Orbital and epicyclic frequencies in massive scalar-tensor theory with self-interaction.

Observations of the electromagnetic signals originating from an accretion discs in the close vicinity of a compact object can be used to test spacetime in the strong field regime. More specifically, the so-called quasi-periodic oscillations, observed in the X-ray light curves of some pulsars, might carry features of the underlying theory of gravity making them a promising tool for testing the modifications of Einstein's theory. Although there are different ways of explaining the quasi-periodic oscillations, one thing most of the models have in common is that they incorporate in certain way the radius of the innermost stable circular orbit, and the orbital and the epicyclic frequencies of particles moving around the compact object. In this paper we study the aforementioned quantities in the context of massive scalar-tensor theory including self-interaction of the scalar field. Unlike the massless scalar field case, the neutron stars in these theories can have large deviations from pure general relativity for values of the free parameters that are in agreement with the observations. Thus the deviations in the orbital and epicyclic frequencies can reach large values. [ABSTRACT FROM AUTHOR]