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

Old, Rob (2015) Asymptotic safety And high-energy scattering at the Large Hadron Collider. Doctoral thesis (PhD), University of Sussex.

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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.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0770 Nuclear and particle physics. Atomic energy. Radioactivity > QC0793 Elementary particle physics
Depositing User: Library Cataloguing
Date Deposited: 14 Jun 2016 10:17
Last Modified: 14 Jun 2016 10:17

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