Inflation in a scalar-vector-tensor theory

TL;DR

This paper investigates inflation within a specific scalar-vector-tensor gravity model without U(1) symmetry, demonstrating its viability through analytical derivations and numerical analysis, and highlighting the role of coupling functions in achieving sufficient inflation.

Contribution

The study constructs a particular scalar-vector-tensor inflation model, derives its equations, and numerically verifies its viability, emphasizing the importance of coupling functions for successful inflation.

Findings

The model can produce sufficient e-foldings for inflation.

Coupling functions significantly enhance inflationary dynamics.

Stability conditions are satisfied during inflation.

Abstract

In this work, we study inflation in a particular scalar-vector-tensor theory of gravitation without the $U(1)$ gauge symmetry. The model is constructed from the more general action introduced in Heisenberg et al. (Phys Rev D 98:024038, 2018) using certain specific choices for the Lagrangians and the coupling functions. Also, for this model we build the explicit form for the action, and from it, we derive the general equations: the energy-momentum tensor and the equations of motion, and using the flat FLRW background, we have analyzed if it's possible to obtain an inflationary regime with it. Additionally, using particular choices for the potential, the coupling functions, suitable dimensionless coupling constants and initial conditions, it was possible verify numerically that this model of inflation is viable. In this sense, we could verify that the introduction of the coupling function $f(\phi)$ in our model of inflation, allows us to reach a suitable amount of $e$-foldings $N$ for sufficient inflation. This is a remarkable result, since without the coupling function contribution, the amount of $e$-foldings is smaller at the end of inflation, as has been demonstrated in Heisenberg et al. (2018). Also, the no-ghosts and stability conditions that the model during inflation must satisfy, i.e., absence of ghosts and Laplacian instabilities of linear cosmological perturbations were obtained, furthermore these conditions were verified numerically too.