Polarized QED splittings of massive fermions and dipole subtraction for non-collinear-safe observables

Understand

Building on earlier work, the dipole subtraction formalism for photonic corrections is extended to various photon--fermion splittings where the resulting collinear singularities lead to corrections that are enhanced by logarithms of small fermion masses.

• The difference to the earlier treatment of photon radiation is that now no cancellation of final-state singularities is assumed, i.e.
• we allow for non-collinear-safe final-state radiation.
• Moreover, we consider collinear fermion production from incoming photons, forward-scattering of incoming fermions, and collinearly produced fermion-antifermion pairs.