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COSMOLOGY AS A TOOL FOR PARTICLE PHYSICS

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

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COSMOLOGY AS A TOOL FOR PARTICLE PHYSICS

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  1. COSMOLOGY AS A TOOL FOR PARTICLE PHYSICS Roberto Trotta University of Oxford Astrophysics & Royal Astronomical Society

  2. Vol. 302, 12/2003 «Cosmos Sits for Early Portrait, Gives Up Secrets» Feb. 12th, 2003

  3. Outline • Towards precision cosmology • Neutrino properties from high quality cosmological observations • Conclusions & Outlook

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

  5. The Cosmic Microwave Background • Temperature fluctuation on the 2-sphere: • 2-point correlation function: • Temperature power spectrum

  6. Cosmology with the CMB 1st peak position (WMAP) • 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) 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.

  7. Cosmological Params (May 05) • Degeneracy breaking crucial • Combining CMB + SDSS + HST + SNIa Posterior probability

  8. Inflationary paradigm Flatness tot = 1.02 § 0.02 Bayesian evidence 18 : 1 Non-Gaussianity -58 <fnl < 134 inflation » 10-5 curvaton » 1 Planck (2007) > 5 isocurvature < 33% Bayesian evidence > 1000 : 1 in favor of adiabatic pert’ons Non-adiabaticity ns= 0.95 § 0.03 Planck (2007): 90% chance of disproving scale invariance with high evidence Scale invariance Gravity waves ? r10 < 0.35 Einf < 10-5 Mpl B-polarization smoking gun ! Direct detection: LIGO, Virgo, LISA

  9. The hidden assumptions RT, Riazuelo & Durrer (2001) RT & Durrer (2004) Beltran et al (2004) BBN b» 0.022 HST 0.72§0.08 Assumptions about initial fluctuations crucial for precision cosmology Polarization saves the day Pre-WMAP (2001), but still qualitatively the case Precision cosmology: <2% error on most parameters

  10. Exploring the cosmic neutrino background

  11. What good is cosmology? log r rrad ~ a - 4 time rmat ~ a - 3 rL = const log a radiation dominated matter dominated lambda dominated 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

  12. Massless families Matter/radiation equality affected • WMAP+ : 2.4 < N < 6.8 (2) • BBN :2.8 < N < 3.2 • CERN, 1991: N = 2.994 § 0.012

  13. Neutrino masses • Structure washed out below scales • knr» (m )1/2 (m h2 )1/2 While relativistic, neutrinos free-stream out of fluctuations Hu, Eisenstein & Tegmark 1998 • Mass hierarchy: • m122» 8 x 10-5 eV2 • m232» 2.6 x 10-3 eV2 • Absolute mass: • Tritium decay • m e < 2.3 eV (95% cl) • Cosmology : •  m < O(1) eV

  14. Detecting the CNB RT & Melchiorri 2004 Viscosity parameter cvis2: controls the free-streaming behaviour cvis2 = 1/3 : radiative viscosity free streaming cvis2 = 0 : perfect fluid no anisotropic stress (eg,   CDM coupling) acoustic oscillations Hu 1998

  15. Positive evidence for a CNB CMB alone CMB+SDSS CMB+SDSS CMB alone +BBN Assuming N = 3 • CMB + SLOAN • cvis2 = 0 clearly disfavored (about 2 ) • Bayesian model comparison: cvis2 = 1/3 favored • with odds 2:1 RT & Melchiorri 2004

  16. Automatic Occam’s razor w w0 CNB • Model comparison tools to assess the need for new parameters Mismatch with prediction ns : scale invariance  : flatness fiso : adiabaticity RT 2005

  17. 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

  18. 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

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