Searching for string resonances in e^+e^- and \gamma \gamma collisions

TL;DR

This paper explores how low-scale superstring theories could produce detectable Regge excitations at future electron-positron and gamma-gamma colliders, providing model-independent signatures and specific angular distribution predictions.

Contribution

It analyzes Regge excitations in string theory at colliders, identifying universal properties and distinctive angular distributions for detection.

Findings

Gamma gamma to e+ e- proceeds via spin-2 Regge state.

String scale up to 4 TeV detectable at 11σ with 5 TeV collider.

Predicted 1/3 ratio of spin-2 to spin-1 contributions in e+e- annihilation.

Abstract

If the fundamental mass scale of superstring theory is as low as few TeVs, the massive modes of vibrating strings, Regge excitations, will be copiously produced at the Large Hadron Collider (LHC). We discuss the complementary signals of low mass superstrings at the proposed electron-positron facility (CLIC), in e^+e^- and \gamma \gamma collisions. We examine all relevant four-particle amplitudes evaluated at the center of mass energies near the mass of lightest Regge excitations and extract the corresponding pole terms. The Regge poles of all four-point amplitudes, in particular the spin content of the resonances, are completely model independent, universal properties of the entire landscape of string compactifications. We show that \gamma \gamma \to e^+ e^- scattering proceeds only through a spin-2 Regge state. We estimate that for this particular channel, string scales as high as 4 TeV can be discovered at the 11\sigma level with the first fb^{-1} of data collected at a center-of-mass energy \approx 5 TeV. We also show that for e^+e^- annihilation into fermion-antifermion pairs, string theory predicts the precise value, equal 1/3, of the relative weight of spin 2 and spin 1 contributions. This yields a dimuon angular distribution with a pronounced forward-backward asymmetry, which will help distinguishing between low mass strings and other beyond the standard model scenarios.