MSSM Electroweak Baryogenesis and LHC Data

TL;DR

This paper evaluates MSSM electroweak baryogenesis in the presence of a light stop, noting that a 125 GeV Higgs mass requires a very heavy second stop and can clash with LHC Higgs data due to gluon-fusion enhancements. It shows that a light neutralino with mass below ~60 GeV can alleviate these tensions by enabling a sizable Higgs invisible width and by driving stop decays to three- or four-body final states, making the scenario compatible with current data and testable at the HL-LHC. The analysis combines collider constraints, Higgs/Z invisible widths, and dark matter considerations to delineate viable parameter regions, highlighting the dependence on μ, tanβ, and neutralino mixing. The work argues that precise measurements of Higgs channels and stop signatures at the HL-LHC will be decisive in confirming or ruling out this MSSM EWBG realization.

Abstract

Electroweak baryogenesis is an attractive scenario for the generation of the baryon asymmetry of the universe as its realization depends on the presence at the weak scale of new particles which may be searched for at high energy colliders. In the MSSM it may only be realized in the presence of light stops, and with moderate or small mixing between the left- and right-handed components. Consistency with the observed Higgs mass around 125 GeV demands the heavier stop mass to be much larger than the weak scale. Moreover the lighter stop leads to an increase of the gluon-gluon fusion Higgs production cross section which seems to be in contradiction with indications from current LHC data. We show that this tension may be considerably relaxed in the presence of a light neutralino with a mass lower than about 60 GeV, satisfying all present experimental constraints. In such a case the Higgs may have a significant invisible decay width and the stop decays through a three or four body decay channel, including a bottom quark and the lightest neutralino in the final state. All these properties make this scenario testable at a high luminosity LHC.

Figures (8)

• Figure 1: The window with $\langle\phi(T_n)\rangle/T_n\gtrsim 1$ for a gluino mass $M_3=700$ GeV, $m_Q \le 50\,$TeV (left panel) and $m_Q\le10^6$ TeV (right panel).
• Figure 2: Left panel: Allowed region in the $(M_1,\mu)$-plane, for $M_2=200$ GeV, from the constraint in Eq. (\ref{['invisible']}) for $\tan\beta =$ 15 [above the intermediate (red) solid line], 5 [above the upper (blue) solid line] and 2 [above the lower (black) solid line]. For comparison we also show the corresponding allowed regions (above the corresponding dashed lines) for $\tan\beta=15$ (lower line) to $\tan\beta=2$ (upper line) from bounds on the lightest chargino mass $m_{\chi^\pm_1}>94$ GeV. Right panel: The same in the $(\mu,\tan\beta)$-plane for $M_1=$20 GeV [upper (red) solid], 30 GeV [intermediate (blue) solid] and 40 GeV [lower (black) solid].
• Figure 3: $(\sigma\times$BR$)/(\sigma\times$BR$)_{\rm SM}$ of the Higgs (left panel) and BR of the Higgs (right panel, channels with BR$<0.1$ are omitted) as a function of $m_{\chi^0_1}$ at point B of Fig. \ref{['figure-1']} for $M_2=\mu=200\,$GeV. The Higgs mass is about 125 GeV. The lightest chargino and next-to-lightest neutralino (lower and upper dot-dashed lines in the right panel) are heavier than the light stop. The vertical dot-dot-dashed line corresponds to the Tevatron lower bound on the lightest neutralino assuming BR$(\tilde{t} \rightarrow c ~\chi^0_1)=1$. On the left (right) of the vertical dotted line the stop can decay as in Eq. (\ref{['bWchi']}) with a real (virtual) W boson.
• Figure 4: The same as Fig. \ref{['figure-4']} but for point G and $M_2=\mu=200$ GeV. The Higgs mass is about 125 GeV.
• Figure 5: Evolution along the path BG of Fig. \ref{['figure-1']} of $\sigma\times {\rm BR}/(\sigma\times {\rm BR})_{SM}$ (left panels) and BR (right panels) for $M_2=\mu=200$ GeV and $M_1=20$ GeV.