Energy transfer in multi field inflation and cosmological perturbations

Abstract

In cascade inflation and some other string inflation models,collisions of mobile branes with other branes or orbifold planesoccur and lead to interesting cosmological signatures. Thefundamental M/string-theory description of these collisions is stilllacking but it is clear that the inflaton looses part of its energyto some form of brane matter, e.g. a component of tensionlessstrings. In the absence of a fundamental description, we assume ageneral barotropic fluid on the brane, which absorbs part of theinflaton's energy. The fluid is modeled by a scalar with a suitableexponential potential to arrive at a full-fledged field theorymodel. We study numerically the impact of the energy transfer from theinflaton to the scalar on curvature and isocurvatureperturbations and demonstrate explicitly that the curvature powerspectrum gets modulated by oscillations which damp away towardsmaller scales. Even though, the contribution of isocurvatureperturbations decays toward the end of inflation, they inducecurvature perturbations on scales that exit the horizon before thecollision. We consider cases where the scalar behaves likeradiation, matter or a web of cosmic strings and discuss thedifferences in the resulting power spectra.