Cosmological Parameters and the WMAP data Antony Lewis CfA, Harvard / CITA, Toronto http://cosmologist.info • Standard assumptions – what are the parameters? • Unexpected features, validity of assumptions? • Low quadrupole, cut-off/running/dark energy • Asymmetries • ‘features’ of WMAP analysis
Cosmological Parameters and the WMAP data. Antony Lewis CfA, Harvard / CITA, Toronto http://cosmologist.info. Standard assumptions – what are the parameters? Unexpected features, validity of assumptions? Low quadrupole, cut-off/running/dark energy Asymmetries - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Cosmological Parameters and the WMAP data
Antony LewisCfA, Harvard / CITA, Toronto
http://cosmologist.info
• Standard assumptions – what are the parameters?
• Unexpected features, validity of assumptions?
• Low quadrupole, cut-off/running/dark energy• Asymmetries• ‘features’ of WMAP analysis
MCMC sampling for parameter estimation
• MCMC sample points in cosmological parameter space drawn from the posterior distribution given the data P(parameters|data)
• Each sample gives an equally likely set of parameters given the data. “possible universes”
• Number density of samples proportional to probability density
• Just requires a function to compute likelihood for each set of parameters
• CosmoMC code at http://cosmologist.info/cosmomc uses CAMB (http://camb.info) to generate Cl
l <~31 shows unlikely asymmetry:evaluate binned Cl on half sky as a function of axis: the lowest ratio of power on opposite two halves is small compared to simulations. Low power in N ecliptic hemisphere.
• Also astro-ph/0307282 find quadrupole and octopole alignment is unlikely at 1/60 level