Goldstone theorem and diquark confinement beyond rainbow-ladder approximation

The quark Dyson-Schwinger equation and meson Bethe-Salpeter equation are studied in a truncation scheme that extends the rainbow-ladder approximation such that, in the chiral limit, the isovector, pseudoscalar meson remains massless. Repulsive contributions, which appear at higher order in the Bethe-Salpeter kernel, eliminate the bound state pole in the quark-quark (diquark) channel that is present in rainbow-ladder approximation. The net effect of higher order terms on the meson bound state masses is small.