Higgs boson production and decay: Effects from light third generation and vectorlike matter

Abstract

We study the implications of light third generation sparticles on the production cross section and decay widths of a light $CP$-even Higgs boson. For simplicity, we consider scenarios in which only one of the sfermions from the third generation is light. For each case, we attempt to explain the apparently large enhancement in the Higgs production and decay in the diphoton channel with small deviations in the $ZZ$ channel. In the minimal supersymmetric standard model (MSSM) framework we find that only a light stau can explain these observations while keeping the lightest $CP$-even Higgs boson mass in the interval $123\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}127\text{ }\text{ }\mathrm{GeV}$. For the light stop scenario, the observations related to the diphoton and $ZZ$ channel can be accommodated but, in order to satisfy the Higgs mass bound, one needs to go beyond the MSSM. In particular, we invoke vectorlike particles with masses around a TeV. These new particles preserve gauge coupling unification and provide additional contributions to the Higgs mass. With these new contributions a 126 GeV Higgs mass is easily achieved. We also find that with only a light sbottom quark, the above mentioned excess is hard to accommodate.