A Study of Structure Formation and Reheating in the D3/D7 Brane Inflation Model

TL;DR

This paper analyzes the spectrum of fluctuations in the D3/D7 brane inflation model, focusing on the rapid reheating process driven by tachyonic instability and parametric resonance, and its impact on cosmological curvature fluctuations.

Contribution

It provides an analytical study of the reheating dynamics in the D3/D7 brane inflation model, highlighting the role of tachyonic instability and parametric resonance in energy transfer.

Findings

Rapid energy transfer via tachyonic instability during preheating.

Efficient conversion of background field energy into matter fluctuations.

Potential large-scale curvature fluctuations from entropy mode growth.

Abstract

We study the spectrum of cosmological fluctuations in the D3/D7 brane inflationary universe with particular attention to the parametric excitation of entropy modes during the reheating stage. The same tachyonic instability which renders reheating in this model very rapid leads to an exponential growth of entropy fluctuations during the preheating stage which in turn may induce a large contribution to the large-scale curvature fluctuations. We take into account the effects of long wavelength quantum fluctuations in the matter fields. As part of this work, we perform an analytical analysis of the reheating process. We find that the initial stage of preheating proceeds by the tachyonic instability channel. An upper bound on the time it takes for the energy initially stored in the inflaton field to convert into fluctuations is obtained by neglecting the local fluctuations produced during the period of tachyonic decay and analyzing the decay of the residual homogeneous field oscillations, which proceeds by parametric resonance. We show that in spite of the fact that the resonance is of narrow-band type, it is sufficiently efficient to rapidly convert most of the energy of the background fields into matter fluctuations.