How well do we need to measure Higgs boson couplings?

TL;DR

The paper asks how precisely Higgs couplings must be measured to reveal new physics beyond the Standard Model. It defines a concrete criterion for the needed precision and applies it to three motivated frameworks—mixed-in singlet mixing, composite (SILH) Higgs scenarios, and MSSM Higgs bosons—to bound maximal deviations consistent with no additional EWSB states observed at the LHC. The analysis finds vector-boson couplings typically require corrections at the 6–8% level (or smaller in some cases), while fermion couplings can range from a few percent to tens of percent, potentially reaching large values in SUSY contexts. Additionally, projected LHC sensitivities at 14 TeV with 3 ab^-1 are on the order of 8–15% for key channels, providing practical guidance for future measurements and collider design.

Abstract

Most of the discussion regarding the Higgs boson couplings to Standard Model vector bosons and fermions is presented with respect to what present and future collider detectors will be able to measure. Here, we ask the more physics-based question of how well do we need to measure the Higgs boson couplings? We first present a reasonable definition of "need" and then investigate the answer in the context of various highly motivated new physics scenarios: supersymmetry, mixed-in hidden sector Higgs bosons, and a composite Higgs boson. We find the largest coupling deviations away from the SM Higgs couplings that are possible if no other state related to EWSB is directly accessible at the LHC. Depending on the physics scenario under consideration, we find targets that range from less than 1% to 10% for vector bosons, and from a few percent to tens of percent for couplings to fermions.

Figures (10)

• Figure 1: We show above the area in the $s_h^2-m_H$ plane allowed by electroweak precision tests at the 90$\%$ CL in the presence of a mixed-in singlet Higgs boson. We also show the detectability curve (solid line) above which the scalar $H$ is detectable with 100 fb$^{-1}$ data at the 14 TeV LHC. The maximum allowed $s_h^2$-value that can both evade detection and be consistent with precision electroweak constraints is thus given by the intersection of the two lines and is $s_h^2=0.12$.
• Figure 2: Deviations of composite Higgs couplings to vector bosons from SM values ($\Delta g_V/g_V^{SM}$) for $c_H=1$. Note that whereas we have given the coupling deviations only to first order in $\xi$ in eq. \ref{['vec']}, in this figure we have used the expression $(1/\sqrt{1+c_H \xi}-1)$ for the coupling deviation, still neglecting terms suppressed by $g/g_\rho$.
• Figure 3: $\Delta g_V/g_V^{SM}$ as a function of $m_A$ with $\Delta_{22}$, the radiative correction to the ${\cal M}^2_{22}$ entry of the Higgs mass matrix, chosen to obtain $m_h=125\, {\rm GeV}$. Other values of $\Delta_{ij}=0$. For the solid line we have taken $\tan \beta =30$ and for the dashed line $\tan \beta =5$.
• Figure 4: We plot $\Delta g_u/g_u^{SM}$ as a function of $m_A$ with $\Delta_{22}$, the radiative correction to the ${\cal M}^2_{22}$ entry of the Higgs mass matrix, chosen to obtain $m_h=125\, {\rm GeV}$. Other values of $\Delta_{ij}=0$. For the solid line we have taken $\tan \beta =30$ and for the dashed line $\tan \beta =5$.
• Figure 5: We plot $\Delta g_d/g_d^{SM}$ as a function of $m_A$ with $\Delta_{22}$, the radiative correction to the ${\cal M}^2_{22}$ entry of the Higgs mass matrix, chosen to obtain $m_h=125\, {\rm GeV}$. Other values of $\Delta_{ij}=0$. For the solid line we have taken $\tan \beta =30$ and for the dashed line $\tan \beta =5$.