Cosmology in scalar-vector-tensor theories

TL;DR

This paper explores scalar-vector-tensor theories in cosmology, deriving stability conditions for perturbations, analyzing primordial gravitational waves, and constructing a model where vector and scalar fields drive cosmic acceleration.

Contribution

It provides the first comprehensive stability analysis for scalar-vector-tensor theories with broken gauge symmetry and constructs a viable inflationary model with vector and scalar field interactions.

Findings

Derived conditions for ghost and Laplacian stability in these theories.

Calculated the primordial tensor power spectrum during inflation.

Presented a concrete inflationary model with stable vector and scalar field dynamics.

Abstract

We study the cosmology on the Friedmann-Lemaitre-Robertson-Walker background in scalar-vector-tensor theories with a broken $U(1)$ gauge symmetry. For parity-invariant interactions arising in scalar-vector-tensor theories with second-order equations of motion, we derive conditions for the absence of ghosts and Laplacian instabilities associated with tensor, vector, and scalar perturbations at linear order. This general result is applied to the computation of the primordial tensor power spectrum generated during inflation as well as to the speed of gravity relevant to dark energy. We also construct a concrete inflationary model in which a temporal vector component $A_0$ contributes to the dynamics of cosmic acceleration besides a scalar field $\phi$ through their kinetic mixings. In this model, we show that all the stability conditions of perturbations can be consistently satisfied during inflation and subsequent reheating.