Brane inflation and the overshoot problem

Abstract

We investigate recent claims that brane inflation solves the overshoot problem through a combination of microphysical restrictions on the phase space of initial conditions and the existence of the Dirac-Born-Infeld attractor in regimes where the slow-roll attractor does not apply. Carrying out a comprehensive analysis of the parameter space allowed by the latest advances in brane inflation model-building, we find that these restrictions are insufficient to solve the overshoot problem. The vast majority of the phase space of initial conditions is still dominated by overshoot trajectories. We present an analytic proof that the brane-inflationary attractor must be close to the slow-roll limit, and update the predictions for observables such as non-Gaussianity, cosmic string tension and tensor modes. Contents

Inflation and String Theory

“…When the potential is approximately flat in a small fraction of the field space, and is steep elsewhere, then generic trajectories passing through the would-be inflationary region will overshoot the flat portion without initiating an inflationary phase, as emphasized long ago in [658]. The DBI kinetic term (see §5.3) has been argued to ameliorate the overshoot problem [659], though this conclusion was challenged by [660]. Negative spatial curvature resulting from tunneling entirely removes overshooting in certain classes of potential, and reduces its severity in general [661,662].…”

Full trispectrum in single field DBI inflation

“…In particular the DBI-inflation model [54], which is constructed within string theory, is such an example. For current and stringent observational constraints and consequences of DBI-inflation see [55,56,57,58,59,60,61,62,63].…”

Cosmological dynamics of a Dirac-Born-Infeld field

“…Furthermore, because of the dependence of the effective four dimensional string tension on the nature of the compact internal space, it is possible to place further constraints on the parameters related with compactifications such as flux numbers. For the most up to date observational constraints on and consequences of DBI inflation, see [35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Recently the idea of low scale inflation arising from the DBI action has been invoked to explain the late time acceleration we associate with dark energy [49][50][51][52].…”