White dwarf structure in f(R, T, Lm) gravity: Beyond the Chandrasekhar mass limit

In this work, we investigate the relativistic structure of white dwarfs (WDs) within the framework of modified gravity theory f ( R , T , L m ) = R + α T L m , which introduces a non-minimal coupling between matter and curvature. Using a realistic equation of state (EoS) that includes contributions from a relativistic degenerate electron gas and ionic lattice effects, we solve the modified Tolman-Oppenheimer-Volkoff (TOV) equations for two standard choices of the matter Lagrangian density: L m = p and L m = − ρ . We show that the extra αTL m term significantly alters the mass-radius relation of WDs, especially at high central densities ( ρ c ≳ 10 8 − 10 9 g / c m 3 ) , allowing for stable super-Chandrasekhar configurations. In particular, depending on the sign and magnitude of the parameter α , the maximum mass can increase or decrease, and in some regimes, the usual critical point indicating the transition from stability to instability disappears. Our findings suggest that f ( R, T, L m ) gravity provides a viable framework to explain the existence of massive WDs beyond the classical Chandrasekhar limit. Using Bayesian inference with WD observational data, we further constrain the coupling parameter α for the two choices of the Lagrangian density L m .

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