Diphoton signals for Low Scale Gravity in Extra Dimensions

TL;DR

This paper investigates diphoton production as a probe of low-scale gravity in ADD-like extra-dimensional models, where gravity propagates in the bulk and becomes strong at the TeV scale. It shows that photon-photon scattering and diphoton production receive tree-level contributions from Kaluza-Klein gravitons, in contrast to the Standard Model where such processes are loop-suppressed, and derives cross sections and angular distributions that scale with the cutoff $M_S$ and the number of extra dimensions $n$. By comparing with existing data from LEP and the Tevatron and projecting Run II and future $e^+e^-$ colliders, the authors set lower limits on $M_S$ (e.g., $M_S \gtrsim 1.0$–$1.4$ TeV depending on $n$) and estimate substantial sensitivity gains for photon-photon colliders, which can probe higher $M_S$ due to the tree-level gravity contributions. The work highlights diphoton channels as a powerful and distinctive testbed for TeV-scale gravity and extra dimensions, with gamma-gamma colliders offering the best potential reach among the studied facilities.

Abstract

Gravity can become strong at the TeV scale in the theory of extra dimensions. An effective Lagrangian can be used to describe the gravitational interactions below a cut-off scale. In this work, we study the diphoton production in $γγ$, $p\bar p$, and $e^+ e^-$ collisions in the model of low scale gravity. Since in the standard model photon-photon scattering only occurs via box diagrams, the cross section is highly suppressed. Thus, photon-photon scattering opens an interesting opportunity for studying the new gravity interaction, which allows tree-level photon couplings. In addition, we also examine the diphoton production at hadronic and $e^+ e^-$ colliders. We derive the limits on the cut-off scale from the available diphoton data and also estimate the sensitivity reach in Run II at the Tevaton and at the future linear $e^+ e^-$ colliders.

Figures (5)

• Figure 1: (a) The total cross sections and (b) the differential distribution $d\sigma/ d |\cos\theta_\gamma|$ for $\gamma\gamma \to \gamma\gamma$ for the low scale gravity model and for the SM. A cut of $|\cos \theta_\gamma| < \cos 30^\circ$ is imposed.
• Figure 2: The sensitivity reach on $M_S$ versus $\sqrt{s_{\gamma\gamma}}$ using the process $\gamma\gamma \to \gamma\gamma$, by requiring the signal to be 5% or 10% of the SM prediction. A cut of $|\cos \theta_\gamma| < \cos 30^\circ$ is imposed.
• Figure 3: The differential distribution $d\sigma/dM_{\gamma\gamma}$ versus $M_{\gamma\gamma}$ for diphoton production at the 2 TeV Tevatron for the SM and for the low scale gravity with $M_S=1.5,\;2$ TeV and $n=2,4$. Cuts of $|\eta_\gamma|<1$ and $p_{T\gamma}>20$ GeV are imposed.
• Figure 4: (a) The total cross section versus $\sqrt{s}$ and (b) the differential distribution $d\sigma/ d |\cos\theta |$ for $e^+ e^- \to \gamma\gamma$ for the SM and for the SM plus the new gravity interactions with $n=2,4,6$ and $M_S$ as shown. The $|\cos\theta|<0.95$ is imposed.
• Figure 5: The sensitivity reach on $M_S$ versus $\sqrt{s}$ using the process $e^+ e^- \to \gamma\gamma$, by requiring a 5% or 10% change from the SM prediction. A cut $|\cos\theta|<0.95$ is imposed.