Dilatonic effects on a falling test mass in scalar-tensor theory

Effects of a 4d dilaton field on a falling test mass are examined from the Einstein frame perspective of scalar-tensor theory. Results are obtained for the centripetal acceleration of particles in circular orbits, and the radial acceleration for particles with pure radial motion. These results are applied to the specific case of nonrelativistic motion in the weak field approximation of Brans-Dicke theory, employing the exact Xanthopoulos-Zannias solutions. For a given parameter range, the results obtained from Brans-Dicke theory are qualitatively dramatically different from those of general relativity. Comments are made concerning a comparison with the general relativistic results in the limit of an infinite Brans-Dicke parameter.