Gravitational radiation from compact binary systems in the massive Brans-Dicke theory of gravity

TL;DR

This paper derives gravitational equations and observational bounds in a massive Brans-Dicke gravity theory, improving constraints on its parameters using Solar System and binary pulsar data.

Contribution

It provides the first detailed analysis of gravitational radiation and related effects in a massive Brans-Dicke theory, including new bounds from observational data.

Findings

Cassini measurements constrain D>40000 for m_s<2.5x10^{-20} eV

Lunar Laser Ranging constrains D>1000 for m_s<2.5x10^{-20} eV

Binary pulsar observations constrain D>1250 for m_s<10^{-20} eV

Abstract

We derive the equations of motion, the periastron shift, and the gravitational radiation damping for quasicircular compact binaries in a massive variant of the Brans-Dicke theory of gravity. We also study the Shapiro time delay and the Nordtvedt effect in this theory. By comparing with recent observational data, we put bounds on the two parameters of the theory: the Brans-Dicke coupling parameter \omega_{BD} and the scalar mass m_s. We find that the most stringent bounds come from Cassini measurements of the Shapiro time delay in the Solar System, that yield a lower bound \omega_{BD}>40000 for scalar masses m_s<2.5x10^{-20} eV, to 95% confidence. In comparison, observations of the Nordtvedt effect using Lunar Laser Ranging (LLR) experiments yield \omega_{BD}>1000 for m_s<2.5x10^{-20} eV. Observations of the orbital period derivative of the quasicircular white dwarf-neutron star binary PSR J1012+5307 yield \omega_{BD}>1250 for m_s<10^{-20} eV. A first estimate suggests that bounds comparable to the Shapiro time delay may come from observations of radiation damping in the eccentric white dwarf-neutron star binary PSR J1141-6545, but a quantitative prediction requires the extension of our work to eccentric orbits.