New Old Inflation

TL;DR

This paper introduces a novel inflationary model based on modified old inflation, involving a tunneling event and a secondary inflationary phase within a bubble, predicting unique observational signatures.

Contribution

It presents a new class of inflationary solutions that do not rely on slow-roll potentials and naturally address the cosmological moduli problem.

Findings

Predicts negligible gravity waves

Possible absence of scalar tilt

Higher non-Gaussianity than other models

Abstract

We propose a new class of inflationary solutions to the standard cosmological problems (horizon, flatness, monopole,...), based on a modification of old inflation. These models do not require a potential which satisfies the normal inflationary slow-roll conditions. Our universe arises from a single tunneling event as the inflaton leaves the false vacuum. Subsequent dynamics (arising from either the oscillations of the inflaton field or thermal effects) keep a second field trapped in a false minimum, resulting in an evanescent period of inflation (with roughly 50 e-foldings) inside the bubble. This easily allows the bubble to grow sufficiently large to contain our present horizon volume. Reheating is accomplished when the inflaton driving the last stage of inflation rolls down to the true vacuum, and adiabatic density perturbations arise from moduli-dependent Yukawa couplings of the inflaton to matter fields. Our scenario has several robust predictions, including virtual absence of gravity waves, a possible absence of tilt in scalar perturbations, and a higher degree of non-Gaussianity than other models. It also naturally incorporates a solution to the cosmological moduli problem.