (~5%) ns = 1 (~10%) slope of power spectrum H0 = 72 km/sec/Mpc (~10%) HST Key Project t0 = 14 Gyr (~8%) The prospects for increasing the precision of these measurements in the near future are excellent. Some Key Questions for 21st Century Cosmology: Some Key Questions for 21st Century Cosmology Did inflation occur in the early Universe, and did it originate the perturbations that formed Large-scale structure? What is the nature of the Dark Matter that makes up most of the mass of the Universe? What is the nature of the Dark Energy that is causing the expansion of the Universe to accelerate? What happened `before’ the Big Bang? Is this question meaningful? Are there more than 3 spatial dimensions? Can we ever detect them? The Structure Formation Cookbook: The Structure Formation Cookbook 1. Initial Conditions: A Theory for the Origin of Density Perturbations in the Early Universe Your favorite Inflation model: primordial spectrum P ~ kn 2. Cooking with Gravity: Growing Perturbations to Form Structure Set the Oven to Cold (or Hot or Warm) Dark Matter Season with a few Baryons and add Dark Energy 3. Let Cool for 13 Billion years 4. Tweak (1) and (2) until it tastes like the observed Universe. Slide5: BBN Theory vs. Observations: Remarkable agreement over 10 orders of mag. in abundance variation Concordance region: b h2 = 0.020 0.002 h=0.7 b = 0.04 Strongest constraint from Deuterium in QSOALS. Burles, etal 4He b Slide6: Dependence of CMB anisotropy on the baryon density Angular separation on the sky CMB Temp. Angular Power Spectrum Slide7: Recent CMB Anisotropy Experiments: South Pole Boomerang DASI Slide8: Going to smaller angular scales: higher resolution Microwave Background AnisotropyProbes the Baryon Density: Microwave Background Anisotropy Probes the Baryon Density Boomerang (2001) Wbh2 = 0.022 0.0035 DASI (2001) Slide10: Testing CDM Models: Mass Power Spectrum Amplitude 8 Rms Linear Mass Fluctuations in spheres of Radius 8h-1 Mpc SCDM CDM O(pen)CDM P ~ k P ~ k-3 keq ~ mh = shape h/Mpc Non-linear Linear Slide11: Probing Neutrino Mass and Baryon Density with LSS SDSS + MAP: will constrain sum of stable neutrino masses as low as ~ 0.5 eV Wiggles Due to Non-zero Baryon Density Slide13: Constraints on the Baryon Density from 2dF Galaxy Redshift Survey Power Spectrum Percival, etal. Tegmark & Hamilton Increasing b suppresses power on small scales (and increases amplitude of wiggles) Slide14: 2dF GRS Power Spectrum m,tot < 2.2 eV --reasonable prior on m --BBN prior on b --simple model of bias & redshift distortions Elgaroy, etal =0 0.01 0.05 = m,tot 94 eV Slide15: Pryke Slide16: Angular Position of first Peak probes spatial Curvature of the Universe Hu Microwave Background AnisotropyProbes Spatial Curvature : Microwave Background Anisotropy Probes Spatial Curvature Boomerang (2001) DASI (2001) W0 = 1.03 0.06 W0 = 1.04 0.06 Data consistent with Flat spatial sections (expected from inflation) Recent CBI Results: Recent CBI Results --consistent with previous experiments at low l --expected damping to l = 2000 (viscosity+finite thickness of last-scattering surface) Slide19: Bond, etal Inflation predicts nearly Scale- invariant primordial fluctuations (ns 1) Combined Likelihood: CMB + LSS Slide21: CBI Excess Power at l > 2000? 3 effect Could be due to Sunyaev-Zel’dovich Effect (Compton scattering of CMB by hot gas in clusters) Requires high normalization of P(k): 8 ~ 1.0 Cl ~ 87 Probes of the Matter Density m: Probes of the Matter Density m Slide23: m from recent CMB experiments: height of first peak m h2 = 0.16 ± 0.04 Note: relies on assumptions about gravity waves (tensor modes) from inflation Bridle, etal Slide24: CMB Sky: 1992 circa Jan. 2003 (release of MAP 1-year data) Slide25: MAP Satellite launched June 2001 High Precision Measures of Cosmo. parameters Planck Satellite planned for ~2008 Evidence for Inflation: Evidence for Inflation Large-scale homogeneity and isotropy (by design) Spatial flatness (Euclidean): total = 1 Power Spectrum of density perturbations inferred from CMB experiments agrees to high precision with spectrum predicted by inflation: n 1 Future: more precise measurements by satellites (MAP, Planck) measurement of CMB