Spectrum of orientifold QCD in the strong coupling and hopping expansion approximation

We use the strong coupling and hopping parameter expansions to calculate the pion and rho meson masses for lattice Yang–Mills gauge theories with fermions in irreducible two-index representations, namely the adjoint, symmetric and antisymmetric. The results are found to be consistent with orientifold planar equivalence, and leading order 1/Nc$1/N_c$ corrections are calculated in the lattice phase. An estimate of the critical bare mass, for which the pion is massless, is obtained as a function of the bare coupling. A comparison to data from the two-flavour SU(2)$\mathit{SU}(2)$ theory with adjoint fermions gives evidence for a bulk phase transition at βc∼2${\beta }_c\sim 2$, separating a pure lattice phase from a phase smoothly connected to the continuum.