A Lagrangian description of interacting dark energy

TL;DR

This paper introduces a covariant relativistic model of interacting dark energy where the cosmological constant varies with the trace of the energy-momentum tensor, offering a more general framework than existing $f(R)$ gravity theories.

Contribution

It develops a Lagrangian-based covariant model of dark energy interaction with a variable cosmological constant dependent on matter properties.

Findings

Cosmological data favor a variable cosmological constant.

The $ ext{Lambda}(T)$ gravity aligns with observational data.

The model generalizes Palatini $f(R)$ gravity by including matter pressure.

Abstract

We propose a relativistically covariant model of interacting dark energy based on the principle of least action. The cosmological term $\Lambda$ in the gravitational Lagrangian is a function of the trace of the energy--momentum tensor $T$. We find that the $\Lambda(T)$ gravity is more general than the Palatini $f(R)$ gravity, and reduces to the latter if we neglect the pressure of matter. We show that recent cosmological data favor a variable cosmological constant and are consistent with the $\Lambda(T)$ gravity, without knowing the specific function $\Lambda(T)$.