Asymptotic Safety in Particle Physics and Quantum Gravity
Manuel Reichert, University of Southern Denmark, Odense
Abstract:
Physicists want to describe nature on all length scales, from the size of the observable universe down to elementary particles. In quantum field theories, an essential tool to connect the physics of different length scales is the Renormalisation Group. It allows identifying the relevant degrees of freedom at each length scale. We use this tool to zoom into smaller and smaller length scales of quantum field theories. If we demand that our theory is valid on all length scales, it must become scale invariant at small length scales. Such scenarios are described by fixed points of the Renormalisation Group flow. Well-known examples are asymptotically free theories, such as quantum chromodynamics, where the theory becomes non-interacting at small length scales. A natural generalisation of asymptotic freedom is asymptotic safety, where the theory is scale-invariant, but interacting at small length scales. Some quantum field theories with this property were recently discovered and there are even indications that this concept might lead to a consistent theory of quantum gravity. The Standard Model of Particle Physics is neither asymptotically free nor safe. Instead, some couplings diverge at small length scales, signalling the breaks down of the theory. We will ask the question, which new physics beyond the Standard Model is needed to make it an asymptotically safe theory and how does quantum gravity help here.
