Large neutrino magnetic moments in the light of recent experiments
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Springer
Received: July 14, 2020 Accepted: September 13, 2020 Published: October 7, 2020
K.S. Babu,a Sudip Janab and Manfred Lindnerb a
Department of Physics, Oklahoma State University, Stillwater, OK 74078, U.S.A. b Max-Planck-Institut f¨ ur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
E-mail: [email protected], [email protected], [email protected] Abstract: The excess in electron recoil events reported recently by the XENON1T experiment may be interpreted as evidence for a sizable transition magnetic moment µνe νµ of Majorana neutrinos. We show the consistency of this scenario when a single component transition magnetic moment takes values µνe νµ ∈ (1.65–3.42) × 10−11 µB . Such a large value typically leads to unacceptably large neutrino masses. In this paper we show that new leptonic symmetries can solve this problem and demonstrate this with several examples. We first revive and then propose a simplified model based on SU(2)H horizontal symmetry. Owing to the difference in their Lorentz structures, in the SU(2) H symmetric limit, mν vanishes while µνe νµ is nonzero. Our simplified model is based on an approximate SU(2)H , which we also generalize to a three family SU(3)H -symmetry. Collider and low energy tests of these models are analyzed. We have also analyzed implications of the XENON1T data for the Zee model and its extensions which naturally generate a large µνe νµ with suppressed mν via a spin symmetry mechanism, but found that the induced µνe νµ is not large enough to explain recent data. Finally, we suggest a mechanism to evade stringent astrophysical limits on neutrino magnetic moments arising from stellar evolution by inducing a medium-dependent mass for the neutrino. Keywords: Beyond Standard Model, Neutrino Physics ArXiv ePrint: 2007.04291
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)040
JHEP10(2020)040
Large neutrino magnetic moments in the light of recent experiments
Contents 1 Introduction
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2 Neutrino magnetic moments: the experimental situation 2.1 XENON1T 2.2 Experimental searches for neutrino magnetic moments 2.3 Limits on µν from astrophysics and cosmology
3 4 6 7 7 7 9 10 10
4 SU(2)H model for large neutrino magnetic moment 4.1 Neutrino transition magnetic moment 4.2 Breaking of SU(2)H symmetry and induced neutrino mass
11 13 15
5 Phenomenological implications of SU(2)H model 5.1 Modifications to τ decay 5.2 LEP constraints 5.3 LHC prospects 5.4 Non-standard interactions and IceCube
18 18 19 21 23
6 Generalization to SU(3)H horizontal symmetry 6.1 Collider signals
25 27
7 Neutrino magnetic moment in the Zee model
28
8 Mechanism to evade astrophysical limits on neutrino magnetic moments 32 9 Summary and conclusions
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Introduction
The XENON collaboration has recently performed a search for new physics with lowenergy electronic recoil data recorded with the XENON1T detector and reported an excess of events over the known backgrounds in the recoil energy range (1–7) keV, peaked around 2.5 keV [1]. T
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