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Muon and electron g − 2 and lepton masses in flavor models

Lorenzo Calibbi, M. L. López-Ibáñez, Aurora Melis, Oscar Vives
2020 Journal of High Energy Physics  
The stringent experimental bound on µ → eγ is compatible with a simultaneous and sizable new physics contribution to the electron and muon anomalous magnetic moments (g − 2) ( = e, µ), 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) 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
more » ... ibution to the anomalous magnetic moment. In this framework, we introduce a chiral enhancement from a non-trivial 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 χ ∈ [0.6, 2.5] TeV. Despite the lack of direct signals for new physics from the high-energy collision data collected by the LHC experiments, we have a number of solid arguments, both theoretical and observational, that call for extensions of the Standard Model (SM). The most convincing of those -related to the origin of neutrino masses, dark matter, baryon asymmetry etc. -do not necessarily point to new particles at scales accessible at colliders in the foreseeable future. However, recent years have been also witnessing the arising of several hints for non-standard phenomena from precision observables involving lepton flavors. Signs of departure from the universality of leptonic couplings predicted by the SM in semi-leptonic decays of B mesons have been reported by LHCb and B-factories experiments both in neutral-and charged-current processes -for recent reviews see [1] [2] [3] . If confirmed by future data, these discrepancies would certainly require low-scale new physics coupling with different strength to different lepton families. Another discrepancy that would point to an analogous conclusion is related to the anomalous magnetic moment of the muon, (g − 2) µ . The experimental measurements of (g−2) µ have been in tension with the increasingly accurate theoretical calculations within the SM for about 20 years. The discrepancy currently amounts to about 3.5 σ [4-10]. 1 The situation may be clarified -and the case for new physics possibly reinforced -by the upcoming results of the new Muon g-2 experiment at FNAL [14] . It is well known that new particles coupling to muons can easily account for the (g − 2) µ provided that their mass are few TeV at most -for a recent review see [15] . 1 See, however, the very recent lattice result of the leading order hadronic vacuum polarization [11] , which, contrary to previous results, could reduce this discrepancy. On the other hand, even if the anomaly is accounted for by the hadronic vacuum polarization, this would reflect in a deterioration of the EW fit and the arising of tensions of comparable significance in other observables [12, 13] .
doi:10.1007/jhep06(2020)087 fatcat:4jjcgidvrvb6nbi6yfiw44anka