White dwarf stars in Randall–Sundrum II braneworld gravity: perturbative bounds on super-chandrasekhar configurations

Abstract We investigate the equilibrium structure of white dwarf stars in the Randall–Sundrum II braneworld scenario using the effective brane-TOV formulation, with the stellar matter described by the zero-temperature Chandrasekhar electron-degenerate equation of state at mean molecular weight per electron $$\mu _e = 2$$ μ e = 2 . Scanning a range of brane tensions and Weyl-fluid closure parameters, we ask whether the braneworld corrections can support the super-Chandrasekhar masses ( $$\sim 2\,M_\odot $$ ∼ 2 M ⊙ ) inferred for some over-luminous Type Ia supernova progenitors. To distinguish brane effects within the perturbative regime from formal extrapolations of the effective four-dimensional equations, we introduce a local, mass-based perturbativity diagnostic that compares the solution including the full Weyl evolution with the quadratic-correction-only solution at the same brane tension and central density. We do not compare against an independent non-perturbative five-dimensional solution – none currently exists in the literature for this configuration – but instead assess the perturbative admissibility of the solutions obtained after adopting the CAM closure. The general-relativistic limit is recovered with a Chandrasekhar mass of $$1.425\,M_\odot $$ 1.425 M ⊙ , and within the perturbative-validity regime the maximum white dwarf mass is $$\simeq 1.50\,M_\odot $$ ≃ 1.50 M ⊙ – about $$5\%$$ 5 % above this value and well below $$2\,M_\odot $$ 2 M ⊙ . Masses approaching $$2\,M_\odot $$ 2 M ⊙ arise only where the Weyl contribution is no longer perturbative. We conclude that, within the CAM-closed effective brane formulation and subject to the perturbative-validity criterion adopted here, RS-II braneworld corrections can mildly raise the Chandrasekhar mass scale but do not robustly support physical super-Chandrasekhar white dwarfs.