Study of Curvature-Matter Coupling in Modified Gravity

TL;DR

This paper explores the $f(R, L_m)$ modified gravity framework, analyzing its implications for cosmic acceleration, bounce cosmologies, and baryogenesis, using observational data and theoretical models to address key cosmological challenges.

Contribution

It introduces and investigates the $f(R, L_m)$ gravity model, extending $f(R)$ theories with curvature-matter coupling, and applies it to various cosmological phenomena and observational datasets.

Findings

Demonstrates a deceleration-to-acceleration transition in specific $f(R, L_m)$ models.

Shows bulk viscosity can explain late-time acceleration within this framework.

Supports gravitational baryogenesis consistent with observed baryon-to-entropy ratio.

Abstract

Over the past century, General Relativity (GR) has been a cornerstone of gravitational theory. However, recent cosmological observations, such as the accelerated expansion of the Universe, challenge its completeness and the standard $\Lambda$CDM model. This has motivated the development of alternative approaches, including dynamical dark energy and modifications to gravity. This thesis investigates the $f(R, L_m)$ gravity framework, which extends $f(R)$ gravity by introducing curvature-matter coupling, to address unresolved issues in modern cosmology. Chapter 1 reviews the foundations of cosmology, GR, and $\Lambda$CDM, discussing their challenges and introducing modified gravity theories. Chapter 2 studies cosmic expansion in a specific non-linear $f(R, L_m)$ model, analyzing its dynamics using updated $H(z)$ and Pantheon datasets and demonstrating a deceleration-to-acceleration transition. Chapter 3 introduces a model-independent Hubble parameter parametrization and explores cosmological variables using MCMC and combined data. Chapter 4 incorporates bulk viscosity into $f(R, L_m)$ models to explain late-time acceleration and applies Om diagnostics and energy conditions. Chapter 5 examines non-singular matter bounce cosmologies, analyzing bouncing dynamics and the evolution of cosmographic parameters. Chapter 6 addresses gravitational baryogenesis and shows how $f(R, L_m)$ gravity supports the observed baryon-to-entropy ratio. Chapter 7 summarizes the results and suggests directions for future work.