Model-Independent Comparisons of Pulsar Timings to Scalar-Tensor Gravity

TL;DR

This paper introduces a model-independent method for analyzing pulsar timing data to constrain scalar-tensor theories of gravity, providing bounds on stellar parameters that are independent of specific model assumptions.

Contribution

It presents a novel approach to directly fit pulsar timing data in terms of phenomenological star parameters, avoiding reliance on microscopic model details.

Findings

Bounds on pulsar masses and scalar charges at 68% confidence level.

Constraints are independent of scalar-tensor model specifics and stellar equations of state.

Results are consistent with existing limits for Brans-Dicke models.

Abstract

Observations of pulsar timing provide strong constraints on scalar-tensor theories of gravity, but these constraints are traditionally quoted as limits on the microscopic parameters (like the Brans-Dicke coupling, for example) that govern the strength of scalar-matter couplings at the particle level in particular models. Here we present fits to timing data for several pulsars directly in terms of the phenomenological couplings (masses, scalar charges, moment of inertia sensitivities and so on) of the stars involved, rather than to the more microscopic parameters of a specific model. For instance, for the double pulsar PSR J0737-3039A/B we find at the 68% confidence level that the masses are bounded by 1.28 < m_A/m_sun < 1.34 and 1.19 < m_B/m_sun < 1.25, while the scalar-charge to mass ratios satisfy |a_A| < 0.21, |a_B| < 0.21 and |a_B - a_A| < 0.002$. These constraints are independent of the details of the scalar tensor model involved, and of assumptions about the stellar equations of state. Our fits can be used to constrain a broad class of scalar tensor theories by computing the fit quantities as functions of the microscopic parameters in any particular model. For the Brans-Dicke and quasi-Brans-Dicke models, the constraints obtained in this manner are consistent with those quoted in the literature.