Interdependence of the new "MUON G-2" Result and the $W$-Boson Mass

Abstract

The electroweak (EW) sector of the Minimal Supersymmetric extension of the Standard Model (MSSM), assuming the lightest neutralino as Dark Matter (DM) candidate, can account for a variety of experimental results. In particular it can account for the discrepancy between the experimental result for the anomalous magnetic moment of the muon, $(g-2{)}_{\mu }$, and its Standard Model (SM) prediction. The new "MUON G-2" result, combined with the older BNL result on $(g-2{)}_{\mu }$, yields a deviation from the SM prediction of $\Delta a_{\mu }=(25.1\pm 5.9)\times 10^{-10}$, corresponding to $4.2\sigma$. Using this updated bound, together with the other constraints, we calculate the MSSM prediction for the mass of the $W$ boson, $M_W$. We assume contributions only from the EW sector, with the colored sector of the MSSM taken to be heavy. We investigate five scenarios, distinguished by the mechanisms which yield a relic DM density in agreement with the latest Planck bounds. We find that with the new $(g-2{)}_{\mu }$ result taken into account and depending on the scenario, values up to $M_W^{\mathrm{MSSM}}\lesssim 80.376\mathrm{GeV}$ are reached. The largest values are obtained for wino DM and in the case of slepton co-annihilation, where points well within the $1\sigma$ range of the experimental world average of $M_W^{\exp }=80.379\pm 0.012\mathrm{GeV}$ are reached, whereas the SM predicts a too small value of $M_W^{\mathrm{SM}}=80.353\mathrm{GeV}$. We analyze the dependence of $M_W^{\mathrm{MSSM}}$ on the relevant masses of the EW superpartners and demonstrate that future $M_W$ measurements, e.g. at the ILC, could distinguish between various MSSM realizations. Sizable contributions to $M_W^{\mathrm{MSSM}}$ are associated with a relatively light ${\tilde{\chi }}_1^0$, accompanied by either a light chargino or a light smuon, setting interesting targets for future collider searches.

Comments: 26 pages, 7 figures; v2: slight modification to text and note added in relation to the recent CDF MW measurement