D. S. Pereira, S. Capozziello, F. S. N. Lobo, J. P. Mimoso
Abstract
Hybrid metric-Palatini gravity unifies the metric and Palatini formalisms while preserving a propagating scalar degree of freedom, offering a compelling route to modified gravity consistent with current observations. Motivated by this success, we consider an extended framework—the hybrid metric-Palatini scalar-tensor (HMPST) theory—in which an additional scalar field ϕ modulates the curvature couplings, enriching the dynamics and enabling nontrivial self-interactions through scalar potentials. We focus on the analytically tractable linear-f(R^) subclass and study its cosmological, strong-field, and weak-field regimes. In homogeneous and isotropic settings, we identify de Sitter and matter-dominated cosmological solutions describing accelerated expansion and early-Universe behavior. For static, spherically symmetric configurations, the field equations yield analytic solutions generalizing the Janis-Newman-Winicour and Buchdahl metrics, including the Schwarzschild─de Sitter limit. In the weak-field regime, linearized perturbations around Minkowski space lead to Yukawa-type corrections to the gravitational potential, with an effective Newton constant Geff and post-Newtonian parameter γ that recover general relativity for heavy or weakly coupled scalars. These results show that the linear-f(R^) HMPST subclass provides a consistent and unified description of gravity across cosmological, astrophysical, and Solar System scales, offering a fertile framework for connecting modified gravity to observations and effective field-theoretic extensions.
Keywords
GENERAL-RELATIVITY; DARK-MATTER; PULSAR; FIELDS
Physical Review D
Volume 113, Issue 064055, Page 21
2026 March
