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

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 similar to 125 GeV we find that the maximum value of the fourth generation quark mass is similar to 300 GeV, which is already in conflict with bounds from direct searches. (c) 2013 Elsevier B.V. All rights reserved.