Dark energy and a new realization of the matter Lagrangian

TL;DR

This paper introduces a novel matter Lagrangian modeling dark energy as a thermodynamic combination, demonstrating its independence from existing models and analyzing its cosmological implications through observational data.

Contribution

It presents a new matter Lagrangian formulation for dark energy that is independent of matter-geometry couplings and explores its cosmological effects and observational constraints.

Findings

The new Lagrangian allows separate conservation of baryonic matter and dark energy.

Different choices of matter Lagrangian in $\\Lambda$CDM are not equivalent.

The model with logarithmic dark energy fits observational data and predicts late-time universe behavior.

Abstract

A new realization of the matter Lagrangian is introduced which models the dark energy component as a non-standard combination of thermodynamics quantities of the baryonic matter. We will prove that the present realization is independent of existing models with matter-geometry couplings and has a property that the energy-momentum tensor of both baryonic matter and dark energy is conserved separately. We further show that two possible choices of the matter Lagrangian in the $\Lambda$CDM model are not totally equivalent and investigate the background and perturbative constraints on the form of matter Lagrangian. We will also investigate cosmological implications of a test model with logarithmic DE and obtain the model parameters by confronting the model with observational data on the cosmic chronometers, Pantheon$^+$ and $f\sigma_8$ datasets. We will also explain in details the predictions of the model on the late time behavior of the universe and compare the result with $\Lambda$CDM model.