Cosmology of Extended Proca-Nuevo

TL;DR

This paper extends the Proca-Nuevo theory of a massive vector field by adding operators from the Generalized Proca class, maintaining consistency and stability, and explores its cosmological implications including self-accelerating solutions.

Contribution

It introduces an extension of Proca-Nuevo with Generalized Proca operators that preserves the primary constraint and explores its cosmological applications.

Findings

The extended theory maintains the primary constraint on flat and curved backgrounds.

It admits ghost-free, stable cosmological solutions with late-time acceleration.

Gravitational waves behave as in General Relativity in the solutions studied.

Abstract

Proca-Nuevo is a non-linear theory of a massive spin-1 field which enjoys a non-linearly realized constraint that distinguishes it among other generalized vector models. We show that the theory may be extended by the addition of operators of the Generalized Proca class without spoiling the primary constraint that is necessary for consistency, allowing to interpolate between Generalized Proca operators and Proca-Nuevo ones. The constraint is maintained on flat spacetime and on any fixed curved background. Upon mixing extended Proca-Nuevo dynamically with gravity, we show that the constraint gets broken in a Planck scale suppressed way. We further prove that the theory may be covariantized in models that allow for consistent and ghost-free cosmological solutions. We study the models in the presence of perfect fluid matter, and show that they describe the correct number of dynamical variables and derive their dispersion relations and stability criteria. We also exhibit, in a specific set-up, explicit hot Big Bang solutions featuring a late-time self-accelerating epoch, and which are such that all the stability and subluminality conditions are satisfied and where gravitational waves behave precisely as in General Relativity.