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Register a new userCombined explanations of $(g-2)_{mu,e}$ and implications for a large muon EDM
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With the long-standing tension between experiment and Standard-Model (SM) prediction in the anomalous magnetic moment of the muon, $a_mu=(g-2)_mu/2$, at the level of 3-4$sigma$, it is natural to ask if there could be a sizable effect in the electric dipole moment (EDM) $d_mu$ as well. In this context it has often been argued that in UV complete models the electron EDM, which is very precisely measured, excludes a large effect in $d_mu$. However, the recently observed 2.5$sigma$ tension in $a_e=(g-2)_e/2$, if confirmed, requires that the muon and electron sectors effectively decouple to avoid constraints from $muto egamma$. We briefly discuss UV complete models that possess such a decoupling, which can be enforced by an Abelian flavor symmetry $L_mu-L_tau$. We show that, in such scenarios, there is no reason to expect a correlation between the electron and muon EDM, so that the latter can be sizable. New limits on $d_mu$ improved by up to two orders of magnitude are expected from the upcoming $(g-2)_mu$ experiments at Fermilab and J-PARC. Beyond, a proposed dedicated muon EDM experiment at PSI could further advance the limit. In this way, future improved measurements of $a_e$, $a_mu$, as well as the fine-structure constant $alpha$ are not only set to provide exciting precision tests of the SM, but, in combination with EDMs, to reveal crucial insights into the flavor structure of physics beyond the SM.
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The minimal supersymmetric standard model (MSSM) with complex parameters can contribute sizably to muon/electron anomalous magnetic dipole momemnt ($g-2$) and electric dipole moment (EDM). The electron $g-2$ interplays with electron EDM; the muon $g-2$ can also interplay with electron EDM assuming the universality between smuon and selectron masses, either of which can constrain the relevant CP-phases in the MSSM. In this work, we first use such an interplay to derive an approximate analytical upper limit on the relevant CP-phase. Then we extensively scan the parameter space to obtain more accurate upper limits. We obtain the following observations: (i) The muon $g-2$ in the $2sigma$ range combined with the electron EDM upper limit (assuming the universality between smuon and selectron masses) typically constrains the relevant CP-phase under $1.9times 10^{-5} (text{rad})$; (ii) The electron $g-2$ in the $2sigma$ range (Berkeley) interplays with the electron EDM upper limit (without assuming the universality between smuon and selectron masses) constrains the relevant CP-phase under $3.9times 10^{-6}(text{rad})$ (also requiring muon $g-2$ in the allowed $2sigma$ range). We also find some special cancellations in the parameter space which can relax the constraints by a couple of orders. Such stringent limits on CP-phases may pose a challenge for model building of SUSY, i.e., how to naturally suppress these phases.
A new measurement of the muon anomalous magnetic moment has been recently reported by the Fermilab Muon g-2 collaboration and shows a $4.2,sigma$ departure from the most precise and reliable calculation of this quantity in the Standard Model. Assuming that this discrepancy is due to new physics, we consider its relation with other potential anomalies, especially in the muon sector, as well as clues from the early universe. We comment on new physics solutions discussed extensively in the literature in the past decades, to finally concentrate on a simple supersymmetric model that also provides a dark matter explanation. We show results for an interesting region of supersymmetric parameter space that can be probed at the high luminosity LHC and future colliders, while leading to values of ($g_mu-2$) consistent with the Fermilab and Brookhaven ($g_mu-2$) measurements. Such a parameter region can simultaneously realize a Bino-like dark matter candidate compatible with direct detection constraints for small to moderate values of the Higgsino mass parameter $|mu|$.
We discuss the recent results on the muon anomalous magnetic moment in the context of new physics models with light scalars. We propose a model in which the one-loop contributions to g-2 of a scalar and a pseudoscalar naturally cancel in the massless limit due to the symmetry structure of the model. This model allows to interpolate between two possible interpretations. In the first interpretation, the results provide a strong evidence of the existence of new physics, dominated by the positive contribution of a CP-even scalar. In the second one, supported by the recent lattice result, the data provides a strong upper bound on new physics, specifically in the case of (negative) pseudoscalar contributions. We emphasize that tree-level signatures of the new degrees of freedom of the model are enhanced relative to conventional explanations of the discrepancy. As a result, this model can be tested in the near future with accelerator-based experiments and possibly also at the precision frontier.
The deviation of the measured value of the muon anomalous magnetic moment from the standard model prediction can be completely explained by mixing of the muon with extra vectorlike leptons, L and E, near the electroweak scale. This mixing simultaneously contributes to the muon mass. We show that the correlation between contributions to the muon mass and muon g-2 is controlled by the mass of the neutrino originating from the doublet L. Positive correlation, simultaneously explaining both measured values, requires this mass below 200 GeV. The decay rate of the Higgs boson to muon pairs is modified and, in the region of the parameter space that can explain the muon anomalous magnetic moment within one standard deviation, it ranges from 0.5 to 24 times the standard model prediction. In the same scenario, $h to gamma gamma$ can be enhanced or lowered by ~50% from the standard model prediction. The explanation of the muon g-2 anomaly and predictions for $h to gamma gamma$ are not correlated since these are controlled by independent parameters. This scenario can be embedded in a model with three complete vectorlike families featuring gauge coupling unification, sufficiently stable proton, and the Higgs quartic coupling remaining positive all the way to the grand unification scale.
Numerous channels of the cross section e+e- --> hadrons have been measured by the BABAR experiment using the ISR method. For the pi+pi-(gamma) and K+K-(gamma) channels, BABAR has pioneered the method based on the ratio between the hadronic mass spectra and mu+mu-(gamma). Many systematic uncertainties cancel in the ratio, hence the precise measured cross sections. These measurements have been exploited for phenomenological studies, like the determination of the hadronic contribution to the anomalous magnetic moment of the muon (g-2)_mu.
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