Second order perturbations of a Schwarzschild black hole: inclusion of   odd parity perturbations
  We consider perturbations of a Schwarzschild black hole that can be of both even and odd parity, keeping terms up to second order in perturbation theory, for the $\ell=2$ axisymmetric case. We develop explicit formulae for the evolution equations and radiated energies and waveforms using the Regge-Wheeler-Zerilli approach. This formulation is useful, for instance, for the treatment in the ``close limit approximation'' of the collision of counterrotating black holes. 
Carlos O. Nicasio, Reinaldo Gleiser, Jorge Pullin