Disentangling intertwined embedded states and spin effects in light-front quantization - art. no. 074014

The common belief of equivalence between the manifestly covariant calculati on and the LF (light-front) calculation linked by the LF energy integration of the Feynman amplitude is not always realized. Our example of a light-fr ont calculation with a fermion loop explicitly shows that the persistent en d-point singularity in the nonvalence contribution to the bad component of the current J(-) leads to an infinitely different result from that obtained by the covariant Feynman calculation unless the divergence is properly sub tracted. Ensuring the equivalence to the Feynman amplitude, we have identif ied the divergent term that needs to be removed from J(-). Only after this term is subtracted is the result covariant and then it satisfies current co nservation. The same calculation with the boson loop, however, does not exh ibit such a singular behavior and without any adjustment yields a result id entical to the Feynman amplitude. Numerical estimates of the nonvalence con tributions are presented for the cases of both fermion and boson constituen ts.