New Old Inflation

TL;DR

New Old Inflation introduces a two-field, bubble-based inflationary scenario that abandons slow-roll in favor of locked inflation inside a nucleated bubble. Density perturbations arise from moduli-dependent decay rates rather than inflaton fluctuations, enabling a very low inflation scale and predicting negligible gravitational waves along with potentially zero tilt and enhanced non-Gaussianity. The framework naturally accommodates cascades of inflation, large initial Hubble via spurions, and a resolution to the cosmological moduli problem. Together, these features offer a distinctive alternative to conventional slow-roll models with potentially testable signatures in the scalar spectrum and non-Gaussianity.

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.