Searching for Alternative Polarizations of Gravity Using Pulsar Timing Arrays

The unprecedented sensitivity to low-frequency gravitational waves (GWs) achieved by the most recent data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) attests to the value of pulsar timing in robust and sensitive tests of gravity, including tests for exotic polarizations of GWs. By providing a different line of sight to each pulsar along with an enhanced response to scalar-longitudinal modes, pulsar timing proves to be a fertile ground for studying alternative polarizations of gravity. In this regard, we have developed a statistical and theoretical framework to search for all alternative polarizations of gravity stemming from various metric theories of spacetime using NANOGrav’s 12.5 year data set. Using this advanced framework, we search for evidence of GW polarizations not present in Einstein’s general relativity and place constraints on the amplitudes of these GW modes.