Boson Stars in Rastall Gravity

Boson stars equilibrium configurations in the framework of Rastall gravity are investigated. Rastall gravity theory is a phenomenological modification of General Relativity in which the usual covariant conservation of the stress–energy tensor is relaxed through a non-minimal coupling between matter and geometry. The gravitational field equations can be written in an Einstein-like form with an effective stress–energy tensor that depends explicitly on the trace of matter. The modified Tolman–Oppenheimer–Volkoff equations governing static, spherically symmetric configurations are derived and applied to model self-gravitating scalar matter described by a λϕ4 self-interaction potential. The corresponding fluid representation provides an effective equation of state used to construct the stellar models. The resulting mass–radius relations show that boson stars in Rastall gravity retain the qualitative structure known from General Relativity, including the existence of a maximum mass separating stable and unstable branches. However, quantitative deviations arise as the Rastall parameter increases. In particular, the critical mass decreases and the stellar radius becomes sensitive to the strength of the matter-geometry coupling.