From Big Bang Nucleosynthesis to Late-Time Acceleration in $f(Q,L_m)$ Gravity

TL;DR

This paper investigates an $f(Q,L_m)$ gravity model that unifies early and late cosmic evolution, constrained by diverse observational data and BBN, showing it can mimic $ ext{ extLambda}$CDM while allowing deviations.

Contribution

It introduces and tests a non-minimal coupling $f(Q,L_m)$ gravity model against observational data, establishing its viability as an alternative to $ ext{ extLambda}$CDM.

Findings

The model fits observational data well, including BAO, CC, and GW measurements.

Incorporating BBN constraints tightly bounds model parameters.

The model describes the transition from deceleration to acceleration successfully.

Abstract

We perform a comprehensive investigation of the early-to-late time cosmic evolution within the framework of $f(Q,L_m)$ gravity, characterized by a non-minimal coupling between non-metricity and matter. The model is further tested against a combined set of observational data, including DESI DR2 BAO, previous BAO measurements, cosmic chronometers (CC), and gravitational-wave (GW) standard sirens, using a Markov Chain Monte Carlo (MCMC) approach. Further by incorporating the Big Bang Nucleosynthesis (BBN) freeze-out constraint, we place stringent limits on the model parameters, ensuring consistency with early-Universe physics. The resulting constraints exhibit strong agreement with observations, with the model successfully describing the transition from decelerated to accelerated expansion. The evolution of the effective equation-of-state parameter, together with statefinder diagnostics and energy conditions, reveals a quintessence-like nature and confirms the physical viability of the model. Overall, the $f(Q,L_m)$ framework emerges as a viable alternative to $\Lambda$CDM, closely reproducing its predictions while allowing controlled deviations in the expansion history.