TTP02-03 The radiative return at small angles: virtual corrections

Virtual corrections for electron–positron annihilation into one real and one off-shell photon of invariant mass $Q^2$ are evaluated. Special attention is paid to those configurations where the real photon is collinear with the beam direction. This calculation is an important ingredient of a Monte Carlo program, which simulates events with tagged photons from initial-state radiation, including NLO corrections.