Discovery potential of radiative neutralino production at the ILC
  We study radiative neutralino production e^+e^- \to \tilde\chi^0_1 \tilde\chi^0_1\gamma at the linear collider with longitudinally polarised beams. We consider the Standard Model background from radiative neutrino production e^+e^- \to \nu \bar\nu \gamma, and the supersymmetric radiative production of sneutrinos e^+e^- \to \tilde\nu \tilde\nu^\ast \gamma, which can be a background for invisible sneutrino decays. We give the complete tree-level formulas for the amplitudes and matrix elements squared. In the Minimal Supersymmetric Standard Model, we study the dependence of the cross sections on the beam polarisations, on the parameters of the neutralino sector, and on the selectron masses. We show that for bino-like neutralinos longitudinal polarised beams enhance the signal and simultaneously reduce the background, such that statistics is significantly enhanced. We point out that there are parameter regions where radiative neutralino production is the only channel to study SUSY particles, since heavier neutralinos, charginos and sleptons are too heavy to be pair-produced in the first stage of the linear collider with \sqrt{s}=500 GeV. 
Herbi K. Dreiner, Olaf Kittel, Ulrich Langenfeld