Pulsar timing array stochastic background from light Kaluza-Klein resonances

Abstract

We investigate the potential of the warped extradimension framework as an explanation for the recently observed stochastic gravitational background at nHz frequencies in pulsar timing arrays (PTA). Our analysis reveals that the PTA data can be effectively accommodated by a first-order phase transition triggered by a radion at the MeV-GeV scale feebly coupled to the Standard Model. Remarkably, this outcome remains robust irrespective of the specific details of the warped extradimension embedding, providing a foundation for future investigations aiming to develop concrete extradimension descriptions of Nature. We also demonstrate that many existing embeddings are not viable, as their radion and graviton phenomenology clash with a MeV–GeV scale radion. As a possible way out, we sketch a promising solution involving multiple branes, wherein the light radion, graviton, and ensuing light resonances remain consistent with collider bounds and gravity tests.