A graceful entrance to braneworld inflation

TL;DR

This paper explores how oscillatory, positively-curved universes in braneworld models can naturally transition into inflation, highlighting conditions under which a scalar field climbs its potential during cycles before inflation begins.

Contribution

It demonstrates that certain braneworld models can facilitate a graceful entrance to inflation through oscillatory pre-inflationary dynamics, expanding understanding of early universe scenarios.

Findings

Oscillatory universes can enable scalar fields to climb potentials during cycles.

Conditions for a graceful entrance are derived for braneworld models.

The Shtanov-Sahni model can realize a graceful entrance in a wide parameter space.

Abstract

Positively-curved, oscillatory universes have recently been shown to have important consequences for the pre-inflationary dynamics of the early universe. In particular, they may allow a self-interacting scalar field to climb up its potential during a very large number of these cycles. The cycles are naturally broken when the potential reaches a critical value and the universe begins to inflate, thereby providing a `graceful entrance' to early universe inflation. We study the dynamics of this behaviour within the context of braneworld scenarios which exhibit a bounce from a collapsing phase to an expanding one. The dynamics can be understood by studying a general class of braneworld models that are sourced by a scalar field with a constant potential. Within this context, we determine the conditions a given model must satisfy for a graceful entrance to be possible in principle. We consider the bouncing braneworld model proposed by Shtanov and Sahni and show that it exhibits the features needed to realise a graceful entrance to inflation for a wide region of parameter space.