Effects of large extra dimensions on associatedtt¯h0production at linear colliders

Abstract

In the framework of the large extra-dimensions (LED) model, the effects of LED on the processes $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ at future linear colliders are investigated in both polarized and unpolarized collision modes. The results show that the virtual Kaluza-Klein graviton exchange can significantly modify the standard model expectations for these processes with certain polarizations of initial states. The process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ with $\sqrt{s}=3.5\text{ }\mathrm{TeV}$ allows the effective scale ${\ensuremath{\Lambda}}_{T}$ to be probed up to 7.8 and 8.6 TeV in the unpolarized and ${P}_{\ensuremath{\gamma}}=0.9$, $J=2$ polarized $\ensuremath{\gamma}\ensuremath{\gamma}$ collision modes, respectively. For the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ process with $\sqrt{s}=3.5\text{ }\mathrm{TeV}$, the upper limits of ${\ensuremath{\Lambda}}_{T}$ to be observed can be 6.7 and 7.0 TeV in the unpolarized and ${P}_{{e}^{+}}=0.6$, ${P}_{{e}^{\ensuremath{-}}}=0.8$, $\ensuremath{-}+$ polarized ${e}^{+}{e}^{\ensuremath{-}}$ collision modes, respectively. We find the $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}t\overline{t}{h}^{0}$ channel in $J=2$ polarized photon collision mode provides a possibility to improve the sensitivity to the graviton tower exchange.