Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders

Top quark pair production at photon-photon colliders is studied in a low scale quantum gravity scenario. From the dependence of the cross sections on the spin configuration of the top quark and antiquark, we introduce a new observable, top spin asymmetry. It is shown that there exists a special top spin basis where with the polarized parent electron beams the top spin asymmetry vanishes in the standard model but retains substantial values with the large extra dimension effects. We also present lower bounds of the quantum gravity scale (Formula presented) from total cross sections with various combinations of the laser, electron beam, and top quark pair polarizations. The measurements of the top spin state (Formula presented) with unpolarized initial beams are shown to be most effective, enhancing by about 5% the (Formula presented) bounds with respect to the totally unpolarized case.