Scaling and Goldstone effects in a QCD with two flavours of adjoint quarks

We study QCD with two Dirac fermions in the adjoint representation at finite temperature by Monte Carlo simulations. In such a theory the deconfinement and chiral phase transitions occur at different temperatures. We locate the second-order chiral transition point at βc=5.624(2) and show that the scaling behaviour of the chiral condensate in the vicinity of βc is in full agreement with that of the 3d O(2) universality class, and to a smaller extent comparable to the 3d O(6) class. From the previously determined first-order deconfinement transition point βd=5.236(3) and the two-loop beta function we find the ratio Tc/Td≈7.8(2). In the region between the two phase transitions we explicitly confirm the quark mass dependence of the chiral condensate which is expected due to the existence of Goldstone modes like in 3d O(N) spin models. At the deconfinement transition 〈ψ¯ψ〉 shows a gap, and below βd, it is nearly mass-independent for fixed β.