The effects of large extra dimensions on associated tt̄h 0 production at linear colliders ∗

In the framework of the large extra dimensions (LED) model, the effects of LED on the processes γγ → tt̄h0 and e+e− → tt̄h0 at future linear colliders are investigated in both polarized and unpolarized collision modes. The results show that the virtual Kaluza-Klein (KK) graviton exchange can significantly modify the standard model expectations for these processes with certain polarizations of initial states. The process γγ → tt̄h0 with √s = 3.5 TeV allows the effective scale ΛT to be probed up to 7.8 and 8.6 TeV in the unpolarized and Pγ = 0.9, J=2 polarized γγ collision modes, respectively. For the e+e− → tt̄h0 process with √s = 3.5 TeV , the upper limits of ΛT to be observed can be 6.7 and 7.0 TeV in the unpolarized and Pe+ = 0.6, Pe− = 0.8, −+ polarized e+e− collision modes, respectively. We find the γγ → tt̄h0 channel in J = 2 polarized photon collision mode provides a possibility to improve the sensitivity to the graviton tower exchange. PACS: 14.80.-j, 14.80.Cp, 04.50.+h ∗Supported by National Natural Science Foundation of China. 1