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

Statistically sound tests of scalar-tensor gravity theories in the strong-field regime usually involve computationally intensive calculations. In this study, we construct a reduced order surrogate model for the scalar-tensor gravity of Damour and Esposito-Fare`se (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, which speeds up the calculations at 2 and even 3 orders of magnitude and yet still keeps accuracy of similar to 1%. 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.

Automated summary

A reduced order surrogate model was constructed for scalar-tensor gravity theories, allowing for rapid prediction of neutron star properties. This model significantly speeds up calculations while maintaining accuracy, and is utilized to constrain parameters of the DEF theory through well-timed binary pulsars. The study provides the most stringent constraints on the DEF theory to date and offers a public tool for quick evaluation of neutron stars' derived parameters for testing gravity in the strong-field regime.