Higgs Boson Signatures of MSSM Electroweak Baryogenesis

TL;DR

The paper investigates MSSM electroweak baryogenesis, which requires a light, mostly right-handed stop and a SM-like light Higgs, and analyzes how this light stop alters Higgs signatures. Using an effective theory with heavy states integrated out, it shows that the Higgs production rate via gluon fusion is significantly enhanced while the diphoton decay rate is suppressed, due to constructive interference in $gg\to h^0$ and destructive interference in $h^0\to \gamma\gamma$, with the two effects tied to the Higgs-stop coupling $Q$ that also drives the first-order phase transition. The inclusive Higgs production rate $pp\to h^0\to \gamma\gamma$ is increased by about $1.4$–$1.6$× in the allowed EWBG region, with larger enhancements in gluon-fusion–dominated channels and reductions in VBF/associated production. The authors argue these modified Higgs signatures are testable at the LHC (and potentially the Tevatron) and provide a direct probe of the strength of the electroweak phase transition in MSSM EWBG, linking cosmology to collider phenomenology through the light stop.

Abstract

Electroweak baryogenesis (EWBG) in the MSSM can account for the cosmological baryon asymmetry, but only within a restricted region of the parameter space. In particular, MSSM EWBG requires a mostly right-handed stop that is lighter than the top quark and a standard model-like light Higgs boson. In the present work we investigate the effects of the light stop on Higgs boson production and decay. Relative to the standard model Higgs boson, we find a large enhancement of the Higgs production rate through gluon fusion and a suppression of the Higgs branching fraction into photon pairs. These modifications in the properties of the Higgs boson are directly related to the effect of the light stop on the electroweak phase transition, and are large enough that they can potentially be tested at the Tevatron and the LHC.

Figures (6)

• Figure 1: Value of the low-energy Higgs-stop coupling $Q$ computed at tree-level, and using the light stop effective theory. The relevant model parameter values are taken to be $m_{U_3}^2 = -(80 \,\, {\rm GeV})^2$, $\tan\beta = 10$, and $M = m_{Q_3} = 10,\,1000\,\, {\rm TeV}$.
• Figure 2: Higgs boson decay width to gluons $\Gamma(h^0\to gg)$ relative to the SM as a function of $m_{h^0}$ and $m_{\tilde{t}_1}$ for ${M} = 10,\,1000\,\, {\rm TeV}$ and $\tan\beta = 5,\,15$.
• Figure 3: Higgs boson branching fraction to diphotons $BR(h^0\to \gamma\gamma)$ relative to the SM as a function of $m_{h^0}$ and $m_{\tilde{t}_1}$ for ${M} = 10,\,1000\,\, {\rm TeV}$ and $\tan\beta = 5,\,15$.
• Figure 4: Inclusive $pp\to h^0\to \gamma\gamma$ production rate at the LHC relative to the SM as a function of $m_{h^0}$ and $m_{\tilde{t}_1}$ for ${M} = 10,\,1000\,\, {\rm TeV}$ and $\tan\beta = 5,\,15$.
• Figure 5: Higgs boson masses as a function of $m_{U_3}$ and $|X_t|/M$ for $\tan\beta = 5,\,15$ and $M = 10,\,1000\,\, {\rm TeV}$.