Energy Transfer in Multi Field Inflation and Cosmological Perturbations

TL;DR

This paper models energy transfer during multi-field inflation, analyzing how collisions and brane matter influence cosmological perturbations and the resulting power spectra.

Contribution

It introduces a scalar field model for brane matter with energy transfer effects, exploring their impact on curvature and isocurvature perturbations in inflation.

Findings

Curvature power spectrum exhibits oscillations dampening at smaller scales.

Isocurvature perturbations decay but influence earlier horizon exit scales.

Different brane matter behaviors (radiation, matter, strings) affect the power spectra.

Abstract

In cascade inflation and some other string inflation models, collisions of mobile branes with other branes or orbifold planes occur and lead to interesting cosmological signatures. The fundamental M/string-theory description of these collisions is still lacking but it is clear that the inflaton looses part of its energy to some form of brane matter, e.g. a component of tensionless strings. In the absence of a fundamental description, we assume a general barotropic fluid on the brane, which absorbs part of the inflaton's energy. The fluid is modeled by a scalar with a suitable exponential potential to arrive at a full-fledged field theory model. We study numerically the impact of the energy transfer from the inflaton to the scalar on curvature and isocurvature perturbations and demonstrate explicitly that the curvature power spectrum gets modulated by oscillations which damp away toward smaller scales. Even though, the contribution of isocurvature perturbations decays toward the end of inflation, they induce curvature perturbations on scales that exit the horizon before the collision. We consider cases where the scalar behaves like radiation, matter or a web of cosmic strings and discuss the differences in the resulting power spectra.