Initial conditions for inflation

TL;DR

This paper proposes a novel mechanism within the $oldsymbol{ extit{ ext{α}}}$-attractors framework that uses a proto-inflation phase to set initial conditions for plateau inflation, avoiding fine-tuning and sub-Planckian issues.

Contribution

It introduces a new approach where proto-inflation at the Planck scale prepares initial conditions for subsequent plateau inflation, overcoming previous initial conditions problems.

Findings

Proto-inflation can start at the Planck scale and set initial conditions for inflation.

Power-law proto-inflation avoids sub-Planckian eternal inflation.

A simple $oldsymbol{ extit{ ext{α}}}$-attractors model realizes the mechanism.

Abstract

Within the $\alpha$-attractors framework we investigate scalar potentials with the same pole as the one featured in the kinetic term. We show that, in field space, this leads to directions without a plateau. Using this, we present a proposal, which manages to overcome the initial conditions problem of inflation with a plateau. An earlier period of proto-inflation, beginning at Planck scale, accounts for the Universe expansion and arranges the required initial conditions for inflation on the plateau to commence. We show that, if proto-inflation is power-law, it does not suffer from a sub-Planckian eternal inflationary stage, which would otherwise be a problem. A simple model realisation is constructed in the context of $\alpha$-attractors, which can both generate the inflationary plateau and the exponential slopes around it, necessary for the two inflation stages. Our mechanism allows to assume chaotic initial conditions at the Planck scale for proto-inflation, it is generic and it is shown to work without fine-tuning.