polarization test inflationary prediction for gravity wave spectrum and distinguish between inflation models The search for CMB polarization: The search for CMB polarization Near term (2002-3): detection of polarization (E modes) Long term: detection of `B modes’ gravity waves Early discussions of a dedicated NASA polarization mission Slide28: MAP 1- errors Slide29: Relative Amplitude Of tensor Perturbations Slide30: Statistical accuracy of Power spectrum from Completed SDSS Redshift Survey Assuming 900,000 galaxies in Main galaxy sample (flux-limited) 100,000 Luminous Red Galaxies (color/photo-z selected) Cold Dark Matter Models mh=0.5 SCDM mh=0.2 CDM (assumed biased) Slide31: SDSS 2.5 meter Telescope Slide32: Galaxy Clustering in the SDSS Redshift Survey ~100,000 galaxies Voids, sheets, filaments Slide33: SDSS Angular Clustering Galaxy angular correlation function dP=n2[wdd Check for systematics: correlate with dust, galactic latitude, seeing Mask out regions of bad seeing, high dust obscuration, bright stars, etc. Careful error analysis: covariance Scranton, etal Connolly, etal bright faint Slide34: Safe Truncation of KL modes Orthogonal Constraints Probing Power Around the Peak Amplitude 8 = 0.92 ± 0.06 Shape ( mh) = 0.19 ± 0.04 Two-parameter fit of SDSS Angular KL Data to CDM Models Szalay, etal Slide35: Galaxy Power Spectrum (SDSS Redshift Space: preliminary) Slide36: Caveat: Galaxies are Biased tracers of the Dark Matter Bias is usually assumed scale- independent at small k Tegmark, etal Slide37: Caveat: Galaxy Clustering varies with Galaxy Type How are each of them related to the underlying Mass distribution? Bias depends upon Galaxy Type Need large, carefully selected samples to study this: SDSS, 2dF Slide38: Is Bias scale- independent in the Linear regime? Slide39: Bias Depends on Galaxy Color Cf. morphology- density relation Zehavi, etal SDSS Redshift Survey Slide40: Bias depends on Galaxy Luminosity Compare 2dF results of Norberg, etal Intrinsically bright Intrinsically faint SDSS Redshift Survey Slide41: Gravitational Lensing by Clusters of Galaxies `giant arcs’: galaxies behind the cluster, gravitationally lensed Slide42: Large-scale Weak Lensing: Cosmic Shear Correlations directly probe Mass distribution Signal Systematic error Van Waerbeke, etal Slide43: Constraints from Weak Lensing & from Cluster Abundances Slide44: Constraints from CMB & Weak Lensing CMB Large Synoptic Survey Telescope : Large Synoptic Survey Telescope Proposed 8.5m ground based telescope with 7 sq. degree field 5000 Gbytes/night Real-time analysis “Celestial Cinematography” Also: SNAP, VISTA, PANSTARRS,… The Future of Weak Lensing: Slide46: LSST Weak Lensing Map of Mass Power Spectrum Hu Cluster Probes of the Matter Density: Wm: Cluster Probes of the Matter Density: Wm Current evidence: Galaxy kinematics Cluster baryons fb ~ 10-20% Wb h2 = 0.02 (BBN/CMB) Wm ~ 0.2-0.4 X-ray gas Lensing Wm ~ 0.3 The Two Dark Matter Problems: The Two Dark Matter Problems Observations indicate: visible matter ~ 0.01 baryons ~ 0.04 dark matter ~ 0.3 Dark Baryonic matter Dominant component of Dark Matter is Non-baryonic BBN+CMB Slide49: Recent results from Direct WIMP Searches CDMS II now being installed in Soudan gain factor 100 in sensitivity Gaitskell preliminary Slide50: Does Cold Dark Matter predict too much substructure in Galaxy Halos? Hierarchical Merging Dwarf Satellites of the Local Group Moore Slide51: Satellites of the Local Group observed predicted Clumps which form stars before reionization at z = 10 Slide52: Red: particles in halos that cool before z = 10 Slide53: F (main sequence turnoff) stars on the celestial equator from SDSS Debris From Sagittarius Dwarf Galaxy New Structures In the Milky Way Halo A C Slide54: Stiff, Widrow, JF Halo Substructure and Direct Cold Dark Matter Detection Simulated CDM Clumps & Tidal Streams are coherent in Velocity space Signature of Local Clump/Stream in WIMP Recoil Energy Spectrum Slide55: Halo Substructure and Indirect WIMP Detection Neutralino Annihilation in halo subclumps signal in EGRET, GLAST, VERITAS,… + synchroton signal in CMB Blasi, Olinto, Aloisio (also Bergstrom, etal, Calcaneo-Roldan & Moore) Slide56: EGRET diffuse