Incorporating instantaneous parts in the LFD Yukawa model

We have treated the box diagram as an example to get a better understanding of the influence of the instantaneous parts. The expressions of the kernels are derived using the light-front time-ordered (LFTO) box diagrams corresponding to the covariant box diagram. Knowing the expressions for the kernels we discuss the divergences in these expressions. We will show that the zero modes do not cause any problems neither in the propagating LFTO-diagrams nor in the instantaneous diagrams. The logarithmic ultraviolet divergence, 1/p12, is present in all LFTO-diagrams and cannot be removed by adding propagating and instantaneous diagrams. (author)