Multifield theories invariant under transverse diffeomorphisms: The mixed regime case

TL;DR

This paper investigates theories with broken diffeomorphism invariance down to transverse diffeomorphisms involving multiple scalar fields in cosmology, revealing energy exchange mechanisms and their implications for the dark sector.

Contribution

It introduces a covariantized framework for multifield TDiff theories with power-law couplings, analyzing their phenomenological effects on dark sector dynamics.

Findings

Energy exchange occurs between scalar fields due to non-conservation of individual energy-momentum tensors.

The covariantized approach allows a Diff-invariant description with an additional scalar field.

Potential implications for dark matter and dark energy phenomenology.

Abstract

We study theories breaking diffeomorphism (Diff) invariance down to the subgroup of transverse diffeomorphisms (TDiff), consisting of multiple scalar fields in a cosmological background. In particular, we focus on models involving a field dominated by its kinetic term and a field dominated by its potential, coupled to gravity through power-law functions of the metric determinant. The Diff symmetry breaking results in the individual energy-momentum tensors not being conserved, although the total conservation-law is satisfied. Consequently, an energy exchange takes place between the fields, acting as an effective interaction between them. With this in mind, we consider the covariantized approach to describe the theory in a Diff invariant way but with an additional field, and discuss the phenomenological consequences of these models when it comes to the study of the dark sector.