Constraining gravitational wave propagation using pulsar timing array correlations

Pulsar timing arrays (PTA) are a promising probe to the cosmologically novel nanohertz gravitational wave (GW) regime through the stochastic GW background. In this work, we consider subluminal GW modes as a possible source of correlations in a PTA, utilizing the public code PTAfast and the 12.5 years correlations data by NANOGrav, which we hypothesize are sourced by GWs. Our results show no evidence in support of tensor-or vector-induced GW correlations in the data, and that vector correlations are disfavored. This places an upper bound to the graviton mass, mg < 10-22 eV, characteristic of the PTA GW energy scale.