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

10 -32 s 3 mins Gravitational waves Cosmic Neutrino Background BBN 300’000 yrs Cosmic Microwave Background 1 Gyr Large Scale Structures Lensing Ly  systems Clusters counts 13 Gyrs Supernovae Type Ia GRB’s Sunyaev Zel’dovich

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.

1st peak position (WMAP) 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)

Cosmological Params (May 05)

Combining CMB + SDSS + HST + SNIa Degeneracy breaking crucial

Flatness Non-Gaussianity Non-adiabaticity Scale invariance Gravity waves ?

Inflationary paradigm

 tot = 1.02 § 0.02

Bayesian evidence 18 : 1 -58 < f nl < 134 inflation curvaton

» »

10 -5 1 Planck (2007) > 5 isocurvature < 33% Bayesian evidence > 1000 : 1 in favor of adiabatic pert’ons n s = 0.95 § 0.03

Planck (2007): 90% chance of disproving scale invariance with high evidence r 10 < 0.35

E inf < 10 -5 M pl B-polarization smoking gun !

Direct detection: LIGO, Virgo, LISA

The hidden assumptions

Assumptions about initial fluctuations crucial for precision cosmology BBN  b

»

0.022

HST 0.72

§ 0.08

RT, Riazuelo & Durrer (2001) RT & Durrer (2004) Beltran et al (2004) Polarization saves the day Pre-WMAP (2001), but still qualitatively the case Precision cosmology: < 2% error on most parameters

Exploring the cosmic neutrino background

What good is cosmology?

Impact of (light) neutrinos on cosmological observables: log r Background: relativistic energy drives expansion early on Clustering / structure formation: free stream properties (mass/viscosity/couplings) Initial conditions: isocurvature (entropy) perturbations r rad ~ a - 4 time r mat ~ a - 3 r L = const radiation dominated matter dominated lambda dominated log a

Massless families

Matter/radiation equality affected CERN, 1991: N  = 2.994 § 0.012 WMAP+ : 2.4 < N  BBN : 2.8 < N  < 3.2

< 6.8 (2  )

While relativistic, neutrinos free-stream out of fluctuations

Neutrino masses

Structure washed out below scales k nr » (m  ) 1/2 (  m h 2 ) 1/2 Mass hierarchy:  m 12 2 » 8 x 10 -5 eV 2  m 23 2 » 2.6 x 10 -3 eV 2 Absolute mass: Tritium decay m  e < 2.3 eV (95% cl) Cosmology :   m  < O(1) eV Hu, Eisenstein & Tegmark 1998

Detecting the CNB

Viscosity parameter c vis 2 : controls the free-streaming behaviour c vis 2 = 1/3 : radiative viscosity free streaming c vis 2 = 0 : perfect fluid no anisotropic stress (eg,   CDM coupling) acoustic oscillations Hu 1998 RT & Melchiorri 2004

Positive evidence for a CNB

Assuming N  = 3 CMB alone CMB+SDSS CMB+SDSS CMB alone +BBN CMB + SLOAN c vis 2 = 0 clearly disfavored (about 2 ) Bayesian model comparison: c vis 2 = 1/3 favored with odds 2:1 RT & Melchiorri 2004

Automatic Occam’s razor

Model comparison tools to assess the need for new parameters CNB  0 RT 2005 n s : scale invariance   : flatness f iso : adiabaticity 

Prospects for precision cosmology

Almost orthogonal degeneracies Polarization lifts flat directions in Temperature Constraints improve significantly Temperature alone Polarization alone Many polarization-dedicated experiments upcoming (2005-07): 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

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 neutrinos, dark energy/matter, brane-worlds, cosmic strings, topology, axis of evil (?) Watch out for: correlations between observations, high quality polarization data, lensing, GW