Probing the CP nature of the Higgs bosons by top-pair production at photon linear colliders

Abstract

We study effects of heavy Higgs bosons on the top-pair production process at photon linear colliders. The interference patterns between the resonant Higgs-production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the $\gamma\gamma$--Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing top decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process $\gamma\gamma \to t \bar{t} \to (bW^+) (\bar{b}W^-) \to (b f_1 \bar{f}_2) (\bar{b} f_3 \bar{f}_4)$ are presented in terms of the generic $\gamma\gamma \to t \bar{t}$ production amplitudes.