Observing the Dark Scalar Doublet and its Impact on the Standard-Model Higgs Boson at Colliders

TL;DR

Observing the Dark Scalar Doublet and its Impact on the Standard-Model Higgs Boson at Colliders investigates a $Z_{2}$-odd inert scalar doublet, yielding the dark scalar sector with $H^{\pm}, H^{0}, A^{0}$ and rich interactions with the SM Higgs. The authors derive the scalar potential and mass relations, analyze LEP constraints on the dark sector, and compute how Higgs decays to dark scalars modify Higgs phenomenology, including potentially dominant invisible decays for $m_h$ in the 100–160 GeV range. They perform LHC studies showing that dark scalars can be produced via Drell–Yan processes, with the $h\to H^{0}H^{0}$ channel suppressing SM decays and making invisible Higgs searches via weak-boson fusion viable, while the $A^{0}H^{0}$ signature offers a complementary discovery mode. Overall, the DSDM can relax the traditional Higgs mass bounds and yield distinctive collider signals, underscoring the importance of considering dark-sector scalars in Higgs-boson analyses at current and future colliders.

Abstract

If the Standard Model of particle interactions is extended to include a second scalar doublet $[H^{+},(H^{0}+iA^{0})/\sqrt{2}]$, which is odd under an unbroken Z_{2} discrete symmetry, it may be called the $dark$ scalar doublet, because its lightest neutral member, say H^{0}, is one posssible component for the dark matter of the Universe. We discuss the general phenomenology of the four particles of this doublet, without assuming that H^{0} is the dominant source of dark matter. We also consider the impact of this $dark$ scalar doublet on the phenomenology of the SM Higgs boson h.

Figures (10)

• Figure 1: (left) The $95\%$ C.L. upper limit on $BR\left(h\to invisible\right)$, adapted from LEPII:2001xz; (right) The $95\%$ C.L. upper limit on $BR(h\to b\bar{b})$, adapted from Barate:2003sz. The label H in these figures refers to the SM Higgs boson $h$, and $\xi^{2}$ in the right figure is defined as $\xi^{2}\equiv\left(g_{HZZ}/g_{HZZ}^{SM}\right)^{2}$ (see Ref. Barate:2003sz for details).
• Figure 2: (a) Allowed parameter space (gray region) of $(m_{h},\lambda_{2})$; (b)(c) allowed parameter space of $\left(m_{H^{0}},\mu_{2}\right)$ after imposing the LEP II constraints on the decay branching ratio of $h\to{\rm invisible}$ and $h\to b\bar{b}$. The region above the dashed line is excluded by the vacuum stability requirement. From top to bottom: $\lambda_{2}=1.0,\,0.5,0.3,\,0.1$and $\lambda_{2}\to0$.
• Figure 3: (a) Selected Higgs boson decay branching ratios as a function of $m_{h}$ in the SM; (b) selected SM Higgs boson decaying ratios as a function of $m_{h}$ in the DSDM. Here we have chosen $m_{H^{0}}=50\,{\rm GeV}$, $\Delta m_{A^{0}H^{0}}=10\,{\rm GeV}$, $m_{H^{\pm}}=170\,{\rm GeV}$ and $\mu_{2}=20\,{\rm GeV}$. The vertical axis is units of GeV for the total decay width.
• Figure 4: (a) Total decay width of the SM Higgs boson as a function of $m_{h}$; (b) ratio of the total decay width of the SM Higgs boson in the DSDM and Higgs boson in the SM; (c) decay branching ratio of the invisible decay mode of the SM Higgs boson in the DSDM. For comparison, we choose $m_{H^{0}}=40\,\left(50,\,60\right)\,{\rm GeV}$, $\Delta m_{A^{0}H^{0}}=10\,{\rm GeV}$, $m_{H^{\pm}}=170\,{\rm GeV}$, and $\mu_{2}=20\,{\rm GeV}$.
• Figure 5: (a) Ratio of the decay branching ratios of $h_{SM}\to\gamma\gamma$ in the DSDM and the SM; (b) suppression factor of the usual decay modes compared to the SM for $m_{H^{0}}=40,\,50,\,60\,{\rm GeV}$. Here we have chosen $\Delta m_{A^{0}H^{0}}=10\,{\rm GeV}$ and $\mu_{2}=20\,{\rm GeV}$.