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 $\sim 125\mathrm{G}\mathrm{e}\mathrm{V}$ we find that the maximum value of the fourth generation quark mass is $\sim 300\mathrm{G}\mathrm{e}\mathrm{V}$, which is already in conflict with bounds from direct searches.