Tau polarization as CP diagnostic for a light Higgs boson at a photon collider

Unfortunately, we have discovered a bug in the computer program which invalidates the numerical results of our paper. While our formulae and the dependencies explained in the paper are correct, the numerical values of the asymmetries presented in the paper go down by more than two orders of magnitude. The plots and the conclusions of the paper as they stand are hence invalid and will have to be changed. We withdraw this paper till we finish this reformulation.