Detecting non-GR polarization states of continuous gravitational waves with pulsar timing arrays

Pulsar timing arrays are sensitive to resolvable supermassive black hole binaries in the very early inspiral phase. Modified gravity theories allow for the emission of gravitational dipole radiation, which appears at -1 post-Newtonian order relative to the leading GR contribution, making the very early inspiral an opportune regime to test for the presence of modified gravity effects. Using a theory-agnostic generalization of modified gravity theories based on the parametrized post-Einsteinian framework, we explore the efficiency of detecting non-GR polarization strains with simulated pulsar timing array data, and subsequently find their upper limits as a function of sky location.