Large Neutrino Magnetic Moment Research Articles

Neutrino-antineutrino oscillations induced by strong magnetic fields in dense matter

We simulate neutrino-antineutrino oscillations caused by strong magnetic fields in dense matter. With the strong magnetic fields and large neutrino magnetic moments, Majorana neutrinos can reach flavor equilibrium. We find that the flavor equilibration of neutrino-antineutrino oscillations are sensitive to the values of the baryon density and the electron fraction inside the matter. The neutrino-antineutrino oscillations are suppressed in the case of the large baryon density in neutron- (proton)-rich matter. On the other hand, the flavor equilibration occurs when the electron fraction is close to 0.5 even in the large baryon density. From the simulations, we propose a necessary condition for the equilibration of neutrino-antineutrino oscillations in dense matter. We also study whether such a necessary condition is satisfied near the protoneutron star by using results of neutrino hydrodynamic simulations of core-collapse supernovae. In our explosion model, the flavor equilibration would be possible if the magnetic field on the surface of the protoneutron star were larger than ${10}^{14}\text{ }\text{ }\mathrm{G}$, which is the typical value of the magnetic fields of magnetars.

Large neutrino magnetic moments in the light of recent experiments

The excess in electron recoil events reported recently by the XENON1T experiment may be interpreted as evidence for a sizable transition magnetic moment {mu}_{v_e{v}_{mu }} of Majorana neutrinos. We show the consistency of this scenario when a single component transition magnetic moment takes values {mu}_{v_e{v}_{mu }}in left(1.65-3.42right)times {10}^{-11}{mu}_B . 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 {mu}_{v_e{v}_{mu }} 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 {mu}_{v_e{v}_{mu }} with suppressed mν via a spin symmetry mechanism, but found that the induced {mu}_{v_e{v}_{mu }} 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.

One-loop running of dimension-six Higgs-neutrino operators and implications of a large neutrino dipole moment

We compute the one-loop running of the dimension-six CP-even Higgs operators in the Standard Model effective field theory involving the right-handed component of the would-be Dirac neutrinos. Then, on the basis of naturalness arguments, for some operators we obtain bounds that surpass direct constraints by orders of magnitude. We also discuss the implications of a large Dirac neutrino magnetic dipole moment. In particular, we demonstrate that a neutrino magnetic moment explaining the recent XENON1T excess induces Higgs and Z invisible decays with branching ratios in the range [10−18, 10−12]. These numbers are unfortunately beyond the reach of current and near future facilities.

Revisiting large neutrino magnetic moments

Current experimental sensitivity on neutrino magnetic moments is many orders of magnitude above the Standard Model prediction. A potential measurement of next-generation experiments would therefore strongly request new physics beyond the Standard Model. However, large neutrino magnetic moments generically tend to induce large corrections to the neutrino masses and lead to fine-tuning. We show that in a model where neutrino masses are proportional to neutrino magnetic moments. We revisit, discuss and propose mechanisms that still provide theoretical consistent explanations for a potential measurement of large neutrino magnetic moments. We find only two viable mechanisms to realize large transition magnetic moments for Majorana neutrinos only.

Large neutrino magnetic moments in supersymmetry in light of the new data

We re-analyze the magnetic moments of Dirac and Majorana neutrinos in a supersymmetric extension of the MSSM with singlet right-handed neutrinos. We show that if one incorporates left–right slepton mixing, the neutrino magnetic moment becomes proportional to the corresponding lepton, rather than the neutrino, mass. Incorporating the new SuperKamiokande, the solar and the LSND data, the magnetic moments are larger than previous calculations indicate, and proportional to the tau mass, without invoking any additional symmetries or introducing any exotic particles. The supersymmetric contribution to the magnetic moments of either Dirac or Majorana neutrinos can become of order O(10 −12)μ B and therefore of interest experimentally.

Majorana Neutrino Transition Magnetic Moment in a Superstring Inspired MinimalE6Model

Majorana neutrino transition magnetic moments [MNTM] in a superstring inspired E 6 model are investigated. The additional fermions in the 27-plet of E 6 are shown to lead to a large enough MNTM for a reasonable choice of Yukawa couplings without imposing the additional `exotic' symmetries prevalent in most other models for large neutrino magnetic moments.

Two-loop Majorana neutrino mass and magnetic moment in a gauge model

Two-loop contributions to Majorana mass and transition magnetic moment in a gauge model not in conflict with decaying neutrino dark matter (DDM) hypothesis have been studied. Another variant of an earlier model [J Dhar and S Dev,Pramana — J. Phys.39 541 (1992)] consistent with the DDM hypothesis is proposed and is shown to lead to large enough neutrino magnetic moment and consistent with the phenomenological constraints on neutrino mass.

Search for massive, unstable photinos that violate R parity

A search for unstable, massive photinos pair produced in e+e− collisions has been performed using the OPAL detector at LEP. The data sample corresponds to an integrated luminosity of 21 pb−1 collected at center-of-mass energies near the Z0 resonance. The unstable photino is assumed to decay into τ±/gnl (l = e or μ) final states, thereby violating individual lepton numbers and R parity. This search is inspired by a particular model of supersymmetry which is of interest within the context of solar neutrino experiments because it allows for a large neutrino magnetic moment. The present search excludes a large portion of the parameter space allowed by the model.

Simple mechanism for large neutrino magnetic moments.

We show that the simple Zee model of the neutrino mass already incorporates the interesting prediction of a large transitional neutrino magnetic moment.Received 30 April 1992DOI:https://doi.org/10.1103/PhysRevD.46.2268©1992 American Physical Society

Unifiable model with large neutrino magnetic moment.

