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!