Effect of initial condition of inflation on power and angular power spectra in finite slow-roll inflation

TL;DR

This paper investigates how initial conditions of inflation influence the scalar and tensor power spectra, revealing oscillations and step-like features that can explain certain CMB observations, with implications for inflation models.

Contribution

It introduces a generalized initial state in inflation, showing how finite inflation length and pre-inflation conditions affect observable power spectra and their fit to WMAP3 data.

Findings

Power spectrum exhibits step-like variation with inflation length.

Oscillations in the power spectrum depend on pre-inflation conditions.

Small-field inflation with scalar matter pre-inflation best fits WMAP3 data.

Abstract

The effect of the initial condition of inflation on the power spectra of scalar and tensor perturbations is estimated assuming a slow-roll inflation model. By defining a more general initial state in inflation particular properties of the power spectrum such as oscillation can be revealed. The behavior of the power spectrum is shown to exhibit a step-like variation with respect to finite inflation length in cases of both radiation- and scalar matter-dominated pre-inflation. The power spectrum is shown to oscillate in the radiation-dominated case. The effects of such a power spectrum on the TT and TE power spectra are examined for three typical slow-roll inflation models; a small-field model, a large field model, and a hybrid model, considering both pre-inflation models. It is found that the discrepancies between WMAP3 data and the Lambda CDM model, such as suppression of the spectrum at l=2, may be explained to a certain extent by the finite length of inflation for inflation of close to 60 e-folds. The small-field inflation model with scalar matter-dominated pre-inflation provides the best fit to the WMAP3 data among the models considered. Relatively large changes in the angular TT power spectrum occur in response to small changes in inflation length in the radiation-dominated pre-inflation models, and half cases do not fit well with the observed data. This behavior is considered to be attributable to the oscillatory behavior of the power spectrum. The scalar matter-dominated case is thus preferred to the radiation-dominated case of pre-inflation, independent of the length of inflation.