Tests of the universality of free fall for strongly self-gravitating bodies with radio pulsars

TL;DR

This paper reviews tests of the strong equivalence principle using pulsar-white dwarf systems, introduces a new method based on orbital eccentricity variation, and discusses future testing prospects with advanced systems.

Contribution

It presents a novel SEP violation test based on orbital eccentricity change, offering direct detection and improved precision over previous probabilistic methods.

Findings

Current pulsar timing provides the most precise SEP tests for strongly self-gravitating bodies.

The new de/dt measurement method is not affected by external effects, enhancing test reliability.

Future systems like globular clusters and triples could improve SEP violation constraints.

Abstract

In this paper, we review tests of the strong equivalence principle (SEP) derived from pulsar-white dwarf data. The extreme difference in binding energy between both components and the precise measurement of the orbital motion provided by pulsar timing allow the only current precision SEP tests for strongly self-gravitating bodies. We start by highlighting why such tests are conceptually important. We then review previous work where limits on SEP violation are obtained with an ensemble of wide binary systems with small eccentricity orbits. Then we propose a new SEP violation test based on the measurement of the variation of the orbital eccentricity de/dt. This new method has the following advantages: a) unlike previous methods it is not based on probabilistic considerations, b) it can make a direct detection of SEP violation, c) the measurement of de/dt is not contaminated by any known external effects, which implies that this SEP test is only restricted by the measurement precision of de/dt. In the final part of the review, we conceptually compare the SEP test with the test for dipolar radiation damping, a phenomenon closely related to SEP violation, and speculate on future prospects by new types of tests in globular clusters and future triple systems.