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Register a new userRadiative lepton mass and muon $g-2$ with suppressed lepton flavor and CP violations
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Wen Yin
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The recent experimental status, including the confirmation of the muon $g-2$ anomaly at Fermilab, indicates a Beyond Standard Model (BSM) satisfying the following properties: 1) it enhances the $g-2$ 2) suppresses flavor violations, such as $mu to e gamma$, 3) suppresses CP violations, such as the electron electric dipole moment (EDM). In this letter, I show that if the masses of heavy leptons are generated radiatively, the eigenbasis of the mass matrix and higher dimensional photon operators can be automatically aligned. As a result, the muon $g-2$ is enhanced but the EDM of the electron and $mu to e gamma$ rate are suppressed. Phenomenology and applications of the mechanism to the B-physics anomalies are argued.
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A systematic investigation on muon anomalous magnetic moment and related lepton flavor-violating process such as $mto eg$, $tto eg$ and $tto mg$ is made at two loop level in the models with flavor-changing scalar interactions. The two loop diagrams with double scalar exchanges are studied and their contributions are found to be compatible with the ones from Barr-Zee diagram. By comparing with the latest data, the allowed ranges for the relevant Yukawa couplings $Y_{ij}$ in lepton sector are obtained. The results show a hierarchical structure of $Y_{m e, t e} ll Y_{m t} simeq Y_{mm}$ in the physical basis if $Delta a_{mu}$ is found to be $>50times 10^{-11}$. It deviates from the widely used ansatz in which the off diagonal elements are proportional to the square root of the products of related fermion masses. An alternative Yukawa coupling matrix in the lepton sector is suggested to understand the current data. With such a reasonable Yukawa coupling ansatz, the decay rate of $tto mg$ is found to be near the current experiment upper bound.
We propose a leptoquark model with two scalar leptoquarks $S^{}_1 left( bar{3},1,frac{1}{3} right)$ and $widetilde{R}^{}_2 left(3,2,frac{1}{6} right)$ to give a combined explanation of neutrino masses, lepton flavor mixing and the anomaly of muon $g-2$, satisfying the constraints from the radiative decays of charged leptons. The neutrino masses are generated via one-loop corrections resulting from a mixing between $S^{}_1$ and $widetilde{R}^{}_2$. With a set of specific textures for the leptoquark Yukawa coupling matrices, the neutrino mass matrix possesses an approximate $mu$-$tau$ reflection symmetry with $left( M^{}_ u right)^{}_{ee} = 0$ only in favor of the normal neutrino mass ordering. We show that this model can successfully explain the anomaly of muon $g-2$ and current experimental neutrino oscillation data under the constraints from the radiative decays of charged leptons.
The stringent experimental bound on $mu rightarrow e gamma$ is compatible with a simultaneous and sizable new physics contribution to the electron and muon anomalous magnetic moments $(g-2)_ell$ ($ell=e,,mu$), only if we assume a non-trivial flavor structure of the dipole operator coefficients. We propose a mechanism in which the realization of the $(g-2)_ell$ correction is manifestly related to the mass generation through a flavor symmetry. A radiative flavon correction to the fermion mass gives a contribution to the anomalous magnetic moment. In this framework, we introduce a chiral enhancement from a non-trivial $mathcal{O}(1)$ quartic coupling of the scalar potential. We show that the muon and electron anomalies can be simultaneously explained in a vast region of the parameter space with predicted vector-like mediators of masses as large as $M_chiin [0.6,2.5]$~TeV.
The recent confirmation of the muon $g-2$ anomaly by the Fermilab g-2 experiment may harbinger a new era in $mu$ and $tau$ physics. As is known, the effect can arise from one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely $H$ and $A$, that have flavor changing neutral couplings $rho_{taumu}$ and $rho_{mutau}$ at $sim 20$ times the usual tau Weinberg coupling, $lambda_tau$. A similar diagram induces $mu to egamma$, where $rho_{etau}= rho_{tau e} = {cal O}(lambda_e)$ brings the rate right into the sensitivity of the MEG II experiment, and the $mu egamma$ dipole can be probed further by $mu to 3e$ and $mu N to eN$. With its promised sensitivity range and ability to use different nuclei, the $mu N to e N$ conversion experiments can not only make discovery, but access the extra diagonal quark Weinberg couplings $rho_{qq}$. For the $tau$ lepton, $tau to mugamma$ would probe $rho_{tautau}$ down to $lambda_tau$ or lower, while $tau to 3mu$ would probe $rho_{mumu}$ to ${cal O}(lambda_{mu})$.
We propose a SUSY scenario to explain the current electron and muon $g-2$ discrepancies without introducing lepton flavor mixings. Threshold corrections to the Yukawa couplings can enhance the electron $g-2$ and flip the sign of the SUSY contributions. The mechanism predicts a flavor-dependent slepton mass spectrum. We show that it is compatible with the Higgs mediation scenario.
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