ProbingCP-violating Higgs contributions inγγ→ff¯through fermion polarization

We discuss the use of fermion polarization for studying neutral Higgs bosonsat a photon collider. To this aim we construct polarization asymmetries whichcan isolate the contribution of a Higgs boson $\phi$ in $\gamma\gamma\to f \barf$, $f=\tau/t$, from that of the QED continuum. This can help in gettinginformation on the $\gamma\gamma\phi$ coupling in case $\phi$ is a CPeigenstate. We also construct CP-violating asymmetries which can probe CPmixing in case $\phi$ has indeterminate CP. Furthermore, we take the MSSM withCP violation as an example to demonstrate the potential of these asymmetries ina numerical analysis. We find that these asymmetries are sensitive to thepresence of a Higgs boson as well as its CP properties over a wide range ofMSSM parameters. In particular, the method suggested can cover the region wherea light Higgs boson may have been missed by LEP due to CP violation in theHiggs sector, and may be missed as well at the LHC.Comment: 14 pages, 14 figures, typeset in revtex4. Version which has appeared in Physical Review D; typos in two references correcte