  The propagation of a high energy quark disturbs the confining QCD vacuum
inducing the currents in Dirac sea. Since quarks possess electric charge, these
induced vacuum quark currents act as a source of soft photon radiation. This
can lead to the enhancement of the soft photon production above the
expectations based on the charged hadron yields and the Low theorem. We
illustrate the phenomenon by using the exactly soluble 1+1 dimensional massless
Abelian gauge model that shares with QCD all of the ingredients involved in
this mechanism: confinement, chiral symmetry breaking, axial anomaly, and the
periodic $\theta$-vacuum. We show that the propagating quark throughout the
process of hadronization induces in the vacuum charged transition currents that
lead to a strong resonant enhancement of the soft photon yield; the Low theorem
however remains accurate in the limit of very soft momenta. We then construct
on the basis of our result a simple phenomenological model and apply it to the
soft photon production in the fragmentation of jets produced in $Z^0$ decays.
We find a qualitative agreement with the recent result from the DELPHI
Collaboration.
