Dynamical Dark Energy in Minimally Modified Gravity

TL;DR

This paper investigates minimally modified gravity models that include dynamical dark energy, analyzing linear perturbations to understand their effects on gravitational constants and sound speed, with implications for cosmological observations.

Contribution

It introduces a framework for minimally modified gravity with auxiliary constraints that sustain a dynamical cosmological background and explores their perturbative properties.

Findings

Modified effective gravitational constant

Non-zero sound speed for dust

Insensitivity of results to constraint details

Abstract

Minimally modified gravity is a class of models with only the two tensor degrees of freedom as in general relativity. Using the framework with auxiliary constraints these models can maintain a dynamical cosmological background. The form of the constraints is thereby restricted by the requirement of dynamical dark energy and the avoidance of a breakdown of perturbation theory. Studying the linear perturbations around the FLRW background the results are, however, quite insensitive to the details of the constraints leading to a modified effective gravitational constant or a non-vanishing sound speed for dust.