Light Stau Phenomenology and the Higgs γγRate

TL;DR

The paper investigates a MSSM-inspired light stau scenario with large mixing as a driver for an enhanced Higgs diphoton rate near 125 GeV. It analyzes how such light staus affect Higgs phenomenology, precision observables, dark matter, and high-energy RG running, and it outlines collider signatures at the LHC, emphasizing weak production channels like the associated production of a light stau and tau sneutrino. The study finds that a ~50% enhancement in h→γγ is feasible without spoiling other Higgs rates, and that DM can be accommodated via stau–neutralino co-annihilation; RG evolution points to a low messenger scale for flavor universality, while LHC prospects hinge on weak production channels with promising reach at 14 TeV. Collectively, the work links Higgs physics, dark matter, and collider phenomenology in a coherent framework for light sleptons in the MSSM.

Abstract

Recently, an excess of events consistent with a Higgs boson with mass of about 125 GeV was reported by the CMS and ATLAS experiments. This Higgs boson mass is consistent with the values that may be obtained in minimal supersymmetric extensions of the Standard Model (SM), with both stop masses less than a TeV and large mixing. The apparently enhanced photon production rate associated with this potential Higgs signal may be the result of light staus with large mixing. Large stau mixing and large coupling of the staus to the SM-like Higgs boson may be obtained for large values of tan β, and moderate to large values of the Higgsino mass parameter, μ. We study the phenomenological properties of this scenario, including precision electroweak data, the muon anomalous magnetic moment, Dark Matter, and the evolution of the soft supersymmetry-breaking parameters to high energies. We also analyze the possible collider signatures of light third generation sleptons and demonstrate that it is possible to find evidence of their production at the 8 TeV and the 14 TeV LHC. The most promising channel is stau and tau sneutrino associated production, with the sneutrino decaying into a W boson plus a light stau.

Figures (12)

• Figure 1: Contours of the stop mixing parameter, $A_t$, necessary for a Higgs mass $\sim$ 125 GeV given in the plane of the left- and right-handed stop soft supersymmetry-breaking mass parameters, $m_{Q_3}$, $m_{u_3}$ for $\mu = 650$ GeV, $m_A=1500$ GeV and $A_\tau=500$ GeV. Left:$\tan\beta = 10$. Right:$\tan\beta = 60$, which is where stau effects can be relevant for the diphoton production rate.
• Figure 2: Contour plots of the ratio of the $\sigma(gg \to h) \times$ BR($h \to VV$) to its SM value, in the (a) & (c):$\mu$--$m_{L_3}$ plane with $m_{e_3}=m_{L_3}$, and (b) & (d):$m_{e_3}$--$m_{L_3}$ plane with $\mu =650$ GeV. $\tan\beta = 60$, $m_A=1$ TeV and $A_\tau=0$ GeV are kept fixed for all the plots. The relevant squark parameters are $A_t=1.4$ TeV and $m_{Q_3}=m_{u_3}=850$ GeV giving $m_h\sim 125$ GeV. Red dashed lines are contours of lightest stau masses. The yellow shaded area denotes the region satisfying the LEP bound on the lightest stau mass. Enhanced branching ratios are obtained for values of $\mu$ for which the lightest stau mass is close to its experimental limit, of about (85-90) GeV.
• Figure 3: Contour plots of the ratio of BR($h \to b\bar{b}$) to its SM value, in the $m_A$--$A_\tau$ plane with $\tan\beta = 60$, $m_{e_3}=m_{L_3}=250$ GeV. We fix $m_{\tilde{\tau}_1}=90$ GeV, hence $\mu$ varies in the range 500--550 GeV. The relevant squark parameters are $A_t=1.8$ TeV and $m_{Q_3}=m_{u_3}=1.5$ TeV corresponding to $m_{\tilde{t}_{1,2}}\sim 1.4, 1.6$ TeV and $m_{h}\sim$ 125 GeV.
• Figure 4: Ratio of the $\sigma(gg \to h) \times$ BR($h \to VV$) to its SM value, for both $V=\gamma$ and $V=Z$ as a function of $m_{e_3}=m_{L_3}$, for $\tan \beta=60$ varying $\mu$ such that $m_{\tilde{\tau}_1}=90$ GeV for different values of $A_\tau$. The Higgs mass varies with $m_{e_3}$, but remains $\sim125$ GeV. (a): $m_A = 1.5$ TeV, $A_t = 2$ TeV, $m_{Q_3} =2.5$ TeV, $m_{u_3} = 100$ GeV leading to $m_{\tilde{t}_1}\sim140$ GeV. (b): $m_A =1$ TeV, $A_t = 1.4$ TeV, $m_{Q_3} =1.5$ TeV, $m_{u_3} = 500$ GeV leading to $m_{\tilde{t}_1}\sim500$ GeV.
• Figure 5: Contour plots of $m_W$ Light blue fill denotes regions experimentally consistent within 1-$\sigma$ for the $W$ mass ($80.385\pm0.015$ GeV), with darker blue contours specifying the values of $m_W$. Light green fill denotes allowed region for the lightest stau mass ($m_{\tilde{\tau}} > 90$ GeV), with red lines denoting contours of the stau mass. In the right panel, we present results for $\mu = 650$ GeV and $\tan\beta = 60$, while in the left panel $\tan\beta = 60$ and $m_{L_3} = m_{e_3}$. All the other soft parameters are fixed to 2 TeV