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Register a new userAccess to improve the muon mass and magnetic moment anomaly via the bound-muon $g$ factor
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A theoretical description of the $g$ factor of a muon bound in a nuclear potential is presented. One-loop self-energy and multi-loop vacuum polarization corrections are calculated, taking into account the interaction with the binding potential exactly. Nuclear effects on the bound-muon $g$ factor are also evaluated. We put forward the measurement of the bound-muon $g$ factor via the continuous Stern-Gerlach effect as an independent means to determine the free muons magnetic moment anomaly and mass. The scheme presented enables to increase the accuracy of the mass by more than an order of magnitude.
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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.
The spin dynamics in constant electromagnetic fields is described by the Bargmann-Michel-Telegdi equation which can be upgraded with anomalous magnetic and electric dipole moments. The upgraded equation remains self-consistent, Lorentz-covariant and gauge-invariant. It and its different forms have been confirmed in numerous experiments to high degree of accuracy. We have recently derived the spin motion equation within the Wentzel-Kramers-Brillouin weak-field approximation which adds a pseudoscalar correction to the BMT equation. The upgraded equation is again self-consistent, Lorentz-covariant, gauge-invariant, and free of unwanted artifacts. The pseudoscalar correction is expected to be small, and might become important in hypersensitive experiments, like the measurements of electric dipole moments which are themselves related to pseudoscalar quantities. It also becomes possible to explain why EDMs are so difficult to measure, since this correction term might lead to the effective screening of electric dipole moments. Within the same model, it is possible to explain the discrepancy between experimental and theoretical values of muon magnetic anomaly under assumption that the pseudoscalar correction is the dominant source of this discrepancy.
The long-standing muon $g-2$ anomaly has been confirmed recently at the Fermilab. The combined discrepancy from Fermilab and Brookhaven results shows a difference from the theory at a significance of 4.2 $sigma$. In addition, the LHC has updated the lower mass bound of a pure wino. In this letter, we study to what extent the $g-2$ can be explained in anomaly mediation scenarios, where the pure wino is the dominant dark matter component. To this end, we derive some model-independent constraints on the particle spectra and $g-2$. We find that the $g-2$ explanation at the 1$sigma$ level is driven into a corner if the higgsino threshold correction is suppressed. On the contrary, if the threshold correction is sizable, the $g-2$ can be explained. In the whole viable parameter region, the gluino mass is at most $2-4,$TeV, the bino mass is at most $2,$TeV, and the wino dark matter mass is at most $1-2,$TeV. If the muon $g-2$ anomaly is explained in the anomaly mediation scenarios, colliders and indirect search for the dark matter may find further pieces of evidence in the near future. Possible UV models for the large threshold corrections are discussed.
The present work introduces two possible extensions of the Standard Model Higgs sector. In the first case, the Zee-Babu type model for the generation of neutrino mass is augmented with a scalar triplet and additional singly charged scalar singlets. The second scenario, on the other hand, generalizes the Type-II seesaw model by replicating the number of the scalar triplets. A $mathbb{Z}_3$ symmetry is imposed in case of both the scenarios, but, allowed to be violated by terms of mass dimension two and three for generating neutrino masses and mixings. We examine how the models so introduced can explain the experimental observation on the muon anomalous magnetic moment. We estimate the two-loop contribution to neutrino mass induced by the scalar triplet, in addition to what comes from the doubly charged singlet in the usual Zee-Babu framework, in the first model. On the other hand, the neutrino mass arises in the usual Type-II fashion in the second model. In addition, the role of the $mathbb{Z}_3$ symmetry in suppressing lepton flavor violation is also elucidated.
The Fermilab Muon $g-2$ collaboration recently announced the first result of measurement of the muon anomalous magnetic moment ($g-2$), which confirmed the previous result at the Brookhaven National Laboratory and thus the discrepancy with its Standard Model prediction. We revisit low-scale supersymmetric models that are naturally capable to solve the muon $g-2$ anomaly, focusing on two distinct scenarios: chargino-contribution dominated and pure-bino-contribution dominated scenarios. It is shown that the slepton pair-production searches have excluded broad parameter spaces for both two scenarios, but they are not closed yet. For the chargino-dominated scenario, the models with $m_{tilde{mu}_{rm L}}gtrsim m_{tilde{chi}^{pm}_1}$ are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low $tan beta$ with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with $m_{tilde{mu}}lesssim 230$ GeV can explain the $g-2$ anomaly while satisfying the LHC constraints. Furthermore, we checked that the stau-bino coannihilation works properly to realize the bino thermal relic dark matter. We also investigate heavy staus case for the bino-dominated scenario, where the parameter region that can explain the muon $g-2$ anomaly is stretched to $m_{tilde{mu}}lesssim 1.3$ TeV.
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