Linearized Horndeski Theory with a Potential in the Solar System Regime

Abstract

In this paper, the weak-field behavior of linearized Horndeski theory is studied, with emphasis on the role of a scalar potential with a nonvanishing minimum. In this regime, the minimum of the potential acts as an effective source of background curvature and produces a contribution similar to a cosmological constant. The analysis is restricted to the linear approximation, where nonlinear screening effects such as the Vainshtein mechanism can be consistently neglected. Within this framework, the consistency of the theory with Solar-System phenomenology in the weak-field limit is examined, and possible deviations from General Relativity depending on the model parameters are discussed. To this end, the linearized field equations for a static point mass are derived, the corresponding geodesic motion is investigated, and the resulting weak-field effects in classical Solar-System observables, including perihelion advance, light deflection, and gravitational redshift, are analyzed. The analysis further focuses on the limiting regimes of very light and very heavy scalar fields. In the very light scalar field regime, consistency with Solar System phenomenology requires sufficiently large values of the coupling parameter zeta, thereby suppressing the scalar contribution at local scales and keeping deviations from General Relativity negligible. In the very heavy scalar field regime, the scalar-mediated interaction acquires a short range and becomes dynamically suppressed, leading to weak-field predictions that are practically indistinguishable from those of General Relativity. Nevertheless, geometric terms associated with the minimum of the scalar potential may persist at linear order in the metric perturbations, depending on the value of zeta.