I. Saha | Searcharxiv

arXiv2025

GUT-based NMSSM with Singlino Dark Matter: Describing the ATLAS/CMS Excesses

One of the main goals of the ongoing LHC program is the search for BSM physics, with EW SUSY partners still allowed with masses as low as a few hundred GeV. Over the last years, searches for the ``golden channel'', $pp \to \tilde\chi^0_2 \tilde\chi^\pm_1 \to \tilde\chi^0_1 Z^{(*)} \, \tilde\chi^0_1 W^{\pm (*)}$ show consistent excesses between CMS and ATLAS in the 2 soft-lepton and 3 soft-lepton plus missing $E_T$ searches, favoring mass scales of $m_{\tilde\chi^0_2} \approx m_{\tilde\chi^{\pm}_1} \ge 200$ GeV and $\Delta m_{21} := m_{\tilde\chi^0_2} - m_{\tilde\chi^0_1} \approx 20$ GeV. We analyze these excesses in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We assume a singlino dominated lighest neutralino, $\tilde\chi^0_1$, as our Dark Matter (DM) candidate. The second and third lightest neutralinos, $\tilde\chi^0_{2,3}$ are higgsino like, with the higgsino mixing parameter $\mu$ being smaller than the soft SUSY-breaking bino and wino masses, $M_1$ and $M_2$. In particular, we assume the approximate GUT relations $M_1 \sim M_2/2 \sim M_3/6$, yielding a gluino mass $m_{\tilde g} \sim M_3 \ge 2$ TeV, in agreement with the LHC search limits. The scalar masses are assumed to heavy and do not play a role in our analysis. We demonstrate that this scenario is in agreement with all relevant experimental constraints, comprising the DM direct detection limits and the upper limit on the DM relic density, the LHC searches for SUSY particles and additional Higgs bosons, as well as the LHC Higgs-boson rate measurements. This constitutes the first explanation of the soft-lepton excesses in a model with GUT relations among the soft SUSY-breaking parameters.

hep-ph↗

arXiv2022

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

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, $(g-2)_μ$, and its Standard Model (SM) prediction. The new "MUON G-2" result, combined with the older BNL result on $(g-2)_μ$, yields a deviation from the SM prediction of $Δa_μ = (25.1 \pm 5.9) \times 10^{-10}$, corresponding to $4.2~σ$. 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 $(g-2)_μ$ 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 $1\,σ$ range of the experimental world average of $M_W^{\mathrm{exp}} = 80.379 \pm~0.012~\mathrm{GeV}$ 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 $\tildeχ^0_1$, accompanied by either a light chargino or a light smuon, setting interesting targets for future collider searches.

hep-ph↗