Jahn, Peter Thomas (2019)
The Topological Susceptibility of QCD at High Temperatures.
Technische Universität Darmstadt
doi: 10.25534/tuprints-00009485
Ph.D. Thesis, Primary publication
|
Text
dissertation_jahn_v2.pdf Copyright Information: CC BY-NC-ND 4.0 International - Creative Commons, Attribution NonCommercial, NoDerivs. Download (3MB) | Preview |
Item Type: | Ph.D. Thesis | ||||
---|---|---|---|---|---|
Type of entry: | Primary publication | ||||
Title: | The Topological Susceptibility of QCD at High Temperatures | ||||
Language: | English | ||||
Referees: | Moore, Prof. PhD Guy D. ; Braun, Prof. Dr. Jens | ||||
Date: | 27 November 2019 | ||||
Place of Publication: | Darmstadt | ||||
Date of oral examination: | 27 November 2019 | ||||
DOI: | 10.25534/tuprints-00009485 | ||||
Abstract: | Two of the most challenging problems in modern physics are the origin of dark matter and the strong CP problem. The latter means the non-observation of the violation of the combined particle-antiparticle and parity (CP) symmetries by the strong interaction which is conceptually allowed. Both problems - although prima facie disparate - could be simultaneously solved by the Peccei-Quinn mechanism. This results in a new particle, the axion. Despite strong experimental efforts, the discovery of the axion is yet to come, making precise theoretical predictions of its properties, especially its mass, highly valuable. The axion's properties are closely related to the topological structure of the vacuum of quantum chromodynamics (QCD). The QCD vacuum exhibits topologically non-trivial fluctuations of the gauge fields with the most important fluctuations being instantons. These topological fluctuations are quantified by the topological susceptibility that controls the axion mass and therefore is - especially at high temperatures - an important input for axion cosmology. Since topological effects are inherently non-perturbative, lattice QCD is particularly suitable for precisely determining the topological susceptibility. However, lattice simulations become extremely challenging at high temperatures because the topological susceptibility is very suppressed. In this work, we develop and establish a novel method based on a combination of gradient flow and reweighting that artificially enhances the number of instantons and therefore allows to determine the topological susceptibility at high temperatures. For computational simplicity, we content ourselves to pure SU(3) Yang-Mills theory for developing the method, but it is explicitly designed to be applicable also in full QCD. In particular, we provide a discretization of the instanton that allows for an analysis of the lattice-spacing effects on a lattice study of the topological susceptibility. We then present the reweighting method that is eventually used to determine the topological susceptibility up to 2 GeV in pure SU(3) Yang-Mills theory which constitutes the first direct determination of the topological susceptibility at such high temperatures. |
||||
Alternative Abstract: |
|
||||
URN: | urn:nbn:de:tuda-tuprints-94854 | ||||
Classification DDC: | 500 Science and mathematics > 530 Physics | ||||
Divisions: | 05 Department of Physics > Institute of Nuclear Physics > Theoretische Kernphysik > Kerne und Materie an den Extremen 05 Department of Physics > Institute of Nuclear Physics > Theoretische Kernphysik > Quanten-Chromo-Dynamic |
||||
Date Deposited: | 17 Dec 2019 12:00 | ||||
Last Modified: | 17 Dec 2019 12:00 | ||||
URI: | https://tuprints.ulb.tu-darmstadt.de/id/eprint/9485 | ||||
PPN: | 457523093 | ||||
Export: |
View Item |