COSMOLOGY AS A TOOL FOR PARTICLE PHYSICS Roberto Trotta University of Oxford Astrophysics & Royal Astronomical Society
Vol. 302, 12/2003 «Cosmos Sits for Early Portrait, Gives Up Secrets » Feb. 12 th, 2003
Outline Towards precision cosmology Neutrino properties from high quality cosmological observations Conclusions & Outlook
Cosmological observables s 3 mins 300’000 yrs 1 Gyr 13 Gyrs Gravitational waves BBN Cosmic Neutrino Background Supernovae Type Ia GRB’s Sunyaev Zel’dovich Cosmic Microwave Background Large Scale Structures Lensing Ly- systems Clusters counts
The Cosmic Microwave Background Temperature fluctuation on the 2-sphere: 2-point correlation function: Temperature power spectrum
Cosmology with the CMB The statistical distribution of temperature anisotropies described by the 2-point angular correlation function, or equivalently by the angular power spectrum For Gaussian fluctuations (as predicted by inflation), the power spectrum contains the full statistical information. Small fluctuations ) linear perturbation theory sufficient. The power spectrum carries characteristic signatures of interesting physical quantities: baryon density angular diameter distance (“curvature”) matter-to-relativistic energy ratio damping scale (diffusion length) 1st peak position (WMAP)
Cosmological Params (May 05) Degeneracy breaking crucial Combining CMB + SDSS + HST + SNIa Posterior probability
Inflationary paradigm B-polarization smoking gun ! Direct detection: LIGO, Virgo, LISA Flatness tot = 1.02 § 0.02 Bayesian evidence 18 : 1 Non-Gaussianity-58 < f nl < 134 inflation » curvaton » 1 Planck (2007) > 5 Non-adiabaticity isocurvature < 33% Bayesian evidence > 1000 : 1 in favor of adiabatic pert’ons Scale invariance n s = 0.95 § 0.03 Planck (2007): 90% chance of disproving scale invariance with high evidence Gravity waves ? r 10 < 0.35 E inf < M pl
The hidden assumptions BBN b » HST 0.72 § 0.08 Assumptions about initial fluctuations crucial for precision cosmology RT, Riazuelo & Durrer (2001) RT & Durrer (2004) Beltran et al (2004) Precision cosmology: < 2% error on most parameters Pre-WMAP (2001), but still qualitatively the case Polarization saves the day
Exploring the cosmic neutrino background
What good is cosmology? Impact of (light) neutrinos on cosmological observables: Background: relativistic energy drives expansion early on Clustering / structure formation: free stream properties (mass/viscosity/couplings) Initial conditions: isocurvature (entropy) perturbations log log a = const rad ~ a - 4 mat ~ a - 3 time radiation dominated matter dominated lambda dominated
Massless families CERN, 1991: N = § WMAP+ : 2.4 < N < 6.8 (2 ) BBN : 2.8 < N < 3.2 Matter/radiation equality affected
Neutrino masses Mass hierarchy: m 12 2 » 8 x eV 2 m 23 2 » 2.6 x eV 2 Absolute mass: Tritium decay m e < 2.3 eV (95% cl) Cosmology : m < O(1) eV Structure washed out below scales k nr » (m ) 1/2 ( m h 2 ) 1/2 While relativistic, neutrinos free-stream out of fluctuations Hu, Eisenstein & Tegmark 1998
Detecting the CNB c vis 2 = 1/3 : radiative viscosity free streaming c vis 2 = 0 : perfect fluid no anisotropic stress (eg, CDM coupling) acoustic oscillations Viscosity parameter c vis 2 : controls the free-streaming behaviour Hu 1998 RT & Melchiorri 2004
Positive evidence for a CNB CMB + SLOAN c vis 2 = 0 clearly disfavored (about 2 Bayesian model comparison: c vis 2 = 1/3 favored with odds 2:1 CMB+SDSS CMB alone CMB+SDSS CMB alone +BBN Assuming N = 3 RT & Melchiorri 2004
Automatic Occam’s razor CNB RT 2005 Model comparison tools to assess the need for new parameters 00 Mismatch with prediction n s : scale invariance : flatness f iso : adiabaticity
Prospects for precision cosmology Temperature alone Polarization alone Almost orthogonal degeneracies Polarization lifts flat directions in Temperature Constraints improve significantly Many polarization-dedicated experiments upcoming ( ): POLARBEAR (2005): 100 < ell < 1400 QUEST (2005): 100 < ell < 1000 Bicep (2005): 10 < ell < 1000 SPOrt (ISS, 2005?): full sky Planck (2007): up to ell = 2000
Conclusions and Outlook data-driven field Cosmology is a data-driven field with much more to come Moving on from parameter fitting to model testing and model selection Combination of data-sets allows cross-validation and checks of systematics Subtle physics of the Concordance Model and beyond being stringently tested. Expect advances on dark energy/matter- neutrinos, dark energy/matter, brane-worlds, cosmic strings, topology, axis of evil (?) Watch out for: high quality polarization data, lensing, correlations between observations, high quality polarization data, lensing, GW