Asymptotic safety And high-energy scattering at the Large Hadron Collider

The fascinating idea that in higher-dimensional models the fundamental scale of gravity, the Planck scale, could be as low as the electroweak scale has stimulated a substantial body of work in the past decade. In addition to solving the hierarchy problem, a low quantum gravity scale also o?ers the exciting prospect that collider experiments become sensitive to the quantum nature of gravity. Quantum gravity signatures include missing energy due to graviton emission, enhancement of standard model reference processes via virtual graviton exchange, or the production and decay of mini black holes. Dedicated searches for all of these are presently under way at the Large Hadron Collider. Previous predictions for colliders have been encumbered by the absence of a complete theory of quantum gravity. However, the recent years have also seen important progress in the understanding of gravity as an asymptotically safe quantum field theory, in which the high-energy behaviour is controlled by an interacting fixed point. The notorious divergences of perturbation theory are thus avoided, and the theory remains predictive at arbitrarily high energies. In this thesis, we investigate the effects of asymptotic safety upon predictions for graviton-mediated processes in higher-dimensions at colliders. We consider single-graviton mediated effects in the Born approximation as well as the multi-graviton exchanges which dominate the forward scattering region at transplanckian energies, as described by the eikonal approximation. Cross sections are derived and a detailed comparison with findings from effective theory is made. Using the PYTHIA event generator we find that for some regions in parameter space quantum gravity effects are enhanced over the semiclassical predictions, as well as over standard model backgrounds. The use of our results to constrain our theory parameters is discussed.