The MSSM confronts the precision electroweak data and the muon g-2

TL;DR

The paper confronts the MSSM with the latest muon $g-2$ results and precision EW data, showing that SUSY contributions can bridge the gap between the SM prediction and observation, particularly with sleptons in the few-hundred GeV range for $\tan\beta \lesssim 10$ or heavier sleptons (up to $\sim 1$ TeV) for $\tan\beta \approx 50$. It presents a detailed one-loop analysis of MSSM contributions to $a_{\mu}$, emphasizes the dominant diagrams, and maps parameter regions consistent with $\text{Br}(b\to s\gamma)$ and dark matter relic density. In the EW sector, oblique parameters $\Delta S_Z$, $\Delta T_Z$ and the $m_W$ prediction are used to quantify MSSM effects, finding modest improvements over the SM, sensitive to jet asymmetry data. The study also examines specific SUSY-breaking scenarios (mSUGRA, gauge mediation, and mirage mediation), identifying viable regions with light sleptons and inos that satisfy all constraints and remain testable at the LHC. Overall, the work demonstrates that MSSM remains a compatible and predictive framework for flavor, EW precision, and collider phenomenology in light of current data.

Abstract

We update the electroweak study of the predictions of the Minimal Supersymmetric Standard Model (MSSM) including the recent results on the muon anomalous magnetic moment, the weak boson masses, and the final precision data on the Z boson parameters from LEP and SLC. We find that the region of the parameter space where the slepton masses are a few hundred GeV is favored from the muon g-2 for \tanβ\ltsim 10, whereas for \tanβ\simeq 50 heavier slepton mass up to \sim 1000 GeV can account for the reported 3.2 σdifference between its experimental value and the Standard Model (SM) prediction. As for the electroweak measurements, the SM gives a good description, and the sfermions lighter than 200 GeV tend to make the fit worse. We find, however, that sleptons as light as 100 to 200 GeV are favored also from the electroweak data, if we leave out the jet asymmetry data that do not agree with the leptonic asymmetry data. We extend the survey of the preferred MSSM parameters by including the constraints from the b \to s γtransition, and find favorable scenarios in the minimal supergravity, gauge-, and mirage-mediation models of supersymmetry breaking.

Figures (12)

• Figure 1: The SUSY contributions to the muon $g-2$ which give the leading terms of the expansion in $m_Z/m_{\rm SUSY}$. The photon (wavy line) is attached to all the charged particles.
• Figure 2: The behaviors of the functions $F_a(x,y)$ and $F_b(x,y)$, which appear in SUSY contributions to the muon $g-2$, for $y=x, 2x, 3x$.
• Figure 3: The muon $g-2$, plotted against $M_2$ (the $SU(2)_L$ gaugino mass) and $m_{\tilde{E}}$ (the right-handed smuon soft SUSY breaking mass) for $\tan\beta=10$ (top two panels) and $\tan\beta=50$ (bottom two panels), and for $\mu=200$ GeV (left two panels) and $\mu=800$ GeV (right two panels). The curves are, from the lower left corner, $+3\sigma$, $+2\sigma$, $+1\sigma$, $-1\sigma$ and $-2\sigma$ contour for the difference $\delta a_\mu$ between the data and the SM prediction. The region on the left-hand side of the vertical dotted line is excluded by the chargino mass limit $m_{\tilde{\chi}_1^-}>103.5$ GeV LEPSUSYWG, and the region below the horizontal dotted line is ruled out by the stau mass limit $m_{\tilde{\tau}_1} >81.9$ GeV PDG10. The region below or in the left-hand side of the dash-dotted curve gives $\Delta \chi^2_{\rm EW}>0.5$ contribution to the electroweak observables, see Eq. (\ref{['eq:chisqEWSUSY_SzTzMw']}). The sample points discussed in the main text are marked by the crosses ($\times$). In the figures, we assume $A_\mu=0$, $m_{\tilde{L}}=m_{\tilde{E}}$ and $M_1/M_2 = (5/3) \tan^2 \theta_W$.
• Figure 4: The comparison of $\chi^2_{\rm min}$ of the electroweak observables as a function of the SM Higgs boson mass $m_{H_{\rm SM}}$ fitted by using our parametrization (solid line) and by using the output of ZFITTER (dashed line). Our parametrization is valid for $m_{H_{\rm SM}} > 100$ GeV.
• Figure 5: The squark, slepton and ino contributions to $(\Delta S_Z, \Delta T_Z)$ for $\tan\beta=10$. The SUSY breaking scalar masses for the left-handed and right-handed squarks are assumed to be same, denoted by $m_{\widetilde{Q}}$. The $\widetilde{t}_L$-$\widetilde{t}_R$ and $\widetilde{b}_L$-$\widetilde{b}_R$ mixings are controlled by $A_{\rm eff} = A_{\rm eff}^t = A_{\rm eff}^b$. The left- and right-handed sleptons are also assumed to have a common SUSY breaking scalar mass $m_{\widetilde{L}}$. The reference SM point, $(m_t^{}, m_{H_{\rm SM}}, \Delta \alpha_{\rm had}^{(5)}(m_Z^2))=(172 {\rm GeV}, 120 {\rm GeV}, 0.0277)$, is marked by the open circle at the origin of the plot. If a different value of $m_t^{}$ is chosen, then the origin would move according to the scale shown at the right-hand side. Similarly, if a different value of $\Delta \alpha_{\rm had}^{(5)}(m_Z^2)$ is chosen, the origin would move according to the scale shown at the bottom.