Higgs Boson Theory and Phenomenology

TL;DR

This review argues that precision electroweak data favor a weakly-coupled Higgs sector and analyzes both the Standard Model Higgs and the MSSM Higgs sector as realizations of electroweak symmetry breaking. It provides a comprehensive treatment of SM Higgs properties, decay modes, production mechanisms, and collider search strategies, including QCD corrections and the potential for precision measurements at the LHC and future linear colliders. It then examines the MSSM Higgs sector, highlighting radiative corrections, decoupling behavior, CP-violating possibilities, and the resulting phenomenology across representative parameter spaces. The work concludes that current and future colliders have robust discovery potential for at least one Higgs state and that precision Higgs measurements are essential to validate the mechanism of electroweak symmetry breaking and to probe supersymmetric structure.

Abstract

Precision electroweak data presently favors a weakly-coupled Higgs sector as the mechanism responsible for electroweak symmetry breaking. Low-energy supersymmetry provides a natural framework for weakly-coupled elementary scalars. In this review, we summarize the theoretical properties of the Standard Model (SM) Higgs boson and the Higgs sector of the minimal supersymmetric extension of the Standard Model (MSSM). We then survey the phenomenology of the SM and MSSM Higgs bosons at the Tevatron, LHC and a future e+e- linear collider. We focus on the Higgs discovery potential of present and future colliders and stress the importance of precision measurements of Higgs boson properties.

Figures (10)

• Figure 1: (a) The "blueband plot" shows $\Delta \chi^2\equiv \chi^2-\chi^2_{\min}$ as a function of the Standard Model Higgs mass lepewwg. The solid line is a result of a global fit using all data; the band represents the theoretical error due to missing higher order corrections. The rectangular shaded region shows the 95% CL exclusion limit on the Higgs mass from direct searches at LEP LEPHiggs. (b) Probability distribution function for the Higgs boson mass, including all available direct and indirect data erler. The probability is shown for 1 GeV bins. The shaded and unshaded regions each correspond to an integrated probability of 50%
• Figure 2: (a) The upper hambye and the lower quiros Higgs mass bounds as a function of the energy scale $\Lambda$ at which the Standard Model breaks down, assuming $M_t=175$ GeV and $\alpha_s(m_Z)=0.118$, taken from ref. Riesselmann. The shaded areas above reflect the theoretical uncertainties in the calculations of the Higgs mass bounds. (b) Following ref. murayama, a reconsideration of the $\Lambda$vs. Higgs mass plot with a focus on $\Lambda<100$ TeV. Precision electroweak measurements restrict the parameter space to lie below the dashed line, based on a 95% CL fit that allows for nonzero values of $S$ and $T$ and the existence of higher dimensional operators suppressed by $v^2/\Lambda^2$. The unshaded area has less than one part in ten fine-tuning.
• Figure 3: Branching ratios of the dominant decay modes of the Standard Model Higgs boson as a function of Higgs mass for $m_{h_{\rm SM}}\leq 200$ GeV, taken from ref. 9. These results have been obtained with the program HDECAYhdecay, and include QCD corrections beyond the leading order DSZ. The shaded bands represent the variations due to the uncertainties in the input parameters: $\alpha_s(M_Z^2) = 0.120 \pm 0.003$, $\overline{m}_b(M_b) = 4.22 \pm 0.05$ GeV, $\overline{m}_c(M_c) = 1.22 \pm 0.06$ GeV, and $M_t = 174 \pm 5$ GeV.
• Figure 4: (a) Branching ratios of the Standard Model Higgs boson as a function of Higgs mass. Two-boson [fermion-antifermion] final states are exhibited by solid [dashed] lines. As compared with fig. \ref{['fg:1']}, a larger range of Higgs masses and branching ratios are shown. (b) The total width of the Standard Model Higgs boson is shown as a function of its mass. For comparison, we exhibit the widths of the two CP-even scalars, $h$ and $H$ of the MSSM for two different choices of MSSM parameters ($\tan\beta=3$ and 30 in the maximal mixing scenario; the onset of the $H\to hh$ and $H\to t\bar{t}$ thresholds in the $\tan\beta=3$ curve are clearly evident). The central values of $\alpha_s$, $\overline{m}_b(M_b)$ and $\overline{m}_c(M_c)$ quoted in the caption of fig. \ref{['fg:1']} are employed in both (a) and (b).
• Figure 5: Higgs production cross-sections (in units of pb) at the Tevatron [$\sqrt{s}=2$ TeV], for the various production mechanisms as a function of the Higgs mass, taken primarily from refs. 9 and private. The full NLO QCD-corrected results are employed for the gluon fusion $gg \to h_{\rm SM}$, vector boson fusion $qq\to V^*V^*qq \to h_{\rm SM} qq$ (here, $qq$ refers to both $ud$ and $q\bar{q}$ scattering), Higgs-strahlung processes $q\bar{q} \to V^* \to Vh_{\rm SM}$ (where $V=W^\pm$, $Z$), $b\bar{b}\to h_{\rm SM}$ (taken from ref. DSSW), and $gg,q\bar{q} \to h_{\rm SM} t\bar{t}$. Tree-level cross-sections are exhibited for $gg,q\bar{q} \to h_{\rm SM} b\bar{b}$. In the latter case, the cross-section has been computed with a running $b$-quark mass, $\alpha_s$ and the parton distribution functions all evaluated at the corresponding Higgs mass.