Implications of a Massless Neutralino for Neutrino Physics

TL;DR

The paper proposes that a (nearly) massless neutralino can act as a sterile neutrino that couples to right-handed neutrinos through a soft SUSY-breaking term $c \tilde B N$, yielding a see-saw–driven contribution to light-neutrino masses with $m_{\nu_0} \sim c^2 / M_M$. By allowing nonuniversal gaugino masses in the MSSM or a mostly singlino neutralino in the NMSSM, a massless neutralino can be phenomenologically viable, with suppressed $Z$-width couplings satisfying LEP constraints. The sterile neutrino participates in neutrino phenomenology, providing a natural mechanism to explain the LSND anomaly and achieve large mixing among active flavors, albeit at the cost of fine-tuning. Overall, the work connects the soft SUSY-breaking scale to measurable neutrino properties, offering a novel sterile-neutrino framework within MSSM/NMSSM contexts.

Abstract

We consider the phenomenological implications of a soft SUSY breaking term BN at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed neutrino field). In models with a massless (or nearly massless) neutralino, such a term will give rise through the see-saw mechanism to new contributions to the mass matrix of the light neutrinos. We treat the massless neutralino as an (almost) sterile neutrino and find that its mass depends on the square of the soft SUSY breaking scale, with interesting consequences for neutrino physics. We also show that, although it requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not experimentally excluded. The implications of this scenario for neutrino physics are discussed.