Little Inflatons and Gauge Inflation

TL;DR

This work introduces little inflatons, a class of pseudo-Nambu-Goldstone inflatons protected by collective symmetry breaking, as natural slow-roll candidates for hybrid inflation in both non-supersymmetric and supersymmetric contexts; it develops concrete models, including a minimal littlest inflaton from an approximate $SO(2)$ symmetry and a supersymmetric realization that evades the supergravity $\eta$ problem via shift symmetry, as well as extra-dimensional constructions where the inflaton is the fifth component of a gauge field or a Wilson line. It extends the mechanism to higher dimensions, exploring a 5D gauge theory with a cosine-like potential, a 6D setup with a waterfall tied to higher-dimensional gauge components, and a deconstructed moose realization, highlighting how radiative and Coleman-Weinberg corrections can drive slow-roll with order-one parameters. The paper analyzes the impact of WMAP data, noting that supersymmetric models naturally predict a red tilt and a possible blue-to-red transition, while non-supersymmetric gauge inflation faces more constrained predictions; overall, the little inflaton framework offers a natural, technically natural approach to inflation with testable CMB signatures and connections to extra dimensions and radion dynamics.

Abstract

Cosmological inflation gives a natural answer for a variety of cosmological questions, including the horizon problem, the flatness problem, and others. However, inflation yields new questions relating to the flatness of the inflaton potential. Recent studies of ``little'' fields, a special class of pseudo-Goldstone bosons, have shown it is possible to protect the mass of a field while still yielding order one interactions with other fields. In this paper, we will show that ``little inflatons'' are natural candidates for the slow roll field of hybrid inflation models. We consider both supersymmetric and non-supersymmetric models, and give a simple examples based on approximate Abelian symmetries which solve the inflaton flatness problem of supergravity. We also present hybrid models in which components of gauge fields in higher dimensions play the role of the inflaton. Protected by higher-dimensional gauge symmetry, they, too, naturally have large couplings while suppressed mass terms. We summarize the implications of the new WMAP data on such models.