Galilean Creation of the Inflationary Universe

TL;DR

This paper explores a novel inflationary scenario starting from Minkowski space using Galilean Genesis, which avoids initial singularities and is embedded in a broad class of stable scalar-tensor theories.

Contribution

It introduces a generic Lagrangian framework for the Genesis-to-inflation transition within a wider scalar-tensor theory class, avoiding instabilities and extending previous effective field theory approaches.

Findings

Stable primordial perturbations can be generated in the Genesis-inflation scenario.

The proposed model avoids Ostrogradski instabilities.

The scenario provides a non-singular beginning to inflation.

Abstract

It has been pointed out that the null energy condition can be violated stably in some non-canonical scalar-field theories. This allows us to consider the Galilean Genesis scenario in which the universe starts expanding from Minkowski spacetime and hence is free from the initial singularity. We use this scenario to study the early-time completion of inflation, pushing forward the recent idea of Pirtskhalava et al. We present a generic form of the Lagrangian governing the background and perturbation dynamics in the Genesis phase, the subsequent inflationary phase, and the graceful exit from inflation, as opposed to employing the effective field theory approach. Our Lagrangian belongs to a more general class of scalar-tensor theories than the Horndeski theory and Gleyzes-Langlois-Piazza-Vernizzi generalization, but still has the same number of the propagating degrees of freedom, and thus can avoid Ostrogradski instabilities. We investigate the generation and evolution of primordial perturbations in this scenario and show that one can indeed construct a stable model of inflation preceded by (generalized) Galilean Genesis.