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Register a new userEffect of Systematic Uncertainty Estimation on the Muon $g-2$ Anomaly
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Glen Cowan
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The statistical significance that characterizes a discrepancy between a measurement and theoretical prediction is usually calculated assuming that the statistical and systematic uncertainties are known. Many types of systematic uncertainties are, however, estimated on the basis of approximate procedures and thus the values of the assigned errors are themselves uncertain. Here the impact of the uncertainty {it on the assigned uncertainty} is investigated in the context of the muon $g-2$ anomaly. The significance of the observed discrepancy between the Standard Model prediction of the muons anomalous magnetic moment and measured values are shown to decrease substantially if the relative uncertainty in the uncertainty assigned to the Standard Model prediction exceeds around 30%. The reduction in sensitivity increases for higher significance, so that establishing a $5sigma$ effect will require not only small uncertainties but the uncertainties themselves must be estimated accurately to correspond to one standard deviation.
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The long-standing muon $g-2$ anomaly has been confirmed recently at the Fermilab. The combined discrepancy from Fermilab and Brookhaven results shows a difference from the theory at a significance of 4.2 $sigma$. In addition, the LHC has updated the lower mass bound of a pure wino. In this letter, we study to what extent the $g-2$ can be explained in anomaly mediation scenarios, where the pure wino is the dominant dark matter component. To this end, we derive some model-independent constraints on the particle spectra and $g-2$. We find that the $g-2$ explanation at the 1$sigma$ level is driven into a corner if the higgsino threshold correction is suppressed. On the contrary, if the threshold correction is sizable, the $g-2$ can be explained. In the whole viable parameter region, the gluino mass is at most $2-4,$TeV, the bino mass is at most $2,$TeV, and the wino dark matter mass is at most $1-2,$TeV. If the muon $g-2$ anomaly is explained in the anomaly mediation scenarios, colliders and indirect search for the dark matter may find further pieces of evidence in the near future. Possible UV models for the large threshold corrections are discussed.
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 $m_{tilde{mu}_{rm L}}gtrsim m_{tilde{chi}^{pm}_1}$ are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low $tan beta$ with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with $m_{tilde{mu}}lesssim 230$ 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 $m_{tilde{mu}}lesssim 1.3$ TeV.
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. We analyze the collider tests of this framework and find that the HL-LHC can probe the entire parameter space of these models.
The new measurement of the anomalous magnetic momentum of muon at the Fermilab Muon $g-2$ experiment has strengthened the significance of the discrepancy between the standard model prediction and the experimental observation from the BNL measurement. If new physics responsible for the muon $g-2$ anomaly is supersymmetric, one should consider how to obtain light electroweakinos and sleptons in a systematic way. The gauge coupling unification allows a robust prediction of the gaugino masses, indicating that the electroweakinos can be much lighter than the gluino if anomaly-mediated supersymmetry breaking is sizable. As naturally leading to mixed modulus-anomaly mediation, the KKLT scenario is of particular interest and is found capable of explaining the muon $g-2$ anomaly in the parameter region where the lightest ordinary supersymmetric particle is a bino-like neutralino or slepton.
We construct models with minimal field content that can simultaneously explain the muon g-2 anomaly and give the correct dark matter relic abundance. These models fall into two general classes, whether or not the new fields couple to the Higgs. For the general structure of models without new Higgs couplings, we provide analytical expressions that only depend on the $SU(2)_L$ representation. These results allow to demonstrate that only few models in this class can simultaneously explain $(g-2)_mu$ and account for the relic abundance. The experimental constraints and perturbativity considerations exclude all such models, apart from a few fine-tuned regions in the parameter space, with new states in the few 100 GeV range. In the models with new Higgs couplings, the new states can be parametrically heavier by a factor $sqrt{1/y_mu}$, with $y_mu$ the muon Yukawa coupling, resulting in masses for the new states in the TeV regime. At present these models are not well constrained experimentally, which we illustrate on two representative examples.
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