Aspects of quantum gravity and matter

Schröder, Jan (2015) Aspects of quantum gravity and matter. Doctoral thesis (PhD), University of Sussex.

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A quantum theory of gravity remains one of the greatest challenges of contemporary
physics. It is well established that a perturbative treatment of gravity as a quantum field
theory leads to a non-renormalisable setup. However gravity could still exist as a consistent
and predictive quantum field theory on a non-perturbative level. This is explored in
the asymptotic safety scenario which was initially proposed by S. Weinberg.
In this thesis we investigate the ultraviolet behaviour of gravity within the asymptotic
safety conjecture and discuss phenomenological implications. We start out by introducing
the concept of the functional renormalisation group and its application to gravity. This
non-perturbative tool is the technical basis for our investigation of a template quantum
gravity action, namely a function f(R) in the Ricci scalar in four dimensions. We compute
exact fixed point solutions to very high polynomial orders via the development of
a dedicated high performance code. The picture of an interacting UV fixed point that
receives only small quantitative corrections from higher derivative operators is confirmed
and extended.
The results are then expanded to include minimally coupled matter fields and we investigate
the matter effects on the gravitational fixed point. We determine regimes of
compatibility in the vicinity of the purely gravitational setup but also find constraints on
the number of matter fields.
Finally we look at the phenomenological implications of a running Newton's coupling, one
of the key features of the asymptotic safety setup, to graviton-mediated eikonal scattering
amplitudes. In this kinematic regime we investigate the possibility of a TeV-sized fundamental
Planck mass via the introduction of compact extra dimensions. We identify the
fingerprints of asymptotic safety in the t-channel scattering amplitude and find crucial
differences compared to semi-classical computations.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0170 Atomic physics. Constitution and properties of matter Including molecular physics, relativity, quantum theory, and solid state physics
Depositing User: Library Cataloguing
Date Deposited: 09 Jun 2015 10:07
Last Modified: 28 Sep 2015 14:42

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