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

Abstract

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

Comments: 13 pages, LaTex, 2 eps fugures included. 2 references are added. Submitted to Phys. Lett. B