Effects of Axion Interactions on Quark Stars in 4D Einstein-Gauss-Bonnet Gravity

Abstract

We explore the properties of quark stars by combining the microscopic axion-extended Polyakov--Nambu--Jona-Lasinio model with the macroscopic framework of four-dimensional Einstein-Gauss-Bonnet (4D EGB) gravity. Our results show that the inclusion of axion-induced interactions stiffens the equation of state of quark matter, thereby increasing the sound speed and the maximum mass of quark stars. The inclusion of the 4D EGB correction effectively weakens gravitational compression and further modifies the stellar structure, allowing for larger radii and higher maximum masses while reducing the compactness and surface gravitational redshift. Notably, the combined effects yield mass-radius sequences that are more compatible with current observational constraints than those obtained under standard general relativity with conventional quark-matter equations of state. These findings suggest that the interplay between axion dynamics and 4D EGB gravity may provide a viable phenomenological framework for describing massive quark stars.