The Higgs Decay Width in Multi-Scalar Doublet Models

TL;DR

This paper investigates a two-Higgs-doublet extension with MFV in which a heavy scalar doublet $S$ at the TeV scale can be effectively invisible at the LHC, yet significantly alters the light Higgs decay width to $b\bar{b}$. By integrating out $S$, it derives an effective operator that shifts ${\rm BR}(h\to b\bar{b})$ and shows that the Higgs branching ratios to $\gamma\gamma$ and $\tau^+\tau^-$ can be either suppressed or enhanced through changes in the total width, with explicit parametrizations illustrating potential factors from modest to enormous. The paper analyzes the production and decay of the heavy scalar $S_R$, finding that $b\bar b\to S_R$ can yield observable rates in some regions, while many regions render $S_R$ effectively undetectable within the first few hundred fb$^{-1}$. Overall, the work highlights that Higgs-property measurements at the LHC provide a powerful indirect probe of hidden TeV-scale new physics, and the conclusions extend to models with more scalar doublets.

Abstract

We show that there are regions of parameter space in multi-scalar doublet models where, in the first few hundred inverse femtobarns of data, the new charged and neutral scalars are not directly observable at the LHC and yet the Higgs decay rate to b bbar is changed significantly from its standard model value. For a light Higgs with a mass less than 140 GeV, this can cause a large change in the number of two photon and tau tau Higgs decay events expected at the LHC compared to the minimal standard model. In the models we consider, the principle of minimal flavor violation is used to suppress flavor changing neutral currents. This paper emphasizes the importance of measuring the properties of the Higgs boson at the LHC; for a range of parameters the model considered has new physics at the TeV scale that is invisible, in the first few hundred inverse femtobarns of integrated luminosity at the LHC, except indirectly through the measurement of Higgs boson properties.

Figures (3)

• Figure 1: The one loop contribution to $b \rightarrow s \, \gamma$ due to the doublet S.
• Figure 2: The production cross section of $b \, \bar{b} \to {S}_R$ for the parameter choices of $\eta_D=10$ and $g_1=0.5$. The production cross section (for the same parameter choices) for $g \, g \to {S}_R$ is approximately $0.2 \, {\rm fb}$ for $M \sim 800 \, {\rm GeV}$ and falls quickly with increasing $M$ and thus is not shown. The curve was generated using CTEQ5 parton distribution functions Lai:1999wy. The $b$ and $t$ masses were evaluated at $\mu= 1 \, {\rm TeV}$ using leading log running. We chose $\Lambda_{QCD} = 0.1\, {\rm GeV}$ and used the initial values ${m}_b = 4.26 \, {\rm GeV}$ determined from converting the result of the $1S$ fit to the b quark mass Bauer:2004ve and the value $m_t = 170 \, {\rm GeV}$ from the PDG PDBook
• Figure 3: Branching fractions for ${S}_R$ decays as a function of the it's mass $M$. The solid black curve denotes the branching ratio for $S_{R} \rightarrow {b \, \bar{b}}$, the gray very-long-dashed curve denotes $S_R\to hh$, the red short-dashed curve is for $S_{R} \rightarrow {t \, \bar{t}}$, the blue medium-dashed curve is for $S_{R} \rightarrow {W^+ W^-}$, and the green long-dashed curve is for ${S}_R\to Z^0 Z^0$. We have not shown the curve for $S_R\to hhh$ in order to avoid too much clutter. These curves were generated with the parameter choices of $\eta_D=10$ and $g_1=0.5$.