The tiny (g-2) muon wobble from small-μ supersymmetry

A new measurement of the muon anomalous magnetic moment, gμ− 2, has been reported by the Fermilab Muon g-2 collaboration and shows a 4.2 σ 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 concentrate on a simple supersymmetric model that also provides a dark matter explanation in a previously unexplored region of supersymmetric parameter space. Such interesting region can realize a Bino-like dark matter candidate compatible with all current direct detection constraints for small to moderate values of the Higgsino mass parameter |μ|. This in turn would imply the existence of light additional Higgs bosons and Higgsino particles within reach of the high-luminosity LHC and future colliders. We provide benchmark scenarios that will be tested in the next generation of direct dark matter experiments and at the LHC.

NNLO virtual and real leptonic corrections to muon-electron scattering

The recently proposed MUonE experiment at CERN aims at providing a novel determination of the leading order hadronic contribution to the muon anomalous magnetic moment through the study of elastic muon-electron scattering at relatively small momentum transfer. The anticipated accuracy of the order of 10ppm demands for high-precision predictions, including all the relevant radiative corrections. The fixed-order NNLO radiative corrections due to the emission of virtual and real leptonic pairs are described and their numerical impact is discussed for typical event selections of the MUonE experiment, by means of the upgraded Monte Carlo code Mesmer.

Confirming $$U(1)_{L_\mu -L_{\tau }}$$ as a solution for $$(g-2)_\mu $$ with neutrinos

The recent measurement of the muon anomalous magnetic moment by the Fermilab E989 experiment, when combined with the previous result at BNL, has confirmed the tension with the SM prediction at $$4.2\,\sigma $$ 4.2 σ CL, strengthening the motivation for new physics in the leptonic sector. Among the different particle physics models that could account for such an excess, a gauged $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ stands out for its simplicity. In this article, we explore how the combination of data from different future probes can help identify the nature of the new physics behind the muon anomalous magnetic moment. In particular, we contrast $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ with an effective $$U(1)_{L_\mu }$$ U ( 1 ) L μ -type model. We first show that muon fixed target experiments (such as NA64$$\mu $$ μ ) will be able to measure the coupling of the hidden photon to the muon sector in the region compatible with $$(g-2)_\mu $$ ( g - 2 ) μ , and will have some sensitivity to the hidden photon’s mass. We then study how experiments looking for coherent elastic neutrino-nucleus scattering (CE$$\nu $$ ν NS) at spallation sources will provide crucial additional information on the kinetic mixing of the hidden photon. When combined with NA64$$\mu $$ μ results, the exclusion limits (or reconstructed regions) of future CE$$\nu $$ ν NS detectors will also allow for a better measurement of the mediator mass. Finally, the observation of nuclear recoils from solar neutrinos in dark matter direct detection experiments will provide unique information about the coupling of the hidden photon to the tau sector. The signal expected for $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ is larger than for $$U(1)_{L_\mu }$$ U ( 1 ) L μ with the same kinetic mixing, and future multi-ton liquid xenon proposals (such as DARWIN) have the potential to confirm the former over the latter. We determine the necessary exposure and energy threshold for a potential $$5\,\sigma $$ 5 σ discovery of a $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ boson, and we conclude that the future DARWIN observatory will be able to carry out this measurement if the experimental threshold is lowered to $$1\,{\mathrm {keV}}_{\mathrm {nr}} $$ 1 keV nr .

Muon g − 2 anomaly and neutrino magnetic moments

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. In contrast to other multi-scalar theories, in the model presented here there is no freedom to control the sign and strength of the muon g − 2 contribution. We analyze the collider tests of this framework and find that the HL-LHC can probe the entire parameter space of these models.

Probing the dark axion portal with muon anomalous magnetic moment

We propose a new scenario of using the dark axion portal at one-loop level to explain the recently observed muon anomalous magnetic moment by the Fermilab Muon g-2 experiment. Both axion/axion-like particle (ALP) and dark photon are involved in the same vertex with photon. Although ALP or dark photon alone cannot explain muon $$g-2$$ g - 2 , since the former provides only negative contribution while the latter has very much constrained parameter space, dark axion portal can save the situation and significantly extend the allowed parameter space. The observed muon anomalous magnetic moment provides a robust probe of the dark axion portal scenario.

Muon anomalous magnetic moment and Higgs potential stability in the 331 model from SU(6)

We consider a $$SU(3)_c \times SU(3)_L \times U(1)_X$$ S U ( 3 ) c × S U ( 3 ) L × U ( 1 ) X model from a SU(6) Grand Unified Theory (GUT). In order to explain the anomalous magnetic moments of muon and electron, we introduce two new scalar triplets without vacuum expectation values (VEVs) so that the leading contributions to $$\Delta a_{\mu }$$ Δ a μ and $$\Delta a_{e}$$ Δ a e can avoid the suppression from small muon mass. In addition, the Higgs potential stability of this 331 model is studied by giving a set of sufficient conditions to ensure the boundedness from below of the potential.

Supersymmetric interpretation of the muon g – 2 anomaly

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 $$ {m}_{{\tilde{\mu}}_{\mathrm{L}}}\gtrsim {m}_{{\tilde{\chi}}_1^{\pm }} $$ m μ ˜ L ≳ m χ ˜ 1 ± are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low tan β with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with $$ {m}_{\tilde{\mu}} $$ m μ ˜ ≲ 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 $$ {m}_{\tilde{\mu}} $$ m μ ˜ ≲ 1.3 TeV.