Structure of Neutron Stars in Tensor-Vector-Scalar Theory

TL;DR

This paper models neutron stars within TeVeS gravity to identify observable differences from General Relativity, providing potential tests for alternative gravity theories through neutron star properties and future observations.

Contribution

It develops neutron star models in TeVeS, analyzing how free parameters affect their structure and proposing observational tests to distinguish TeVeS from GR.

Findings

Causality constraints limit scalar field values in neutron stars.

Neutron star radii can significantly differ in TeVeS from GR.

Future electromagnetic and gravitational wave observations can test TeVeS predictions.

Abstract

Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success in explaining various phenomena without the need for dark matter. However, it is difficult to observationally discern the differences between TeVeS and predictions made within the Lambda-cold dark matter concordance model. This implies that alternative tests are required that independently verify which theory is correct. For this we turn to the strong-field regime of TeVeS. In particular, we solve the spherically symmetric equations of hydrostatic equilibrium for a perfect fluid with a realistic equation of state to build models of neutron stars in TeVeS. We show that causality within the neutron star is only maintained for certain cosmological values of the scalar field, which allows us to put constraints on this value independently of cosmological observations. We also discuss in detail the internal structure of neutron stars and how each of the free parameters in the theory effects the overall size and mass of the neutron stars. In particular, the radii of neutron stars in TeVeS can significantly differ from those in General Relativity for certain values of the vector field coupling, which allows us to also place extra constraints on this parameter. Finally, we discuss future observations of neutron stars using both the electromagnetic and gravitational wave spectrums that will allow for tests of the appropriate theory of gravity.