Indirect collider tests for large extra dimensions

Abstract

New physics signatures arising from different sources may be confused when first observed at future colliders. Thus it is important to examine how various scenarios may be differentiated given the availability of only limited information. Arkani-Hamed, Dimopoulous, and Dvali have proposed a model (ADD) of low-scale quantum gravity featuring large extra dimensions. In this model, the exchange of Kaluza-Klein towers of gravitons can manifest themselves through deviations of the observables from the Standard Model predictions. Here, we assess the expected “identification reach” on the ADD model of gravity in large compactified extra dimensions, against the compositeness-inspired four-fermion contact interaction. As basic observables we take the differential cross sections for fermion-pair production at a 0.5–1 TeV electron-positron linear collider with both beams longitudinally polarized. For the four-fermion contact interaction we assume a general linear combination of the individual models with definite chiralities, with arbitrary coupling constants. In this sense, the estimated identification reach on the ADD model can be considered as “model-independent”. In the analysis, we give estimates also for the expected “discovery reaches” on the various scenarios. We emphasize the substantial rˆole of beams polarization in enhancing the sensitivity to the contactlike interactions under consideration.