Graviton production by two photon and electron-photon processes in Kaluza-Klein theories with large extra dimensions

Abstract

We consider the production of gravitons via two photon and electron-photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We show that at electron-positron colliders, the processes ${l}^{+}{l}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}+\mathrm{graviton},$ with $l=e,$ $\ensuremath{\mu},$ can lead to a new signal of low energy gravity of the form ${l}^{+}{l}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}+\mathrm{missing}$ energy which is well above the standard model background. For example, with two extra dimensions, at the Next Linear Collider with a center of mass energy of 500 or 1000 GeV, hundreds to thousands such ${l}^{+}{l}^{\ensuremath{-}}+\mathrm{graviton}$ events may be produced if the scale of the gravitational interactions, ${M}_{D},$ is around a few TeV. At a gamma-electron collider, more stringent bounds may be placed on ${M}_{D}$ via the related reaction ${e}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}{e}^{\ensuremath{-}}G.$ For instance, if a 1 TeV ${e}^{+}{e}^{\ensuremath{-}}$ collider is converted to an electron-photon collider, a bound of $\ensuremath{\sim}10(14) \mathrm{TeV}$ may be placed on the scale ${M}_{D}$ if the number of extra dimensions $\ensuremath{\delta}=2,$ while a bound of $\ensuremath{\sim}4(5) \mathrm{TeV}$ may be placed if $\ensuremath{\delta}=4,$ with unpolarized (right polarized) electron beams.