We present a model which embeds Voloshin symmetry to suppress neutrino masses while giving a large magnetic moment. A special feature of the model is that there is no neutrino mixing. The model can be easily embedded in a grand unified group, as we discuss.

Large neutrino magnetic moments and the existence of singly charged scalar fields.

A certain general mechanism by which the neutrinos can have large magnetic dipole moments ({ital d}{sub {nu}}{similar to}10{sup {minus}11}{mu}{sub {ital B}}) and small masses ({ital m}{sub {nu}}{lt}10{sup {minus}1} eV) is explored. It is found that it is characteristic of this mechanism that there exist singly charged singlet scalars (i.e., scalars in (1,1,+1) of SU(3){times}SU(2){times}U(1)) as in the Zee model of lepton-number violation. It is suggested that, since such scalars arise automatically in low-energy supersymmetry as scalar partners of the right-handed leptons, a large neutrino dipole moment may be a signal of supersymmetry.

Radiative fermion masses and large neutrino magnetic moment: A unified picture.

A large transition magnetic moment of the neutrino (needed to explain the apparent anticorrelation of the solar-neutrino flux with the sunspots) can be reconciled with a naturally small neutrino mass by gauging the horizontal SU(2) symmetry connecting the electron and the muon generations. In this paper, we show that the same symmetry, when extended to the quark sector, provides a radiative picture for fermion masses, thereby explaining qualitatively the observed mass and mixing hierarchy among charged fermions. The neutrino masses arise in the model only at the two-loop level, whereas the magnetic moment is a one-loop effect. The neutrino is predicted to be a pseudo Dirac particle with {ital m}{sub {nu}}{approx}1--10 eV and {delta}{ital m}{sub {nu}}{sup 2}{approx}10{sup {minus}7} eV{sup 2}.

Experimental consequences of a model for a neutrino magnetic moment.

We present an overview of the experimental consequences of a model proposed recently in order to explain the solar-neutrino puzzle. The model produces a large neutrino magnetic transition moment, with a neutrino mass that is naturally small. Most low-energy physics is unaffected. However, the electric dipole moment of the electron is generically near the present experimental bound, and deviations in \ensuremath{\tau} decays may be large enough to be observable in a \ensuremath{\tau} factory. At high energies it is possible to search directly for the new scalars predicted by the model. The scalars all decay leptonically, and are ideal for searches by hadron colliders, as well as by ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ machines. In particular, the model contains a pair of charged scalars with a mass above \ensuremath{\sim}25 GeV, which could still be found in CERN LEP. The other scalars must be heavier than \ensuremath{\sim}${\mathit{M}}_{\mathit{Z}}$/2, following the recent results from the SLAC Linear Collider, LEP, and the Fermilab Tevatron. These bounds will be considerably extended in CERN LEP II and the Superconducting Super Collider.

Supersymmetric model for neutrino magnetic transition moment

A supersymmetric model for a large neutrino magnetic moment is presented. The neutrino mass is protected by an approximate horizontal symmetry. The model possessed an unbroken ℓ e -ℓ μ symmetry which enforces the eqality of the electron and muon neutrino masses. We find that for a 10 eV neutrino, the neutrino can have a magnetic transition moment up to 10 −12 μ B without tuning of parameters. With tuning, the mass can be further suppressed or the magnetic moment correspondingly increased.

Mechanism for large neutrino magnetic moments.

A general mechanism, based on very simple considerations of spin, is proposed, which has the effect of enhancing the neutrino magnetic dipole moment relative to the neutrino mass.

Neutral current effects in a model with a naturally large neutrino magnetic moment

A phenomenological analysis is performed on the neutral current sector of a model recently proposed by Barbieri and Mohapatra, which predicts in a natural way a large electron neutrino magnetic moment. Limits on the mass and the mixing of an extra Z′ boson predicted by the model are extracted from the present measurements of the standard model ϱ parameter and from the present neutral current data. Prospects at LEP and future hadron colliders are also given.

A model for a large neutrino magnetic transition moment and naturally small mass

Models that attempt to solve the solar neutrino problem by producing a large neutrino magnetic moment, generally also produce neutrino mass corrections in the keV range, and therefore require fine tuning. Here, we construct a model for Majorana neutrinos with a Voloshin-type SU (2) horizontal symmetry that protects tge masses. This symmetry is broken only by terms of order g W(m μ−m e) 2M W ≅ 4×10 −4 , resulting in masses which are naturally of the order of a few eV. The difference between electron and muon lepton numbers is conserved, so that troubling rare decays like μ→ eγ and μ→3 e are forbidden. One may also demand tau lepton number conservation. Low energy effects are very difficult to observe, but the model has physical scalars which can be seen in colliders with a clear experimental signature.

Light neutrinos with large magnetic moments and the solar neutrino problem

We analyze the question of having a large enough neutrino magnetic moment in order to implement the VVO mechanism in the framework of an SU(4)×SU(2) L×SU(2) R model, derivable from four-dimensional superstrings. We find that the radiative corrections to the seesaw type neutrino mass matrix can generate an appreciable magnetic moment without any seesaw type suppression.

Solar neutrinos: Magnetic moments and masses

The Voloshin-Vysotski-Okun proposal of a large neutrino magnetic moment in the range (0.3−1)×10 −10 μ B as a solution to the solar neutrino problem is examined from the fundamental viewpoint of attempting to reconcile such values with the well-known smallness of neutrino masses. It is seen that the particle physics models that are able to implement the required neutrino magnetic moments for the VVO solution fail to provide small masses, thus questioning the realization of this attractive solution.