Maximum mass limit of strange stars in quadratic curvature-matter coupled gravity
Debadri Bhattacharjee, Pradip Kumar Chattopadhyay, Kazuharu Bamba
TL;DR
The paper investigates the maximum mass of strange stars within a gravity theory that combines quadratic curvature and gravity–matter coupling, defined by $f(\tilde{R},T)=R+\alpha R^{2}+2\beta T$. It derives modified Tolman–Oppenheimer–Volkoff equations and solves them with the MIT bag equation of state to obtain mass–radius relations, revealing that $M_{\max}$ can reach up to about $3.11\,M_\odot$ for certain parameter choices, potentially explaining GW190814's lighter companion as a strange star. Stability analyses using the adiabatic index and Harrison–Zel’dovich–Novikov criteria indicate robust configurations within sizeable regions of $(\alpha,\beta,B_g)$, and the work outlines multi-messenger observational tests (GW, NICER, X-ray timing) to constrain the model. Overall, the extended gravity framework broadens the viable range of strange-star configurations and provides a pathway to test gravity–matter coupling with upcoming observations.
Abstract
We explore the maximum mass limit of strange stars in quadratic curvature gravity with the non-minimal matter coupling. The characteristic parameters of the quadratic curvature coupling and the non-minimal matter coupling imply the contributions from higher-order curvature terms and the coupling between matter and geometry, respectively. We explicitly demonstrate that the conservation of the energy-momentum tensor can be modified, and that in the vanishing limit of the non-minimal matter coupling, the formalism of general relativity is recovered. By deriving the Tolman-Oppenheimer-Volkoff equations from the gravitational field equations and applying the MIT bag model equation of state, we obtain the corresponding mass-radius relationships for strange stars. Furthermore, we show that the maximum mass limit of strange stars can exceed the general relativistic counterpart. Specifically, we find that a maximum mass up to 3.11 solar mass is achievable, suggesting that the lighter companion of GW190814 could plausibly be a strange star.