COSMOLOGYCOSMOLOGY

AS A TOOL AS A TOOL

FOR PARTICLE PHYSICSFOR PARTICLE PHYSICS

Roberto Trotta

University of Oxford

Astrophysics

&

Royal Astronomical Society

Vol. 302, 12/2003

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

OutlineOutline

Towards precision cosmology

Neutrino properties from high quality

cosmological observations

Conclusions & Outlook

Cosmological observablesCosmological observables

10-32 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 The Cosmic Microwave BackgroundBackground

Temperature fluctuation on the 2-sphere:

2-point correlation function:

Temperature power spectrum

Cosmology with the CMBCosmology 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)Cosmological Params (May 05)

Degeneracy breaking crucial

Combining CMB + SDSS + HST + SNIa

Post

eri

or

pro

babili

ty

Inflationary paradigmInflationary paradigm

B-polarization smoking gun !

Direct detection: LIGO, Virgo, LISA

Flatness tot = 1.02 § 0.02Bayesian evidence 18 : 1

Non-Gaussianity -58 < fnl < 134inflation » 10-5

curvaton » 1Planck (2007) > 5

Non-adiabaticity isocurvature < 33%Bayesian evidence > 1000 : 1in favor of adiabatic pert’ons

Scale invariance ns = 0.95 § 0.03Planck (2007): 90% chance of disprovingscale invariance with high evidence

Gravity waves ? r10 < 0.35Einf < 10-5 Mpl

The hidden assumptionsThe hidden assumptions

BBN b » 0.022

HST0.72§0.08

Assumptions about initial fluctuationscrucial 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?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

radiationdominated

matterdominated

lambdadominated

Massless familiesMassless families

CERN, 1991: N = 2.994 § 0.012

WMAP+ : 2.4 < N < 6.8 (2) BBN : 2.8 < N < 3.2

Matter/radiation equality affected

Neutrino massesNeutrino masses

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

Structure washed out below scales knr » (m )1/2 (m h2 )1/2

While relativistic, neutrinosfree-stream out of fluctuations

Hu, Eisenstein & Tegmark 1998

Detecting the CNBDetecting the CNB

cvis2 = 1/3 : radiative viscosity

free streaming

cvis2 = 0 : perfect fluid

no anisotropic stress (eg, CDM coupling)

acoustic oscillations

Viscosity parameter cvis2: controls the free-streaming behaviour

Hu 1998

RT & Melchiorri 2004

Positive evidence for a CNBPositive evidence for a CNB

CMB + SLOAN

cvis2 = 0 clearly disfavored (about 2

Bayesian model comparison: cvis2 = 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 razorAutomatic Occam’s razor

CNB

RT 2005

Model comparison tools to assess the need for new parameters

0

Mis

matc

h w

ith

pre

dic

tion

ns : scale invariance

: flatness

fiso : adiabaticity

Prospects for precision Prospects for precision cosmologycosmology

Temperature alone

Polarization alone

Almost orthogonal degeneracies

Polarization lifts flat directions in Temperature

Constraints improve significantly

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 OutlookConclusions and Outlook

Cosmology is a data-driven fielddata-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/matterdark energy/matter, brane--worlds, cosmic strings, topology,

axis of evil (?)

Watch out for:correlations between observations, high quality polarization data, high quality polarization data,

lensing, lensing, GW