Background constrains subclump inner density profiles & annihilation cross-sections 100 GeV 1 TeV ~ r–2 SIS ~ r–1.5 Moore ~ r–1 NFW GLAST: anisotropic signal Slide57: Tasitsiomi & Olinto VERITAS: S/N = 5 Limits for 100 hours Dark Energy and the Accelerating Universe: Dark Energy and the Accelerating Universe Brightness of distant Type Ia supernovae indicates the expansion of the Universe is accelerating, not decelerating. If General Relativity is valid, this requires a new form of stress-energy-momentum with negative effective pressure*: DARK ENERGY Characterize by its equation of state: w = p/ *more specifically, p < (w < 1/3) Dubya Evidence for Dark Energy: Evidence for Dark Energy Direct Evidence for Acceleration Brightness of distant Type Ia supernovae: Standard candles measure luminosity distance dL(z): sensitive to the expansion history H(z) Supernova Cosmology Project High-Z Supernova Team II. Evidence for `Missing Energy’ CMB Flat Universe: 0 = 1 Clusters, LSS, CMB Low matter density m 0.3 missing = 1 – 0.3 = 0.7 and missing stuff can only dominate recently for structure to form: w < – 0.5 Tragic (Pre-)History of Dark Energy:a cautionary tale: Tragic (Pre-)History of Dark Energy: a cautionary tale Cosmological constant has been periodically invoked to solve cosmological crises, then dropped when they passed: 1916: Einstein: static Universe (`greatest blunder of my life’) 1929: 1st `age crisis’: Universe (t ~1/H) younger than Earth 1967: apparent clustering of QSOs at fixed redshift 1974: luminosity distance using galaxy std. candles acceleration 1995: 2nd ‘age crisis’: H0 = 80 km/sec/Mpc; U. younger than globular clusters 1998: luminosity distance using Sne Ia std. candles acceleration 2000: Spatial flatness from CMB anisotropy Missing energy Slide62: Given this tawdry history, why should we take Dark Energy seriously now? 1. No killer systematic errors for SNe Ia yet identified. 2. For the first time, we now have multiple lines of evidence pointing to Dark Energy, each subject to different systematic errors Slide63: Type Ia Supernovae Peak Brightness as a calibrated `Standard’ Candle Intrinsic Brightness vs. Time Physical model: White dwarf star, accreting mass from a companion star, explodes when it exceeds a critical mass (Chandrasekhar) Luminosity Time Slide64: m(z) = M+5log(H0dL)=(1+z) dz’/H(z’) Apparent Brightness Fainter 42 SNe Ia Slide65: Assuming w = 1 Consistent results from High-Z Team Riess, etal ‘98 Type Ia Supernovae: Type Ia Supernovae Advantages: small dispersion in peak brightness (std. candles) single objects (simpler than galaxies) can be observed over wide z range Challenges: dust (grey dust) causing distant SNe to appear fainter chemical composition evolution of progenitor population photometric calibration environmental differences Continuing Evidence for Acceleration: Continuing Evidence for Acceleration Riess et al. (2001) SN 1997ff NICMOS (HST) serendipitous discovery z = 1.7 (m-M) CMB and Supernovae: CMB and Supernovae Wm = 0.27 0.13 WL = 0.72 0.11 de Bernardis et al (2001) Bridle etal (2002) orthogonal constraints SNe CMB CMB + H0 CMB+H+SN +2dF+clusters Slide70: m DE w w w w Garnavich etal Slide72: SNe + Clusters (m > 0.2) w < 0.65 (1) Slide73: Perlmutter, Turner, White ‘99 Bean, etal ‘01 Combine Constraints Age of the Universe: Age of the Universe H0 = 72 8 km/sec/Mpc (Freedman et al. 2001) t0 = 13 1.5 Gyr (Chaboyer 2001, Krauss 2000) H0 t0 = 0.93 0.15 w < -0.5 H0t0 0.25 0.35 Wm H0r/H0t0 Huterer & Turner 2001 Dark Energy Models?: Dark Energy Models? Cosmological Constant: Vacuum Energy (w = -1) Dynamical scalar fields (w varies) (aka `quintessence’ east of the Delaware River) Frustrated topological defects (w = -1/3 or –2/3) Replace General Relativity (extra dimensions?) Two Problems: Two Problems Cosmological constant problem: why is the vacuum energy density 40-120 orders of magnitude smaller than expected? Coincidence problem: why do we live at the special epoch when the vacuum energy density is comparable to the matter energy density? matter ~ a-3 DE ~ a-3(1+w) vac = constant matter DE a Slide77: These two problems are common to ALL Dark Energy models All Dark Energy models assume a (benign) solution