A General Approach To Photon Radiation Off Fermions

TL;DR

This paper introduces a generalized subtraction formalism for photon radiation off fermions, effectively handling singularities in numerical phase-space integrations for processes with arbitrary masses and helicities.

Contribution

It extends the dipole formalism to include massive and helicity-dependent configurations, improving the accuracy of radiative correction calculations.

Findings

Demonstrates the formalism's application to photon corrections in various particle processes.

Shows the method's efficiency in managing collinear singularities for small fermion masses.

Provides a versatile tool for precise radiative correction computations in particle physics.

Abstract

Soft or collinear photon emission potentially poses numerical problems in the phase-space integration of radiative processes. In this paper, a general subtraction formalism is presented that removes such singularities from the integrand of the numerical integration and adds back the analytically integrated contributions that have been subtracted. The method is a generalization of the dipole formalism of Catani and Seymour, which was formulated for NLO QCD processes with massless unpolarized particles. The presented formalism allows for arbitrary mass and helicity configurations in processes with charged fermions and any other neutral particles. Particular attention is paid to the limit of small fermion masses, in which collinear singularities cause potentially large corrections. The actual application and the efficiency of the formalism are demonstrated by the discussion of photonic corrections to the processes \gamma \gamma --> t \bar t (\gamma), e^- \gamma --> e^- \gamma (\gamma), and \mu^+ \mu^- --> \nu_e \bar\nu_e (\gamma).