Constraints on the primordial power spectrum from high-resolution Lyman α forest spectra and WMAP

Abstract

ABSTRACT The combined analysis of the cosmic microwave background on large scalesand Lyman-α forest on small scales provides a sufficiently long lever arm toobtain strong constraints on the slope and curvature of the power spectrumof primordial density fluctuations. We present results from the combination ofthe first year WMAP data and the dark matter power spectrum inferred byViel et al. (2004) for two different sets of high resolution and high signal-to-noise quasar absorption spectra: the Croft et al. (2002) sample with a medianredshift z = 2.72 and the LUQAS sample (Kim et al. 2004) with a medianredshift z = 2.125. The best fit value for the rms fluctuation amplitude ofmatter fluctuations is σ 8 = 0.94±0.08and n s = 0.99±0.03,if we do not includerunning of the spectral index. The best fit model with a running spectral indexhas parameters n s = 0.959±0.036and n run = −0.033±0.025.The data is thusconsistent with a scale-free primordial power spectrum with no running of thespectral index. We further include tensor modes and constrain the slow-rollparameters of inflation.Key words: Cosmology: observations – cosmology: theory - cosmic mi-crowave background – quasars: absorption lines