Speaker
Description
Recent detection of stochastic gravitational wave background by pulsar timing arrays (PTAs) missions opens a new window of testing fundamental physics laws at energy scales far beyond what is reached by particle physics experiments and/or by astrophysical observations; I will discuss the PTAs data in the context of massive gravity independently of the gravitational wave signal origin (astrophysical or cosmological). More precisely, PTAs probe the stochastic gravitational wave background through the angular cross-correlations of timing residuals. For an isotropic tensor background in general relativity, the expected overlap reduction function (ORF) is the Hellings--Downs (HD) correlation. We investigate how a non-zero graviton mass modifies this prediction through a massive dispersion relation and additional vector and scalar polarizations, producing an effective ORF. We introduce a phenomenological scaling prescription, to ensure decoupling the vector and scalar sectors relative to the tensor sector in the massless limit, thereby ensuring that the ORF smoothly approaches the HD correlation as $m_g/\omega \to 0$. This prescription clarifies how to meaningfully compare the effective ORF in massive gravity with observed PTA angular correlations. Finally, I will address the NANOGrav 15 years dataset to determine how the graviton mass affects PTA timing-residual modeling.