Janus-Facedness of the Pion: Analytic Instantaneous Bethe-Salpeter Models

Instantaneous Bethe-Salpeter Approach to Pseudoscalar Mesons

Light pseudoscalar mesons are Janus-type particles: Within quantum chromodynamics, they must be described as bound states of its fundamental degrees of freedom and as the (pseudo-) Goldstone bosons of its spontaneously broken chiral symmetry. This janiform nature of pions and kaons may be easily accommodated by the Bethe-Salpeter formalism in its instantaneous limit: Starting from the general behaviour of the Bethe-Salpeter solutions for light pseudoscalar mesons at large Euclidean momenta, we provide the exact relationship between the solutions of our bound-state equation and the underlying i…