Magnetic moments of active and sterile neutrinos in the laboratory, astrophysics, and cosmology

Author / Creator

Vassh, Nicole, author

Available as

Online

Physical

Summary

Since most of the neutrino parameters are well-measured, we illustrate precisely the prediction of the Standard Model, minimally extended to allow massive neutrinos, for the electron neutrino magne...

Since most of the neutrino parameters are well-measured, we illustrate precisely the prediction of the Standard Model, minimally extended to allow massive neutrinos, for the electron neutrino magnetic moment. We elaborate on the effects of light sterile neutrinos on the effective electron neutrino magnetic moment measured at the reactors. We explicitly show that the kinematical effects of the neutrino masses are negligible for active and light (eV) sterile neutrinos. We then demonstrate that the interpretation of the recently detected unidentified emission line in the X-ray spectrum of galaxy clusters to be due to the electromagnetic decay of a 7.1 keV sterile neutrino with a "mixing angle" of $\sin^2 2\theta \sim 6.8\times 10^{-11}$ implies the dipole moments of a fourth mass eigenstate to be on the order of $10^{-20}\mu_B$. Lastly, we examine the physics of the early universe when Majorana neutrinos ($\nu_e$,$\nu_{\mu}$, $\nu_{\tau}$) possess transition magnetic moments. These extra couplings beyond the usual weak interaction couplings alter the way neutrinos decouple from the plasma of electrons/positrons and photons. We calculate how transition magnetic moment couplings modify neutrino decoupling temperatures, and then use a full weak, strong, and electromagnetic reaction network to compute corresponding changes in Big Bang Nucleosynthesis abundance yields. We find that light element abundances and other cosmological parameters are sensitive to magnetic couplings on the order of $10^{-10}\mu_B$. Given the recent analysis of sub-MeV Borexino data which constrains Majorana moments to the order of $10^{-11}\mu_B$ or less, we find that changes in cosmological parameters from magnetic contributions to neutrino decoupling temperatures are below the level of upcoming precision observations.

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