Novel probe of graviton dispersion relations at nanohertz frequencies

Abstract

We generalize Phinney’s “practical theorem” to account for modified graviton dispersion relations motivated by certain cosmological scenarios. Focusing on specific examples, we show how such modifications can induce characteristic localized distortions—bumps—in the frequency profile of the stochastic gravitational wave background emitted from distant binary sources. We concentrate on gravitational waves at nanohertz frequencies probed by pulsar timing arrays, and we forecast the capabilities of future experiments to accurately probe parameters controlling modified dispersion relations. Our predictions are based on properties of gravitational waves emitted in the first inspiral phase of the binary process and do not rely on assumptions of nonlinear effects occurring during the binary merging phase. Published by the American Physical Society 2024