  In our previous work [J. Math. Phys. 49, 033513 (2008)] two problems remain
to be resolved. One is that we lack a minimal group to replace GL(4,C), the
other is that the Equation of Motion (EoM) for fermion has no mass term. After
careful investigation we find these two problems are linked by conformal group,
a subgroup of GL(4,C) group. The Weyl group, a subgroup of conformal group, can
bring about the running of mass, charge etc. while making it responsible for
the transformation of interaction vertex. However, once concerning the
generation of the mass term in EoM, we have to resort to the whole conformal
group, in which the generators $K_\mu $ play a crucial role in making vacuum
vary from space-like (or light-cone-like)to time-like. Physically the starting
points are our previous conclusion, $\vec E^2-\vec B^2\neq 0$ for massive
bosons, and the two-photon process yielding $e^+ e^-$ pair. Finally we get to
the conclusion that the mass term of strong interaction is linearly relevant to
(chromo-)magnetic flux as well as angular momentum.
