New DBI Inflation model with Kinetic Coupling to Einstein Gravity

TL;DR

This paper introduces a new class of inflation models called the 'new DBI inflation model' that incorporates a nonminimal kinetic coupling to Einstein gravity, potentially affecting inflationary spectra without adding new degrees of freedom.

Contribution

The paper proposes a novel inflation model extending DBI action with a nonminimal kinetic coupling, maintaining second-order equations and exploring observable effects on spectra.

Findings

The model remains second-order in equations of motion.

It introduces a $k^4$ correction in perturbations.

Potential observable effects on inflationary spectra.

Abstract

In this paper we study a new class of inflation models which generalize the Dirac-Born-Infeld (DBI) action with the addition of a nonminimal kinetic coupling (NKC) term. We dubbed this model as the {\it new DBI inflation model}. The NKC term does not bring new dynamical degree of freedom, so the equations of motion remain of second order. However, with such a coupling, the action is no longer linear with respect to the Einstein curvature term ($R$ or $G^{\mu\nu}$), which leads to a correction term of $k^4$ in the perturbations. The new DBI inflation model can be viewed as theories beyond Horndeski. Without violating nearly scale-invariance, such a correction may lead to new effects on the inflationary spectra that could be tested by future observations.