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The Future of the CMB Marc Kamionkowski (Caltech) AIU ’08, Tsukuba, 13 March 2008 CMB that we see originates from edge of observable Universe as it was ~400,000 years after the big bang, ~14 billion years ago You are here 14 billion light-years Causally connected region Observe: •CMB smooth to 1st approximation •Has small fluctuations •BBN accounts for light-element abundances Can infer: •Primordial density perturbations exist •Have small amplitude on largest scales •Have small amplitude on smallest scales •Have spectrum (in wavenumber k) no steeper than scale invariant Slow-roll parameters Inflationary perturbations: (open) (flat) First test of inflation: Is the Universe flat? T(n)=Σ almYlm(n) Cl=<|alm|2> CMB determination of the geometry (MK, Spergel, and Sugiyama, 1994) YES! 30 mK BOOMERanG (2002) Now even more precise from WMAP Cosmological-parameter determination (Jungman, MK, Kosowsky, Spergel 1996) WMAP-3: even better than we expected!! WHAT NEXT??? GEOMETRY SMOOTHNESS STRUCTURE FORMATION INFLATION What is Einfl? STOCHASTIC GRAVITATIONAL WAVE BACKGROUND with amplitude Einfl2 Detection of ultra-long-wavelength GWs from inflation: use plasma at CMB surface of last scatter as sphere of test masses. Temperature pattern produced by one gravitational wave oriented in z direction z No Gravity Waves Gravity Waves Detection of gravitational waves with CMB polarization (MK, Kosowsky, Stebbins, 1996; Seljak & Zaldarriaga 1996) Temperature map: “E Mode” Polarization Map: Density perturbations have no handedness” “B so they cannot produce a polarization with a curl mode” Gravitational waves do have a handedness, so they can (and do) produce a curl Model-independent probe of gravitational waves! “Curl-free” polarization patterns “curl” patterns Recall, GW amplitude is Einfl2 l2 GWs T And from COBE, Einfl<3x1016 GeV GWs unique polarization pattern. Is it detectable? If E<<1015 GeV (e.g., if inflation from PQSB), then polarization far too small to ever be detected. But, if E~1015-16 GeV (i.e., if inflation has something to do with GUTs), then polarization signal is conceivably detectable by Planck or realistic post-Planck experiment!!! Big news: If ns=0.95, and ε~η (and no weird cancellation), then ε~0.01, V~(2x1016 GeV)4, and r=T/S~0.1. I.e., GW background ~ “optimistic” estimates (e.g., Smith, Cooray,MK, arXiv:0802:1530) WMAP BICEP QUIET1 QUEST (QUaD) Planck QUIET2 Hivon SPIDER (Kesden, Cooray, MK 2002; Knox, Song 2002) If GW amplitude small, may need high-resolution T/P maps to disentangle cosmic-shear contribution to curl component from that due to inflationary gravitational waves. Lensing shifts position on sky: Where the projected grav potential is and so lensing induces a curl even if there was no primordial curl, with power spectrum How can we correct for it? T also lensed. In absence of lensing, but with lensing, We can therefore reconstruct the deflection angle…. Another possibility to correct for cosmic shear (Sigurdson, Cooray 2005) • Use 21-cm probes of hydrogen distribution to map mass distribution between here and z=1100 The CMB: What else is it good for? WMAP-5: fraction of CMB photons that re-scattered after recombination (z~1100) is τ~0.1. If electrons that re-scattered these CMB CMB photons were ionized by radiation from the first stars, then the first stars formed at z=10 Probes of parity violation in CMB (Lue, Wang, MK 1999) Might new physics responsible for inflation be parity violating? TC and TG correlations in CMB are parity violating. Can be driven, e.g., by terms of form during inflation or since recombination WMAP search: Feng et al., astro-ph/0601095 Komsatsu et al. (WMAP-5) High-frequency gravitational waves and the CMB GWs are tensor modes of perturbations. “Conventional” way to probe GWs: 1) low-l plateau versus peaks 2) B mode polarization New approach: Small scale GW behave as massless particles. They contribute to the energy density of the Universe. Limits on gravitational-wave energy density Smith, Pierpaoli, MK (PRL, 2006) Particle Decays and the CMB Xuelei Chen and MK, PRD 70, 043502 (2004) L. Zhang et al., PRD 76, 061301 (2007) also, Kasuya, Kawasaki, Sugiyama (2004) and Pierpaoli (2004) • Can we constrain dark-matter decay channels and lifetimes from the CMB and elsewhere? Photons absorbed by IGM Transparency window IGM optical depth, temperature, and ionization for decaying particle Ionization induced by particle Decays affects CMB power spectra What Else?? Inflation predicts distribution of primordial density perturbations is Gaussian (e.g., Wang &MK, 2000). But how do we tell if primordial perturbations were Gaussian?? In single-field slow-roll inflation, nongaussianity parameter (e.g., Wang-MK 1999): fNL ~ ε (δρ/ρ) ~ 0.01 x 10-5 Will be small!! WMAP now at fNL ~50; Planck to get to fNL ~O(1). So simplest models not to be tested, but alternatives may produce larger fNL . Gaussian random field Φ=φ+ fNL (φ2-<φ2>) Gravitational potential How do we tell if primordial perturbations were Gaussian?? (1) With the CMB: Advantage: see primordial perturbation directly Disadvantage: perturbations are small T/T How do we tell if primordial perturbations were Gaussian?? (2) With galaxy surveys: Advantage: perturbations are bigger Disadvantage: gravitational infall induces non-Gaussianity (as may biasing) Evolved Primordial How do we tell if primordial perturbations were Gaussian?? (3) With abundances of clusters (e.g., Robinson, Gawiser & Silk 2000) or high-redshift galaxies (e.g., Matarrese, Verde & Jimenez 2000): Rare objects form here How do we tell if primordial perturbations were Gaussian?? (4) With distribution of cluster sizes (Verde, MK, Mohr & Benson, MNRAS, 2001): Broader distribution of >3 peaks leads to broader formation redshift distribution and thus to broader size distribution How do we tell if primordial perturbations were Gaussian?? How do these different avenues compare? For just about any nonGaussianity with long range correlations (e.g., from topological defects or funny inflation), CMB> LSS (Verde, Wang, Heavens & MK, 2000). Cluster and high z abundances do better at probing nonGaussianity from topological defects than CMB/LSS, while CMB remains best probe of that from funny inflation (Verde, Jimenez, Matarrese & MK, MNRAS 2001). Is the Universe Statistically Isotropic? Pullen and MK, PRD (2007); Ando and MK PRL (2008) Inflation usually predicts primordial perturbations are statistically isotropic---they have no preferred direction: Power spectrum P(k) function of wavenumber k magnitude only; not its direction. But what if this were violated (e.g., Ackerman, Carroll,Wise, 2007)? What if we had a power spectrum that depended on the direction of k? Statistically isotropic E.g., a power quadrupole If SI is violated: And is straightforward to calculate the Dll’ given P(k). Departures from SI correlate different alm’s. Pullen-MK: minimum-variance estimators for the ξlml’m’ and also the gLM. E.g., WMAP sensitive to g20~0.02 and Planck to g20~0.005 (1σ). Ando-MK: nonlinear evolution of primordial anisotropic power: Pprim(k) Ptoday(k) required to search galaxy surveys for SI departures. Pullen-Hirata now testing SI with SDSS/WMAP Direct Detection of Inflationary Gravitational Waves? (T. L. Smith, MK, Cooray, PRD 2006; see also Efstathiou-Chongchitnan and Smith-Peiris-Cooray) Mission concept studies: •NASA: Big-Bang Observer (BBO) •Japan: Deci-Hertz Gravitational-Wave Observatory (DECIGO) seek to detect directly inflationary gravitationalwave background at ~0.1-Hz frequencies Survey some “toy” models for inflation: “power-law” “chaotic” “hybrid” “symmetry-breaking” Tensor-to-scalar ratio r chaotic Power-law Symmetry breaking chaotic For dessert: something completely different….. Dark Matter, the Equivalence Principle, and Dwarf Galaxies Work done with Mike Kesden, PRL 97, 131303 (2006) [astro-ph/0606566], PRD 74, 083007 (2006) [astro-ph/0608095] observed 3-5 kpc dis k Local dark-matter 8.5 kpc density: ~0.4 (GeV/c2)/cm3 Velocity dispersion: v ~ 300 km/sec But does dark matter fall same way in gravitational field? Does the force law, hold for dark matter as well? And if how would we know? Instead, consider tidal streams of Sagittarius dwarf: •Sgr is DM dominated so acts as DM tracer of Milky Way potential, while stripped stars act as baryonic tracers. •Streams are long-lived and now well-observed with 2MASS and SDSS •Detailed simulations compared with observations already provide remarkably precise constraints to Sgr mass, M/L, orbit, and Milky Way halo (e.g., Law, Johnston, Majewski 2005) Majewski et al. 2003 Where do tidal streams come from? MW trajectory M=mass R Trailing tail Sgr r m=mass Leading tail Where do tidal streams come from? MW trajectory M=mass R Trailing tail Sgr r m=mass Leading tail Conclusions • Conservative “by-eye” comparison with observation of roughly equal leading and trailing stream constrains DM force law to be within ~10% of that for baryons Summary • CMB provides ever increasing evidence for inflation • Departure from scale invariance significant, if real, provides additional motivation for pursuing IGWs • Cosmic shear of CMB provides exciting new target; room for theoretical and data-analysis work • Can begin to test Gaussianity of primordial perturbations • Can begin to test validity of statistical-isotropy prediction • Theorists need to be more imaginative: what else can we do with the CMB? Where do we go next?