In this work we explicitly demonstrate the equivalence of covariant (Feynman) perturbation
theory with noncovariant light-front perturbation theory (LEPT) for lowest-order self-energy
corrections in the (1+ 1)-dimensional Yukawa model. We also perform calculations in
oldfashioned perturbation theory in the infinite-momentum frame (OFP T∞) to elucidate the
differences between LFPT and OFP T∞.

We have explicitly demonstrated the equivalence of lowest-order mass corrections in LFPT
with thecovariant results. Further, by comparison with the OFPT calculations, we were able
to elucidate thedifferences between LFPT and OFPT. We have also clarified the role of
operator ordering in the light-front Hamiltonian.