Anisotropic Inflation with Derivative Couplings

TL;DR

This paper investigates anisotropic inflation models with derivative couplings between the inflaton and a vector field, demonstrating stable solutions that reduce anisotropy and align with observational constraints.

Contribution

It introduces and analyzes anisotropic inflationary solutions with derivative couplings, extending previous models and showing their stability and observational viability.

Findings

Anisotropic solutions exist and are stable.

Derivative couplings reduce anisotropy levels.

Models remain consistent with current observational limits.

Abstract

We study anisotropic inflationary solutions when the inflaton and its derivative couple to a vector field. This type of coupling is motivated by D-brane inflationary models, in which the inflaton, and a vector field living on the D-brane, couple disformally (derivatively). We start by studying a phenomenological model where we show the existence of anisotropic solutions and demonstrate their stability via a dynamical system analysis. Compared to the case without a derivative coupling, the anisotropy is reduced and thus can be made consistent with current limits, while the value of the slow-roll parameter remains almost unchanged. We also discuss solutions for more general cases, including D-brane like couplings.