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Register a new userTesting neutrino magnetic moments with AGNs
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We propose to test the magnetic transition moments of Majorana neutrinos by comparing the fluxes of different flavours of neutrinos coming from active galactic nuclei (AGN). We show that, with reasonable assumptions about the magnetic field of the AGN, it is possible to obtain limits on $ u_{tau} u_{e}$ and $ u_{tau} u_{mu}$ transition moments which are three to five orders of magnitude better than the laboratory limits. We also point out that with certain parameter values the ratio $ u_{tau}/ u_{e,mu}$, when measured from different sources, is expected to vary from zero to values somewhat higher than one, providing an unambigious signal of a magnetic transition within the AGN which cannot be explained by neutrino oscillations.
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We explore the potential of current and next generation of coherent elastic neutrino-nucleus scattering (CE$ u$NS) experiments in probing neutrino electromagnetic interactions. On the basis of a thorough statistical analysis, we determine the sensitivities on each component of the Majorana neutrino transition magnetic moment (TMM), $left vert Lambda_i right vert$, that follow from low-energy neutrino-nucleus experiments. We derive the sensitivity to neutrino TMM from the first CE$ u$NS measurement by the COHERENT experiment, at the Spallation Neutron Source. We also present results for the next phases of COHERENT using HPGe, LAr and NaI[Tl] detectors and for reactor neutrino experiments such as CONUS, CONNIE, MINER, TEXONO and RED100. The role of the CP violating phases in each case is also briefly discussed. We conclude that future CE$ u$NS experiments with low-threshold capabilities can improve current TMM limits obtained from Borexino data.
Recent experiment proposed to observe induced radiative neutrino transitions are confronted to existing bounds on neutrino magnetic moments from earth-based experiments. These are found to exclude any observation by several orders of magnitude, unless the magnetic moments are assumed to be strongly momentum dependent. This possibility is discussed in some generality, and we find that nontrivial dependence of the neutrino form factor may indeed occur, leading to quite unexpected effects, although this is insufficient by orders of magnitude to justify the experiments.
The recent puzzling results of the XENON1T collaboration at few keV electronic recoils could be due to the scattering of solar neutrinos endowed with finite Majorana transition magnetic moments (TMMs). Within such general formalism, we find that the observed excess in the XENON1T data agrees well with this interpretation. The required TMM strengths lie within the limits set by current experiments, such as Borexino, specially when one takes into account a possible tritium contamination.
A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of $mu_{ u}^{eff}$ $<$ 2.8$cdot$10$^{-11}$ $mu_{B}$ at 90% c.l. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments.Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.
We show that a unified framework based on an $SU(2)_H$ horizontal symmetry which generates a naturally large neutrino transition magnetic moment and explains the XENON1T electron recoil excess also predicts a positive shift in the muon anomalous magnetic moment. This shift is of the right magnitude to be consistent with the Brookhaven measurement as well as the recent Fermilab measurement of the muon $g-2$. A relatively light neutral scalar from a Higgs doublet with mass near 100 GeV contributes to muon $g-2$, while its charged partner induces the neutrino magnetic moment. We analyze the collider tests of this framework and find that the HL-LHC can probe the entire parameter space of these models.
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