Effect of the neutrino magnetic moment on the properties of the muon

The effect of the neutrino dipole magnetic moment on the properties of the muon is investigated within the standard model of electroweak interactions and a model based on the SU(2) _L × SU(2) _R × U(1) _B-L gauge group (left-right model). In the case of the Dirac neutrino, muon decay through the channel µ^? → e ^?γ is studied with allowance for the neutrino dipole magnetic moment. It is shown that, both in the standard model supplemented with an SU(2) _L right-handed neutrino singlet and in the standard model featuring two doublets of Higgs fields, radiative muon decay is unobservable. In the left-right model, the contributions of diagrams associated with the neutrino dipole magnetic moment become significant only in the case of a mutual compensation of the contributions of diagrams involving the electromagnetic vertices of charged gauge bosons and singly charged Higgs bosons. At specific values of the parameters of the left-right model, one can then obtain an experimental upper limit on the branching fraction of this reaction. The contributions of the neutrino dipole magnetic moment to the muon anomalous magnetic moment are found for the Dirac and the Majorana neutrino. It is established that, both in the standard model and in the left-right model, values of the neutrino anomalous magnetic moment that are required for explaining the (g ? 2)_µ anomaly are in excess of the theoretical predictions for this moment.     

Influence of the minimal supersymmetric standard model extended by an additional Higgs singlet on the anomalous magnetic moment of the muon

We present the results of the influence of the minimal supersymmetric standard model with an additional Higgs singletN, with vacuum expectation valuev _N, on the anomalous magnetic moment of the muon. This gives different mass matrices for the charginos and neutralinos, which are taken into account within the relevant penguin diagrams leading to a contribution Δa _μ to the anomalous magnetic moment of the muon. We show that a large vacuum expectation value for the Higgs singlet leads to a suppression of the supersymmetric contribution making it difficult to see in an experiment in the near future.     

Anomalously strong relaxation of the polarization of muons in the magnetically ordered and paramagnetic states of the TbMnO<Subscript>3</Subscript> multiferroic

An anomalously strong relaxation of the muon polarization in a magnetically ordered state in the TbMnO₃ multiferroic has been revealed by the method below the μSR Néel temperature (42 K). Such a relaxation is due to the muon channel of relaxation of the polarization and the interaction of the magnetic moment of the muon with inhomogeneities of the internal magnetic field of an ordered state in the form of a cycloid. Above the Néel temperature, beginning with temperatures depending on the applied magnetic field, a two-phase state has been revealed where one phase has an anomalously strong relaxation of the muon polarization for a paramagnetic state. These features of the paramagnetic state are due to short-range magnetic order domains that appear in strongly frustrated TbMnO₃. A true paramagnetic state has been observed only at T ≥ 150 K.     

Measurement of the magnetic moment of a negative muon in zinc and cadmium

The magnetic moment (g factor) of a negative muon on the 1s atomic levels of zinc and cadmium was measured with an accuracy higher by a factor of 7 than the accuracy achieved in other measurements. The experimental value of the g factor differs substantially from the theoretical results. Possible causes of this discrepancy are discussed.     

An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment

We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e ⁺e^- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment, the next-to-leading order results related to the vacuum polarization function are accurately reproduced. The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed. Received: 14 December 2001 / Published online: 7 June 2002     

Relaxation of the shallow acceptor center in germanium

Polarized negative muons were used to study relaxation mechanisms of shallow acceptors in germanium. In p-type germanium at low temperatures relaxation of the muon spin was observed, indicating that the muonic atom (gallium-like acceptor center) formed via capture of the negative muon by a host atom is in the paramagnetic state and its magnetic moment is relaxing. The relaxation rate of the muon spin was found to depend on temperature and on concentration of gallium impurity. We conclude that to the relaxation of the magnetic moment of the Ga acceptor in Ge there contribute both scattering of phonons and quadrupole interaction between the acceptors. We estimate, for the first time, the hyperfine interaction constant for the gallium acceptor in germanium as 0.11 MHz.     

Contributions to the muon’s anomalous magnetic moment from a hidden sector

The measurement of the anomalous magnetic moment of the muon provides a stringent test of the standard model and of any physics that lies beyond it. There is currently a deviation of 3.1σ between the standard model prediction for the muon’s anomalous magnetic moment and its experimental value. We calculate the contribution to the anomalous magnetic moment in theories where the muon couples to a particle in a hidden sector (that is, uncharged under the standard model) and a connector (which has nontrivial standard model gauge and hidden sector quantum numbers).     

Estimating scalar-leptoquark masses from the muon anomalous magnetic moment within the four-color symmetry model

The contributions to the muon anomalous magnetic moment from the doublets of scalar leptoquarks having a four-color origin are studied. It is shown that experimental data on the muon anomalous magnetic moment are compatible with the existence of relatively light scalar leptoquarks (of mass about 1 TeV or below).     

Letter: Antisymmetric Tensor Contribution to the Muon g − 2

We investigate the Kalb-Ramond antisymmetric tensor field as a solution to the muon g – 2 problem. In particular we calculate the lowest-order Kalb-Ramond contribution to the muon anomalous magnetic moment and find that we can fit the new experimental value for the anomaly by adjusting the coupling without affecting the electron anomalous magnetic moment results.     

