Reheating the Universe after String Theory Inflation

TL;DR

This paper investigates the reheating process after string theory inflation, analyzing energy transfer channels, cosmological constraints, and the resulting gravitational wave background, with implications for single and multiple throat scenarios.

Contribution

It provides a detailed analysis of reheating mechanisms in string inflation models, including energy decay channels and constraints from cosmological data, especially in multi-throat scenarios.

Findings

Reheating is viable in single throat or specific multiple throat models.

Graviton production is suppressed but leaves a residual gravitational wave background.

Overproduction of KK modes is a significant challenge in certain scenarios.

Abstract

In String theory realizations of inflation, the end point of inflation is often brane-anti brane annihilation. We consider the processes of reheating of the Standard Model universe after brane inflation. We identify the channels of inflaton energy decay, cascading from tachyon annihilation through massive closed string loops, KK modes, and brane displacement moduli to the lighter standard model particles. Cosmological data constrains scenarios by putting stringent limits on the fraction of reheating energy deposited in gravitons and nonstandard sector massive relics. We estimate the energy deposited into various light degrees of freedom in the open and closed string sectors, the timing of reheating, and the reheating temperature. Production of gravitons is significantly suppressed in warped inflation. However, we predict a residual gravitational radiation background at the level $\Omega_{GW} \sim 10^{-8}$ of the present cosmological energy density. We also extend our analysis to multiple throat scenarios. A viable reheating would be possible in a single throat or in a certain subclass of multiple throat scenarios of the KKLMMT type inflation model, but overproduction of massive KK modes poses a serious problem. The problem is quite severe if some inner manifold comes with approximate isometries (angular KK modes) or if there exists a throat of modest length other than the standard model throat, possibly associated with some hidden sector (low-lying KK modes).