Extended reduced-order surrogate models for scalar-tensor gravity in the strong field and applications to binary pulsars and gravitational waves

TL;DR

This paper develops a fast, accurate surrogate model for scalar-tensor gravity theories, enabling efficient testing of neutron star properties and strong-field gravity constraints using binary pulsar data.

Contribution

The authors created a reduced order surrogate model for DEF scalar-tensor gravity, significantly speeding up calculations while maintaining high accuracy, and applied it to constrain gravity theories with pulsar data.

Findings

Achieved two to three orders of magnitude speedup in calculations.

Provided the most stringent constraints on DEF theory to date.

Developed a publicly available tool for testing gravity in strong-field regimes.

Abstract

Statistically sound tests of scalar-tensor gravity theories in the strong-field regime usually involves computationally intensive calculations. In this study, we construct a reduced order surrogate model for the scalar-tensor gravity of Damour and Esposito-Far\`ese (DEF) with spontaneous scalarization phenomena developed for neutron stars (NSs). This model allows us to perform a rapid and comprehensive prediction of NS properties, including mass, radius, moment of inertia, effective scalar coupling, and two extra coupling parameters. We code the model in the pySTGROMX package, as an extension of our previous work, that speeds up the calculations at two and even three orders of magnitude and yet still keeps accuracy of $\sim1\%$. Using the model, we can calculate all the post-Keplerian parameters in the timing of binary pulsars conveniently, which provides a quick approach for us to place comprehensive constraints on the DEF theory. We perform Markov-chain Monte Carlo simulations with the model to constrain the parameters of the DEF theory with well-timed binary pulsars. Utilizing five NS-white dwarf and three NS-NS binaries, we obtain the most stringent constraints on the DEF theory up to now. Our work provides a public tool for quick evaluation of NSs' derived parameters to test gravity in the strong-field regime.