Probing CP Violation in $\gamma\gamma\to W^+W^-$ with Polarized Photon   Beams
  We demonstrate in a general framework that polarized photons by backscattered laser beams of adjustable frequencies at a TeV linear $e^+e^-$ collider provide us with a very efficient mechanism to probe CP violation in two-photon collisions. CP violation in the process $\gamma\gamma\rightarrow W^+W^-$ is investigated in detail with linearly polarized photon beams. There are two useful CP-odd asymmetries that do not require detailed information on $W$ decay products. The sensitivity to the CP-odd form factors are studied quantitatively by assuming a perfect $e$-$\gamma$ conversion and the 20 fb$^{-1}$ $e^+e^-$ integrated luminosity at the $e^+e^-$ c.m. energies $\sqrt{s}=0.5$ and $1.0$ TeV. The sensitivity is so high that such experiments will allow us to probe new CP violation effects beyond the limits from some specific models with reasonable physics assumptions. We find that a counting experiment of $W^+W^-$ events in the two-photon mode with adjustable laser frequencies can have much stronger sensitivity to the CP-odd $\gamma(\gamma) WW$ form factors than can a $W^+W^-$ decay-correlation experiment with a perfect detector achieve in the $e^+e^-$ mode.   PACS number(s): 14.70.Bh, 14.70.Hp, 13.88.+e 
S.Y. Choi and K. Hagiwara (KEK) and M.S. Baek (Seoul National   University, CTP)