Constraining a fourth generation of quarks: non-perturbative Higgs boson mass bounds

TL;DR

This study non-perturbatively determines Higgs boson mass bounds with a heavy fourth quark generation, finding that the upper bound rises modestly while the lower bound increases significantly, constraining the viability of such a generation.

Contribution

It provides the first non-perturbative lattice computation of Higgs mass bounds in the presence of a heavy fourth quark generation, including effects of higher-dimensional operators.

Findings

Upper Higgs mass bound rises modestly with quark mass

Lower Higgs mass bound increases significantly with quark mass

Maximum quark mass compatible with a 125 GeV Higgs is around 300 GeV

Abstract

We present a non-perturbative determination of the upper and lower Higgs boson mass bounds with a heavy fourth generation of quarks from numerical lattice computations in a chirally symmetric Higgs-Yukawa model. We find that the upper bound only moderately rises with the quark mass while the lower bound increases significantly, providing additional constraints on the existence of a straight-forward fourth quark generation. We examine the stability of the lower bound under the addition of a higher dimensional operator to the scalar field potential using perturbation theory, demonstrating that it is not significantly altered for small values of the coupling of this operator. For a Higgs boson mass of $\sim125\mathrm{GeV}$ we find that the maximum value of the fourth generation quark mass is $\sim300\mathrm{GeV}$, which is already in conflict with bounds from direct searches.