Baryon and meson screening masses

In a strongly coupled quark-gluon plasma, collective excitations of gluons and quarks should dominate over the excitation of individual quasifree gluon and quark modes. To explore this possibility, we computed screening masses for ground-state light-quark mesons and baryons at leading order in a symmetry-preserving truncation scheme for the Dyson-Schwinger equations using a confining formulation of a contact interaction at nonzero temperature. Meson screening masses are obtained from Bethe-Salpeter equations, and baryon analogues from a novel construction of the Faddeev equation, which employs an improved quark-exchange approximation in the kernel. Our treatment implements a deconfinement transition that is coincident with chiral symmetry restoration in the chiral limit, when both transitions are second order. Despite deconfinement, in all T 0 bound-state channels, strong correlations persist above the critical temperature, T > T-c; and, in the spectrum defined by the associated screening masses, degeneracy between parity-partner correlations is apparent for T greater than or similar to 1.3T(c). Notwithstanding these results, there are reasons (including Golberger-Treiman relations) to suppose that the inertial masses of light-quark bound states, when they may be defined, vanish at the deconfinement temperature, and that this is a signal of bound-state dissolution. Where a sensible comparison is possible, our predictions are consistent with results from contemporary numerical simulations of lattice-regularized QCD.