Supersymmetric Large Extra Dimensions Are Small and/or Numerous

TL;DR

This work shows that incorporating supersymmetry into large extra-dimension scenarios predicts a very light graviphoton, the spin-1 partner of the graviton, whose mass and couplings are tightly constrained by the underlying higher-dimensional SUSY. The authors derive leading dimension-4 and dimension-5 couplings, explore microscopic origins on branes and in the bulk, and compute production and scattering cross sections, highlighting that dimension-4 couplings can dominate at low energies. Supernova bounds severely constrain the gravity scale $M_s$ and the number of extra dimensions $n$, often requiring $n \ge 4$ (or loop-suppressed couplings) to keep TeV-scale gravity viable. The paper also provides a framework for distinguishing graviphoton exchange from graviton effects in collider processes, though practical identification is hindered by model dependence and potential contaminations from heavier string states.

Abstract

Recently, a scenario has been proposed in which the gravitational scale could be as low as the TeV scale, and extra dimensions could be large and detectable at the electroweak scale. Although supersymmetry is not a requirement of this scenario, it is nevertheless true that its best-motivated realizations arise in supersymmetric theories (like M theory). We argue here that supersymmetry can have robust, and in some instances fatal, implications for the expected experimental signature for TeV-scale gravity. The signature of the supersymmetric version of the scenario differs most dramatically from what has been considered in the literature because mass splittings within the gravity supermultiplet in these models are extremely small, implying in particular the existence of a very light spin-one superpartner for the graviton. We compute the implications of this graviphoton, and show that it can acquire dimension-four couplings to ordinary matter which can strongly conflict with supernova bounds.

Figures (7)

• Figure 1: The Feynman graphs contributing to photon-graviphoton production. The graviphoton-fermion interaction here is a sum of the dimension-four helicity-preserving interaction of Eq. (\ref{['dimfour']}) and the dimension-five helicity-flipping interaction of Eq. (\ref{['dimfive']}).
• Figure 2: The differential cross section for $e^+e^-\to\gamma + GP$, against photon energy, due to the dimension-four couplings of Eq. (\ref{['dimfour']}). The plot assumes an initial electron energy $E_e = 100$ GeV, a minimum photon transverse energy $\omega_{ T} \ge 10$ GeV, and $M_s = 1000$ GeV. The solid line uses $n=6$, the long-dashed line $n=4$ and the short-dashed line $n=2$.
• Figure 3: The differential cross section for $e^+e^-\to\gamma + GP$, against photon scattering angle in the CM frame, arising due to the dimension-four couplings of Eq. (\ref{['dimfour']}). The plot assumes an initial electron energy $E_e = 100$ GeV, a minimum photon transverse energy $\omega_{ T} \ge 10$ GeV, and $M_s = 1000$ GeV. The solid line uses $n=6$, the long-dashed line $n=4$ and the short-dashed line $n=2$.
• Figure 4: The differential cross section for $e^+e^-\to\gamma + GP$, against photon energy, due to the dimension-five couplings of Eq. (\ref{['dimfive']}). The plot assumes an initial electron energy $E_e = 100$ GeV, a minimum photon transverse energy $\omega_{ T} \ge 10$ GeV, and $M_s = 1000$ GeV. The solid line uses $n=6$, the long-dashed line $n=4$ and the short-dashed line $n=2$.
• Figure 5: The differential cross section for $e^+e^-\to\gamma + GP$, against photon scattering angle in the CM frame, arising due to the dimension-five couplings of Eq. (\ref{['dimfive']}). The plot assumes an initial electron energy $E_e = 100$ GeV, a minimum photon transverse energy $\omega_{ T} \ge 10$ GeV, and $M_s = 1000$ GeV. The solid line uses $n=6$, the long-dashed line $n=4$ and the short-dashed line $n=2$.