Impact of quark flavor violating SUSY on h(125) decays at future lepton colliders

TL;DR

The paper investigates whether the 125 GeV SM-like Higgs can be the MSSM lightest CP-even Higgs $h^0$ under general quark flavor violation (QFV) driven by squark mixing. It computes $\Gamma(h^0\to c\bar{c}, b\bar{b}, b\bar{s})$ at full one-loop and $\Gamma(h^0\to g g, \gamma\gamma)$ at NLO QCD within the MSSM with general QFV, then performs a comprehensive parameter scan under updated theoretical and experimental constraints, including HL-LHC expectations. The results show potentially large, correlated deviations from SM predictions (e.g., $\text{DEV}(c)$ up to $\pm60\%$, $\text{DEV}(b)$ up to $\pm20\%$, and $\text{DEV}(b/c)$ exceeding $+100\%$) driven by strong scharm-stop and sstrange-sbottom mixing and sizeable trilinear couplings, with additional sizable QFV in $B(h^0\to b\,s)$. These effects remain accessible at future lepton colliders (ILC, CLIC, CEPC, FCC-ee, Muon Collider) even if HL-LHC does not discover SUSY, making observation of these patterns a strong indicator of QFV SUSY. The study also highlights the utility of width ratios, which suppress uncertainties and enhance sensitivity to virtual SUSY loops, and provides a benchmark scenario (P1) illustrating the parameter dependence and mass spectra consistent with current constraints.

Abstract

We study the CP-even neutral Higgs boson decays $h^0 \to c \bar{c}, b \bar{b}, b \bar{s}, γγ, g g$ in the Minimal Supersymmetric Standard Model (MSSM) with general quark flavor violation (QFV) due to squark generation mixings, identifying the $h^0$ as the Higgs boson with a mass of 125 GeV. We compute the widths of the $h^0$ decays to $c \bar c, b \bar b, b \bar s$ at full one-loop level. For the $h^0$ decays to $γγ$ and $g g$ we compute the widths at NLO QCD level. {\it For the first time}, we perform a systematic MSSM parameter scan for these widths respecting all the relevant theoretical and experimental constraints, such as those from B-meson data, and the 125 GeV Higgs boson data from recent LHC experiments, as well as the limits on Supersymmetric (SUSY) particle (sparticle) masses from the LHC experiments. We also take into account the expected sparticle mass limits from the future HL-LHC experiment in our analysis. {\it In strong contrast to} the usual studies in the MSSM with Minimal Flavor Violation (MFV), we find that the deviations of these MSSM decay widths from the Standard Model (SM) values can be quite sizable and that there are significant correlations among these deviations. All of these sizable deviations in the $h^0$ decays are mainly due to large scharm-stop mixing and large sstrange-sbottom mixing. Such sizable deviations from the SM can be observed at high signal significance in future lepton colliders such as ILC, CLIC, CEPC, FCC-ee and muon collider {\it even after} the failure of SUSY particle discovery at the HL-LHC. In case the deviation pattern shown here is really observed at the lepton colliders, then it would strongly suggest the discovery of QFV SUSY (the MSSM with general QFV).

Figures (12)

• Figure 1: (a) The $\tilde{u}_i$-$\tilde{g}$ loop corrections to $\Gamma(h^0 \to c \bar{c})$, (b) the $\tilde{u}_i$-$\tilde{\chi}^\pm_{1,2}$ loop and (c) the $\tilde{d}_i$-$\tilde{g}$ loop corrections to $\Gamma(h^0 \to b \, \, \bar{b} / \bar{s})$.
• Figure 2: (a) The SM (X = top quark) and MSSM (X = $\tilde{u}_{1,2,3}$) loop contributions to $\Gamma(h^0 \to g g)$, and (b) the SM (X = $W^+$ boson, top quark) and MSSM (X = $\tilde{u}_{1,2,3}$) loop contributions to $\Gamma(h^0 \to \gamma \gamma)$. The NLO QCD correction diagrams are not shown in these figures. For (a) $h^0 \to g g$, the MSSM ($\tilde{u}_{i}$) loop diagrams with the contact interactions of $\tilde{u}_{i}$-$\tilde{u}_{i}$-gluon-gluon are not shown. For (b) $h^0 \to \gamma \gamma$, the SM ($W^+$) loop diagram with that of W-W-$\gamma$-$\gamma$ and the MSSM ($\tilde{u}_{i}$) loop diagrams with those of $\tilde{u}_{i}$-$\tilde{u}_{i}$-$\gamma$-$\gamma$ are not shown.
• Figure 3: Shown in (a) is the scatter plot in the DEV(c)-DEV(b) plane obtained from the MSSM parameter scan described in Section \ref{['sec:full scan']}. "X" marks the SM point. The green and blue boxes indicate the expected $1\sigma$ errors at ILC250 and ILC250+500, respectively (see Table \ref{['table_DEVerror_LC']}). Though in principle the expected $1\sigma$ error should be shown by an error ellipse, here it is shown by an error box as an approximation since such $1\sigma$ error ellipse in the $\kappa_c$-$\kappa_b$ plane (and hence, in the DEV(c)-DEV(b) plane) is not given in ESU2020_RepSnowmass2021_Rep. The expected absolute $1\sigma$ errors at the other lepton colliders are similar to those at ILC (see Table \ref{['table_DEVerror_LC']}). In (b) we show also the ATLAS and CMS data of DEV(b) obtained from the recent $\kappa_b$ data kappa_bgamg_ATLASkappa_bgamg_CMS by using the DEV(b)-$\kappa_b$ relation DEV(b) = $\kappa_b^2$ - 1.
• Figure 4: The scatter plot in the (a) $\textnormal{DEV}(c)$-$\textnormal{DEV}(b/c)$ and (b) $\textnormal{DEV}(b)$-$\textnormal{DEV}(b/c)$ planes obtained from the MSSM parameter scan described in Section \ref{['sec:full scan']}. "X" marks the SM point. The expected absolute $1\sigma$ errors at ILC250 shown by the green box are given by ($\Delta \textnormal{DEV}(c)$, $\Delta \textnormal{DEV}(b)$, $\Delta \textnormal{DEV}(b/c)$)=(3.6%, 1.7%, 3.1%) (see Table \ref{['table_DEVerror_LC']}). Though, in principle, the expected $1\sigma$ error should be shown by an error ellipse, here it is shown by an error box as an approximation. The expected absolute $1\sigma$ errors at the other lepton colliders are similar to those at ILC (see Table \ref{['table_DEVerror_LC']}).
• Figure 5: The scatter plot in the $B(h^0 \to b s)$-$\textnormal{DEV}(b)$ plane obtained from the MSSM parameter scan described in Section \ref{['sec:full scan']}. The blue horizontal line indicates the ILC250+500+1000 sensitivity to $B(h^0 \to b s)$ of $\sim$0.1% at 4$\sigma$ signal significance. "X" marks to the SM point.