of the Cosmological Constant problem Dynamical Scalar Field Modelsaka Quintessence: Dynamical Scalar Field Models aka Quintessence Ultra-light particle: Dark Energy hardly clusters, nearly smooth Equation of state: in general, w > -1 and evolves in time Hierarchy problem: Why m/ ~ 10-61? General features: meff < 3H0 ~ 10-33 eV (w < 0) (Potential vs. Kinetic Energy) ~ m22 ~ crit ~ 10-10 eV4 ~ 1028 eV ~ MPlanck Dynamical Scalar Field Modelsaka Quintessence: Dynamical Scalar Field Models aka Quintessence Runaway potentials DE/matter constant (Tracker Solution) but coincidence and hierarchy problems remain Pseudo-Nambu Goldstone Boson: Low mass protected by symmetry (ala axion) Frieman, etal V() = M4[1+cos(/f)] f ~ Mplanck M ~ 0.001 eV Key Issues for the Decade: Key Issues for the Decade Is there Dark Energy? Will the SNe results hold up? What is the nature of the Dark Energy? Is it or something else? How does w = pX/X evolve? Dark Energy dynamics Theory Slide81: Proposed satellite mission to observe several thousand SNe out to z ~ 1.7 and bring systematics under control Slide82: Goliath, etal Physical Effects of Dark Energy: Physical Effects of Dark Energy Dark Energy affects expansion rate of the Universe: Dark Energy may also interact: long-range forces Carroll Slide84: Comoving Distance: r(z) = dx/H(x) In a flat Universe: Luminosity Distance: dL(z) = r(z)(1+z) Angular diameter Distance: dA(z) = r(z)/(1+z) Comoving Volume Element: dV/dzd = r2(z)/H(z) Physical Observables: probing DE: Physical Observables: probing DE 1. Luminosity distance vs. redshift: dL(z) m(z) Standard candles: SNe Ia 2. Angular diameter distance vs. z: dA(z) Alcock-Paczynski test: Ly-alpha forest; redshift correlations 3. Number counts vs. redshift: N(M,z) probes: *Comoving Volume element dV/dzd *Growth rate of density perturbations (z) Counts of galaxy halos and of clusters; QSO lensing Slide86: Sensitivity to Dark Energy equation of state Volume element Comoving distance Huterer & Turner Slide87: Projected SNAP Sensitivity to DE Equation of State Slide89: What is the optimal SNe Ia redshift distribution, given information from future CMB missions? Do we need to go to high redshift? Yes Huterer, Linder, Turner, JF Slide90: SNAP Sensitivity to Varying DE Equation of State w(z) = w0 + w1z + ... Slide92: Sloan Digital Sky Survey Projected constraints from redshift space clustering of 100,000 Luminous Red Galaxies (z ~ 0.4) Matsubara & Szalay Slide93: Volume Element as a function of w Dark Energy More volume at moderate redshift Slide94: Counting Galaxy Dark Matter Halos with the DEEP Redshift Survey Newman & Davis Huterer & Turner 10,000 galaxies at z ~ 1 with measured linewidths (rotation speeds) NB: must probe Dark matter- dominated regions Slide95: Growth of Density Perturbations Holder Open or w > -1 Flat, matter-dominated Counting Clusters of Galaxies: Counting Clusters of Galaxies Sunyaev Zel’dovich effect X-ray emission from cluster gas Weak Lensing Simulations: growth factor Slide97: Haiman, Holder, Mohr Detection Mass thresholds Slide98: Expected Cluster Counts in a Deep, wide Sunyaev Zel’dovich Survey Holder, Carlstrom, etal Slide99: Constraints from a 4000 sq. deg. SZE Survey Mlim = 2.5 x 1014 h-1 Msun Holder, Haiman, Mohr Slide100: Abell 3667 Weak Lensing Mass Map z = 0.05 Joffre, etal Slide101: R ~ 27.5; 20,000 sq. deg. (co-added LSST or 1-year wide-field SNAP) R ~ 30; 16 sq. deg. R ~ 25, 200 sq. deg (SDSS south) Number of Clusters detected by Weak Lensing (nominal SNAP in SNe mode) Joffre, JF Slide102: Cluster Weak Lensing Conclusions: Conclusions Precision cosmology is bringing sharply into focus the fundamental physics issues underlying the values of the cosmological parameters Although 20th C. cosmology is littered with false prophets of , for the first time we have multiple lines of evidence for Dark Energy Nature of the Dark Energy remains a mystery, wrapped in the larger enigma of the Cosmological Constant problem. Theorists are stumped, but the prospects for probing the Dark Energy using multiple nearly `orthogonal’ observational techniques are very good over the coming decade. These probes are needed to blaze the trail for fundamental theory.