  We use lattice simulations to compute the baryon spectrum of SU(4) lattice
gauge theory coupled to dynamical fermions in the fundamental and two-index
antisymmetric (sextet) representations simultaneously. This model is closely
related to a composite Higgs model in which the chimera baryon made up of
fermions from both representations plays the role of a composite top-quark
partner. The dependence of the baryon masses on each underlying fermion mass is
found to be generally consistent with a quark-model description and large-Nc
scaling. We combine our numerical results with experimental bounds on the scale
of the new strong sector to derive a lower bound on the mass of the top
partner.
