Effects of the matter Lagrangian degeneracy in $f(Q,T)$ gravity

TL;DR

This paper explores how the choice of matter Lagrangian in $f(Q,T)$ gravity affects cosmological models, revealing that different Lagrangian forms lead to significant variations in theoretical predictions and observational parameters.

Contribution

It demonstrates the impact of matter Lagrangian degeneracy on $f(Q,T)$ gravity's cosmological equations and parameter estimations, emphasizing the need to consider both forms in future studies.

Findings

Different matter Lagrangians alter density evolution of matter and radiation.

The form of the Lagrangian influences the generalized Friedmann equations.

Cosmological parameter confidence regions vary with Lagrangian choice.

Abstract

In this paper, we investigated the theoretical and cosmological effects of the matter Lagrangian degeneracy in an extension of the Symmetric Teleparallel Equivalent of General Relativity, denoted as $f (Q, T )$ gravity. This degeneracy comes from the fact that both $\mathcal{L}_m = p$ and $\mathcal{L}_m = -\rho$ can give rise to the stress-energy tensor of a perfect fluid. The $f(Q,T)$ equations depend on the form of the matter Lagrangian and hence they also have a degeneracy that has influence on the density evolution of dust matter and radiation, on the form of the generalized Friedmann equations and also shows changes in the cosmological parameters confidence regions when performing Monte Carlo Markov Chains analyses. Our results suggest that since changing the matter Lagrangian causes different theoretical and cosmological results, future studies in $f(Q,T)$ gravity should consider both forms of the matter Lagrangians to account for the different mathematical and observational results.