Nonconservation of muon number in a model of lepton structure

We speculate on a possible primary structure for leptons similar to the quark structure for hadrons, and thus propose a new possible approach to the study of these particles. A suppression mechanism is provided for the effects of the new interaction upon the muon anomalous magnetic moment and in the decay amplitude for μ → eγ.     

On the production of a lepton pair in the collision of ultrarelativistic neutral particle with nonzero magnetic moment with nuclei

Explicit formulas which describe muon pair production in reaction γν→μ⁺μ⁻ν through neutrino magnetic moment are obtained and used to derive in the leading approximation cross section of muon pair production in νN-scattering due to neutrino magnetic moment. This cross section appears to be proportional to log⁴E_ν. Comparison with experimental data on tridents production provides an upper bound μ_νμ<4×10⁻⁸μ_B, which is approximately two orders of magnitude weaker than that from ν_μe elastic scattering data.     

Pionic contribution to the muon magnetic moment

A procedure is developed to derive an optimal lower bounds for the pionic contribution to the muon magnetic moment from analyticity of the pion form factor F(t), its normalization F(0)=1 and from experimental information from both the processes e^?p → e^?π⁺n and e⁺e^? → π⁺π^?. It represents essentially the solution of a certain kind of optimization problem in Hilbert space. Numerical results are presented and compared to the recent data for the muon magnetic moment; we find a_μ(π⁺π^?) ? 42 × 10^?9.     

Off-mass-shell muon anomalous magnetic moment

Interaction of charged leptons with photons is considered for the case when one of the lepton legs is off the mass shell. The effect due to off-mass-shell shift in the anomalous magnetic moment is computed within one-loop approximation. Possible contributions of this effect in the muon g — 2 measurements are discussed.     

Low energy supergravity and the anomalous magnetic moment of the muon

The anomalous magnetic moment of the muon (g ? 2)_μ imposes constraints on the masses and mixings of spin-zero leptons, gauge fermions, and Higgs fermions in minimal models of low energy supergravity. We demonstrate that there exist only limited values of the parameters in these models that are ruled out by existing limits on (g ? 2)_μ.     

Effects of magnetic structure distortion near a μ + meson in μSR spectroscopy

Possible effects of strong local anisotropy in the vicinity of a μ meson occupying a rare-earth metal interstitial site are considered. The distortion of the magnetic structure and the corresponding contribution to the dipolar field at the muon are calculated. A threshold-type change of the dipolar field depending on the local anisotropy or external magnetic field is predicted for the case where the direction toward the muon is perpendicular to the magnetic moment of one in the ions. The possibility of existence of two strengths of the dipolar field for the ferromagnetic phases of Dy and Tb, and of its abrupt change depending on the direction of the magnetic moment of the plane is predicted for helical antiferromagnetic structures. Fiz. Tverd. Tela (St. Petersburg) 40, 1298–1304 (July 1998)     

Correlation between muonic levels and nuclear structure in muonic atoms

A method that deals with the nucleons and the muon unitedly is employed to investigate the muonic lead, with which the correlation between the muon and nucleus can be studied distinctly. A “kink” appears in the muonic isotope shift at a neutron magic number where the nuclear shell structure plays a key role. This behavior may have very important implications for the experimentally probing the shell structure of the nuclei far away from the β-stable line. We investigate the variations of the nuclear structure due to the interaction with the muon in the muonic atom and find that the nuclear structure remains basically unaltered. Therefore, the muon is a clean and reliable probe for studying the nuclear structure. In addition, a correction that the muon-induced slight change in the proton density distribution in turn shifts the muonic levels is investigated. This correction to muonic level is as important as the Lamb shift and high order vacuum polarization correction, but is larger than anomalous magnetic moment and electron shielding correction.     

Weak corrections to the muon magnetic moment in a renormalizable gauge

A renormalizable gauge calculation of the weak corrections to the muon magnetic moment in Weinberg's model is presented. The calculation is performed in the context of the recently developed theory of non-Abelian gauge fields.     

The muon magnetic moment and new physics

The impact of the muon magnetic moment measurement on physics beyond the Standard Model is briefly reviewed. Particular emphasis is given on the case of supersymmetry. The sensitivity of g ? 2 to supersymmetry parameters and the potential for model discrimination and parameter measurements is described. The interplay between LHC data on the Higgs boson, limits on new particles, and g ? 2 is discussed.     

Muon g - 2 in the Littlest Higgs Model

In this paper the anomalous magnetic dipole moment of muon in the littlest Higgs (LH) model is studied at one-loop level. We discuss the dependence of the contributions on the global symmetry breaking scale f, mixing angles c and cˊ, and the Higgs triplet vacuum expectation value vˊ in the electroweak precision data preferring ranges. We find that the LH model can give a relatively small, but non-negligible extra weak contribution to the muon anomalous magnetic moment and can reduce the deviation of Δa_μ from 2.6σ for the SM to 2.5σ for the LH model.     

Muon anomalous magnetic moment: A consistency check for the next-to-leading-order hadronic contributions

A duality-inspired model for verifying a consistency of the evaluation of the next-to-leadingorder hadronic contributions to the muon anomalous magnetic moment with that of the leading-order ones is proposed. A part of the next-to-leading-order hadronic contributions related to the photon vacuum polarization function is rather accurately reproduced in the model. I find a new numerical value for the light-by-light hadronic contribution that leads to the agreement of the Standard Model theoretical prediction for the muon anomalous magnetic moment with the recent experimental result.