Testing General Relativity

Compact binary observations enable unique strong-field tests of General Relativity. Such tests are complicated by the lack of complete alternative frameworks or theories that have been as extensively studied as General Relativity. One aspect of our efforts focuses on constructing tests for the fundamental properties of gravitational waves, such as their polarization content.

We are also constructing a robust statistical framework for combining information on deviations from General Relativity from the dozens of compact binary observations currently available. Our framework relaxes common assumptions about expected deviations and instead targets the population distribution of potential beyond-General Relativity effects. A study led by Caltech graduate student Ethan Payne extended the framework to include the population distribution of the black hole masses and spins, thus fortifying our tests of General Relativity against astrophysics assumptions and systematics. This work led to the tightest constraint to date for the mass of the graviton with gravitational waves.

Caltech staff scientist Ryan Magee also led a study of the impact of selection effects on tests of General Relativity. Since searches for gravitational wave signals are based on waveforms predicted by General Relativity, it is possible that we are missing a large number of sources whose signals deviate strongly from General Relativity. Our results indicate that the impact of selection effects is in fact minimal for parametrized tests of the gravitational wave phase. Current constraints on deviations from General Relativity are already strong enough to make selection effects subdominant.