# Testing the Gravitational Weak Equivalence Principle in the Standard-Model Extension with Binary Pulsars

## TL;DR

This paper establishes experimental bounds on nonlinear Lorentz-violating terms in gravity using binary pulsar data, testing the gravitational weak equivalence principle within the Standard-Model Extension framework.

## Contribution

It provides the first constraints on nonlinear anisotropic curvature couplings that violate the GWEP, expanding tests of Lorentz symmetry in gravity beyond linearized theories.

## Key findings

- Boundaries set on nonlinear Lorentz-violating gravity terms
- Binary pulsar timing constrains body-dependent accelerations
- First test of GWEP violation in a fully anisotropic Lorentz-violating framework

## Abstract

The Standard-Model Extension provides a framework to systematically investigate possible violation of the Lorentz symmetry. Concerning gravity, the linearized version was extensively examined. We here cast the first set of experimental bounds on the nonlinear terms in the field equation from the anisotropic cubic curvature couplings. These terms introduce body-dependent accelerations for self-gravitating objects, thus violating the gravitational weak equivalence principle (GWEP). Novel phenomena, that are absent in the linearized gravity, remain experimentally unexplored. We constrain them with precise binary-orbit measurements from pulsar timing, wherein the high density and large compactness of neutron stars are crucial for the test. It is the first study that seeks GWEP-violating signals in a fully anisotropic framework with Lorentz violation.