
We present a detailed, allorder study of gluon mass generation within the massless boundstate formalism, which constitutes the general framework for the systematic implementation of the Schwinger mechanism in nonAbelian gauge theories. The main ingredient of this formalism is the dynamical formation of bound states with vanishing mass, which give rise to effective vertices containing massless poles; these latter vertices, in turn, trigger the Schwinger mechanism, and allow for the gaugeinvariant generation of an effective gluon mass. This particular approach has the conceptual advantage of relating the gluon mass directly to quantities that are intrinsic to the boundstate formation itself, such as the 'transition amplitude'' and the corresponding 'boundstate wave function.'' As a result, the dynamical evolution of the gluon mass is largely determined by a BetheSalpeter equation that controls the dynamics of the relevant wave function, rather than the SchwingerDyson equation of the gluon propagator, as happens in the standard treatment. The precise structure and fieldtheoretic properties of the transition amplitude are scrutinized in a variety of independent ways. In particular, a parallel study within the linearcovariant (Landau) gauge and the backgroundfield method reveals that a powerful identity, known to be valid at the level of conventional Green's functions, also relates the background and quantum transition amplitudes. Despite the differences in the ingredients and terminology employed, the massless boundstate formalism is absolutely equivalent to the standard approach based on SchwingerDyson equations. In fact, a set of powerful relations allows one to demonstrate the exact coincidence of the integral equations governing the momentum evolution of the gluon mass in both frameworks.
