Limits on the magnetic moment of sterile neutrino and two-photon neutrino decay

Abstract

It is shown that the non-zero transition magnetic moment ($μ_{tran}$) between the sterile neutrino ($ν_{s}$) and the muon neutrino ($ν_μ$) could be effectively searched for via the Primakoff effect, in the process of $ν_μ Z \to ν_{s}Z$ conversion in the external Coulomb field of a nucleus $Z$, with the subsequent $ν_{s}\to ν_μ + γ$ decay. From the recent results of the NOMAD neutrino detector at CERN a model-independent constraint of $μ_{tran} < (10^{-6} - 10^{-9}) μ_{B}$ is obtained depending on the value of $ν_{s}$ mass. For the $m_{s}\sim O(1) GeV$ region these bounds are comparable with the present experimental ones on $ν_μ$ and $ν_{e}$ diagonal magnetic moments and are more sensitive than those on $ν_τ$ magnetic moment. From the same analysis the constraint on $ν_τ(ν_{s})\to ν_μ +γ+ γ$ decay lifetime $τ> 2\times10^{13} sec/m_ν^{7}(MeV)$ is obtained. The limit is valid for neutrino masses up to $m_ν\sim O(1)GeV$.