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

Abstract

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 .

Dark matter detectors as a novel probe for light new physics

“…Finally, it should be noted that upcoming experiments also have the potential to probe light mediator particles. However, our results provide about an order of magnitude more constrained bounds than those predicted for other future experiments such as neutrino trident interactions at DUNE [60], model dependent constraints for DARWIN [31] and constraints extracted from missing energy searches at NA64µ [31].…”

“…In addition to COHERENT, data-driven constraints also exist from upper limits on CEνNS, placed by the recent CONNIE [28] and CONUS [29] measurements. Phenomenological studies focusing on various U (1) realisations such as the L µ − L τ and B − L guage symmetries have been explored using solar neutrinos [30,31] as well as using supernova neutrinos taking also into account corrections from medium effects [32]. It is interesting to note that the latter can induce a reduction of the cross section due to Pauli blocking and therefore lead to less severe constraints.…”

On (g − 2)μ from gauged U(1)X

“…The U(1) Lµ−Lτ gauge symmetry forces the dimension-4 charged lepton Yukawa interactions to be diagonal, ensuring an accidental U(1) 3 lepton flavor symmetry. The L µ −L τ gauge boson X µ with mass m X ∈ [10,210] MeV and a coupling to muons in the range g X ∈ [0.4, 1] × 10 −3 gives a one-loop contribution to (g − 2) µ of the right size to account for the experimental anomaly while not conflicting with any of other measurements [52,[62][63][64][65].…”

Sleptonic SUSY: From UV Framework to IR Phenomenology

“…However, it is extremely difficult for such a Z to account for the muon g−2 discrepancy without being excluded by searches that relate the couplings to muons and electrons [32]. Non-universal Z 's can evade such search constraints, but are also severely constrained by various searches [32,85], and avoid lepton FCNCs, such as µ → e + X, by assigning the three generations different Z charges so that their Yukawa matrices and Z interactions are necessarily flavor-diagonal in the same basis (with neutrino masses/mixing arising as a small correction to this). But in the SM, the GIM mechanism remarkably protects against FCNCs even when there is no distinction between generations in the gauge assignments and the Yukawa matrices are a priori non-diagonal.…”