Higgs Particles in the Standard Model and Supersymmetric Theories

TL;DR

This thesis provides a comprehensive theoretical assessment of Higgs bosons in the SM and MSSM, focusing on how to reconstruct the Higgs potential through collider observables at the LHC, future $e^+e^-$ linear colliders, and $\gamma\gamma$ colliders. It analyzes production mechanisms, lifetimes, and self-couplings, with detailed treatment of higher-order QCD/electroweak corrections and resonance effects, outlining strategies to measure $M_H$, $\Gamma_{tot}$, and trilinear couplings like $\lambda_{HHH}$ and $\lambda_{Hhh}$. A key finding is that $\gamma\gamma$ collisions offer a powerful complement to the LHC for heavy MSSM Higgs discovery (via $H/A\to b\bar b$) and enable model-independent lifetime measurements through $\gamma\gamma$ fusion, while linear colliders can achieve precision determinations of $\lambda_{HHH}$ (~20% at $\sqrt{s}\approx500$ GeV) and, in the MSSM, access multiple trilinear couplings through continuum and resonant processes. Overall, the work illuminates how joint collider programs could validate the Higgs mechanism, constrain MSSM parameter space, and map the Higgs potential, with practical implications for experimental planning and data interpretation.

Abstract

This thesis presents a theoretical analysis of the properties of the Higgs bosons in the Standard Model (SM) and the minimal supersymmetric extension (MSSM), which can be investigated at the LHC and $e^+e^-$ linear colliders. The final goal is the reconstruction of the Higgs potential and thus the verification of the Higgs mechanism. MSSM Higgs boson production processes at future $γγ$ colliders are calculated in several decay channels. Heavy scalar and pseudoscalar Higgs bosons can be discovered in the $b\bar{b}$ final state in the investigated mass range 200 to 800 GeV for moderate and large values of $\tanβ$. The $τ^+τ^-$ channel provides a heavy Higgs boson discovery potential for large values of $\tanβ$. Several mechanisms that can be exploited at $e^+e^-$ linear colliders for the measurement of the lifetime of a SM Higgs boson in the intermediate mass range are analysed. In the $WW$ mode, the lifetime of Higgs scalars with masses below $\sim 160$ GeV can be determined with an error less than 10%. The reconstruction of the Higgs potential requires the measurement of the Higgs self-couplings. The SM and MSSM trilinear Higgs self-couplings are accessible in double and triple Higgs production. A theoretical analysis is presented in the relevant channels at the LHC and $e^+e^-$ linear colliders. For high luminosities, the SM trilinear Higgs self-coupling can be measured with an accuracy of 20% at a 500 GeV $e^+e^-$ linear collider. The MSSM coupling among three light Higgs bosons has to be extracted from continuum production. The other trilinear Higgs couplings are measurable in a restricted range of the MSSM parameter space. At the LHC, the $Hhh$ coupling can be probed in resonant decays.

Figures (44)

• Figure 1: The Yukawa couplings of the neutral CP-even Higgs bosons to up- and down-type quarks, respectively, in units of the SM couplings as a function of $M_A$ for two values of $\tan\beta =3,50$ and vanishing mixing.
• Figure 2: Higgs production cross sections at the LHC for $\sqrt{s} = 14$ TeV as a function of the Higgs mass. The full QCD corrections have been included apart from the processes $Hb\bar{b}$, $Ht\bar{t}$ where the QCD-corrected results are unknown spirahabil.
• Figure 3: Expected significances in the various SM Higgs search channels at ATLAS as a function of the Higgs mass for an integrated luminosity of 100 fb$^{-1}$atlascms.
• Figure 4: Significances for the SM Higgs boson search as a function of the Higgs mass at CMS for an integrated luminosity of 100 fb$^{-1}$kinnunen.
• Figure 5: The cross sections of the various Higgs production mechanisms at the Tevatron as a function of the Higgs mass tevspir. The plot shows the full QCD corrected results for gluon fusion $gg\to H$, vector boson fusion $qq \to qqVV \to qqH$ and Higgs-strahlung $q\bar{q} \to V^* \to VH$. The QCD corrections to the associated production processes $gg,q\bar{q} \to Ht\bar{t}, Hb\bar{b}$ are unknown and therefore not included.