Primordial perturbations and precision cosmology from the Cosmic Microwave Background

Antony LewisCITA, University of Toronto

http://cosmologist.info

Hu & White, Sci. Am., 290 44 (2004)

Evolution of the universe

Opaque

Transparent

Perturbation evolutionEarly universe to last scattering

Contributions to cosmology

• Constraints on primordial perturbations• Observable primordial isocurvature and vector modes (identification and

predictions)• CMB polarization analysis: solution to E/B mode separation problem• Simulation and parameter estimation with CMB lensing

• Ab initio quantum gravity calculation of primordial perturbations and CMB in closed instanton model

• Fastest and most accurate code for calculating CMB anisotropy power spectra from initial conditions + parameters (CAMB)

• Methods for fast Monte Carlo parameter estimation from cosmological data (CosmoMC code)

• Accurate parameter constraints from CMB + other data (e.g. galaxy lensing) • Evolution of dark matter and dark energy perturbations: efficient methods,

numerical predictions, parameter constraints• CMB signatures of primordial magnetic fields

Redhead et al: astro-ph/0402359

CMB temperature power spectrumPrimordial perturbations + later physics

Primordial Perturbations

fluid at redshift < 109

• Photons

• Neutrinos

• Baryons + electrons

• Cold Dark Matter

• Dark energyprobably negligible early on

General regular perturbation

Scalar

Vector

Tensor

Adiabatic(observed)

Matter density

Cancelling matter density(unobservable)

Neutrino vorticity(very contrived)

Gravitational waves

Neutrino density(contrived)

Neutrino velocity(very contrived)

+ irregular modes, neutrino n-pole modes, n-Tensor modes Rebhan and Schwarz: gr-qc/9403032+ other possible components, e.g. defects, magnetic fields, exotic stuff…

General regular linear primordial perturbation

-iso

curv

atu

re-

Bridle, Lewis, Weller, Efstathiou: astro-ph/0302306

Adiabatic modesWhat is the primordial

power spectrum?

Isocurvature modesCurvaton model?

Gordon, Lewis: astro-ph/0212248

Primordial Gravitational Waves(tensor modes)

• Well motivated by some inflationary models- Amplitude measures inflaton potential at horizon crossing- distinguish models of inflation

• Observation would rule out other models - ekpyrotic scenario predicts exponentially small amplitude - small also in many models of inflation, esp. two field e.g. curvaton

• Weakly constrained from CMB temperature anisotropy

Look at CMB polarization

E and B polarization

• E polarization from scalar, vector and tensor modes

• B polarization only from vector and tensor modes

B is ‘smoking gun’ for primordial vector and tensor modes

Vector and Tensor B mode spectrum

Lewis: astro-ph/0403583

B-modes

Non-linear scalar modes also give small B signal

Polarization complications

• E/B mixing

• Lensing of the CMB

Underlying B-modes Part-sky mix with scalar E

Recovered B modes‘map of gravity waves’

Separation method

Observation

Lewis: astro-ph/0305545

E/B mixing and solution

Weak lensing of the CMB

Last scattering surface

Inhomogeneous universe - photons deflected

Observer

• Lensing B-modes• Changed power spectra

Lewis: PRD submitted; Challinor, Lewis: in preparation

Future work• Cosmological parameters from forthcoming CMB data (Planck,

Clover, etc.) + galaxy lensing etc.

• Reconstruction of initial power spectrum and constraints on inflation and other models

• Improved treatment of CMB lensing: lensing reconstruction, B-mode cleaning, un-lensing the temperature

• Statistical methods: Monte Carlo methods for CMB map-making, polarization analysis and weak lensing

• Cosmology from 21cm and galaxy weak lensing (+CMB)

• Tests of new physics, string theory, etc; early universe models

• New things…

CMB data alonecolor = optical depth

Samples in6D parameterspace

Parameter estimation: sampling from P(parameters|data)

e.g. CMB+galaxy lensing +BBN prior

Plot number density of samples as function of parameters

CosmoMC code at http://cosmologist.info/cosmomc Lewis, Bridle: astro-ph/0205436Contaldi, Hoekstra, Lewis: astro-ph/0302435

Conclusions• CMB contains lots of useful information!

- primordial perturbations + well understood physics (cosmological parameters)

• Precision cosmology- sampling methods used to constrain many parameters with full posterior distribution

• Currently no evidence for any deviations from standard near scale-invariant purely adiabatic primordial spectrum

• B-mode polarization - primordial gravitational waves + vector modes: - energy scale of inflation - rule out most ekpyrotic and pure curvaton/ inhomogeneous reheating models and others

• Weak lensing of CMB :- B-modes potentially confuse primordial signals- Have to account for effect on power spectra

• Foregrounds, systematics, etc, may make things much more complicated!