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Gluon mass through massless bound-state excitations

Recent large-volume lattice simulations have established that, in the Landau gauge, the gluon propagator is infrared-finite. The most natural way to explain this observed finiteness is the generation of a nonperturbative, momentum-dependent gluon mass. Such a mass may be generated gauge-invariantly by employing the Schwinger mechanism, whose main assumption is the dynamical formation of massless bound-state excitations. In this work we demonstrate that this key assumption is indeed realized by the QCD dynamics. Specifically, the Bethe-Salpeter equation describing the aforementioned massless excitations is derived and solved under certain approximations, and non-trivial solutions are obtained.