Neutrino Transition Polarizability

Abstract

We study Neutrino Transition Polarizability, where a light pseudoscalar $\varphi$ couples active neutrinos to heavy neutral leptons $N$ and interacts with two photons. We consider an effective description of the active - sterile interaction, and a realization within the inverse seesaw mechanism; the coupling to photons is generated by heavy charged states. For $m_N>m_{\varphi }$, the decay $N\to \nu \varphi$ can greatly shorten the heavy neutrino lifetime, while $\varphi \to \gamma \gamma$ produces a displaced photon pair. This changes the relevant search strategies, favoring production and decay inside detectors. We discuss existing constraints and estimate the sensitivity of displaced photon searches at DUNE, Belle II, LHCb and FCC-ee, highlighting the complementarity of neutrino scattering and meson and electroweak boson decays.

arXiv comment36 pages, 24 figures