Chiral limit of a fermion-scalar (1/2) + system in covariant gauges

The homogeneous Bethe-Salpeter equation (BSE) of a (1/2)+ bound system, that has both fermionic and bosonic degrees of freedom, that we call a mock nucleon, is studied in Minkowski space, in order to analyze the chiral limit in covariant gauges. After adopting an interaction kernel built with a one-particle exchange, the chi-BSE is numerically solved by means of the Nakanishi integral representation and light -front projection. Noteworthy, the chiral limit induces a scale invariance of the model and consequently generates a wealth of striking features: (i) it reduces the number of nontrivial Nakanishi weight functions to only one; (ii) the form of the surviving weight function has a factorized dependence on the two relevant variables, compact and noncompact; and (iii) the coupling constant becomes an explicit function of the real exponent governing the power-law falloff of the nontrivial Nakanishi weight function. The thorough investigation at large transverse momentum of light-front Bethe-Salpeter amplitudes, obtained with massive constituents, provides a confirmation of the expected universal power-law falloff, with exponents predicted by our nonperturbative framework. Finally, one can shed light on the exponents that govern the approach to the upper extremum of the longitudinal-momentum fraction distribution function of the mock nucleon, when the coupling constant varies.