Higgs Boson Bounds in Three and Four Generation Scenarios

TL;DR

This paper updates bounds on the lightest Higgs boson mass within the Standard Model and MSSM, exploring implications of potential fourth-generation fermions and their impact on theoretical consistency and experimental bounds.

Contribution

It provides new constraints on Higgs mass bounds considering third and fourth generation scenarios, highlighting conditions for MSSM viability and potential signals of new fermions.

Findings

SM vacuum stability bound exceeds MSSM Higgs upper bound in large parameter space.

Detection of Higgs below 134-150 GeV suggests possible fourth-generation fermions.

Fourth-generation fermions can reconcile MSSM with experimental Higgs mass bounds.

Abstract

In light of recent experimental results, we present updated bounds on the lightest Higgs boson mass in the Standard Model (SM) and in the Minimal Supersymmetric extension of the Standard Model (MSSM). The vacuum stability lower bound on the pure SM Higgs boson mass when the SM is taken to be valid up to the Planck scale lies above the MSSM lightest Higgs boson mass upper bound for a large amount of SUSY parameter space. If the lightest Higgs boson is detected with a mass M_{H} < 134 GeV (150 GeV) for a top quark mass M_{top} = 172 GeV (179 GeV), it may indicate the existence of a fourth generation of fermions. The region of inconsistency is removed and the MSSM is salvagable for such values of M_{H} if one postulates the existence of a fourth generation of leptons and quarks with isodoublet degenerate masses M_{L} and M_{Q} such that 60 GeV < M_{L} < 110 GeV and M_{Q} > 170 GeV.