Exponential Inflation With $\rho = +p$

TL;DR

This paper proposes a novel scalar field inflation model driven solely by quadratic kinetic energy with a negative sign, achieving exponential inflation without potentials or modified gravity, and discusses its physical implications and exit strategies.

Contribution

It introduces a new inflationary framework using a quadratic kinetic term with a wrong sign, avoiding the need for potentials or higher derivatives, and enabling exponential inflation.

Findings

Achieves exponential inflation driven by quadratic kinetic energy.

Does not require a potential or higher derivative actions.

Provides mechanisms for graceful exit from inflation.

Abstract

We introduce in this paper a new framework for obtaining a period of exponential inflation that is entirely driven by the quadratic kinetic energy of a scalar field. In contrast to recent attempts to realize scalar field inflation without potentials (such as k-inflation or ghost inflation), we find that it is possible to obtain exponential inflation, without invoking any higher derivative actions, or modifying gravity, and that unlike all previous approaches, we do not require a $\rho = -p$ phase in order to realize inflation. The inflaton in our proposed framework is a scalar field with a quadratic kinetic energy term, but with the `wrong sign'. We take the perspective that this is due to some temporary instability in our system at high energies, and provide physical examples of situations where a modulus field might temprorarily exhibit such behaviour. The deflation of extra dimensions is a neccesary feature of our framework. However, unlike in previous attempts at Kaluza-Klein inflation, it is possible to obtain exponential (as opposed to power law or pole) inflation. We provide several indications of how one can gracefully exit from this type of inflation.