Maximally twisted mass lattice QCD at the physical pion mass
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Department
Mathematisch-Naturwissenschaftliche Fakultät
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Abstract
In der Gitterquantenchromodynamik sind der Einsatz von unphysikalisch großen Quarkmassen und die Extrapolation von Ergebnissen zu physikalischen Massen signifikante systematische Fehlerquellen. In dieser Arbeit wird die praktische Durchführbarkeit numerischer Simulationen der Quantenchromodynamik mit physikalisch leichten up und down Quarkmassen unter Verwendung der Wilson twisted mass Diskretisierung untersucht. Simulationen im Regime physikalisch leichter Quarkmassen sind jedoch einerseits numerisch sehr aufwendig, können andererseits aber auch durch das Auftreten großer Diskretisierungsartefakte nicht praktikabel sein. Anhand von Simulationen mit massendegenerierten dynamischen up und down Quarks wird dargestellt dass die Erweiterung der twisted mass Fermionwirkung durch den Sheikholeslami-Wohlert Term es ermöglicht physikalisch leichte Quarkmassen zu erreichen. Es wird gezeigt, dass die Simulationen stabil sind und dass die Parameter der diskretisierten Theorie so gewählt werden können, dass das geladene Pion seine physikalische Masse annimmt. Ferner wird dargestellt, dass auch die Parameter für eine Simulation mit dynamischen massendegenerierten up und down quarks sowie nichtdegenerierten strange und charm Quarks schrittweise auf ihre physkalischen Werte gesetzt werden können. Um das Verhalten von Observablen bei physikalischer Quarkmasse zu untersuchen, werden Massen und Zerfallskonstanten von pseudoskalaren Mesonen mit up, down sowie strange und charm Valenzquarks berechnet. Die Ergebnisse stimmen größtenteils überein mit den phänomenologischen Werten, obwohl weder Kontinuumslimes noch die Extrapolation zu unendlichem Volumen durchgeführt werden. Renormierte leichte, strange und charm Quarkmassen werden über Interpolationen in hadronischen Observablen berechnet und stimmen ebenso größtenteils mit phänomenologischen Werten und anderen Ergebnissen aus der Gitter-QCD überein.
In computer simulations of Lattice Quantum Chromodynamics, the usage of unphysically large quark masses and the subsequent extrapolation of results to the physical value of the quark masses are major sources of systematic uncertainty. In this thesis, the feasibility and practicality of numerical simulations of Quantum Chromodynamics with physically light up and down quarks using the Wilson twisted mass quark discretisation are explored. Working in this regime is complicated firstly by the numerical expense of these simulations and secondly by the presence of potentially large lattice artefacts. The twisted mass discretisation is affected by an unphysical mass difference between the charged and neutral pions, rendering simulations at the physical charged pion mass infeasible if this mass splitting is too large. With the aim of reducing it, the Sheikholeslami-Wohlert term is added to the twisted mass fermion action and simulations with mass degenerate up and down quarks are then performed as a proof of concept. It is demonstrated that these simulations are stable and that the parameters of the lattice theory can be successfully tuned to correspond to the physical charged pion mass. Subsequently, the parameter tuning for simulations with mass degenerate up and down quarks as well as strange and charm quarks is explored and it is shown that it can be carried out in steps. As benchmark observables, the masses and decay constants of pseudoscalar mesons with light, strange and charm valence quarks are calculated and seen to largely reproduce their phenomenological values, even though continuum and infinite volume extrapolations are not performed. Light, strange and charm quark mass estimates are determined based on this data and also seen to coincide with phenomenological and other lattice determinations.
In computer simulations of Lattice Quantum Chromodynamics, the usage of unphysically large quark masses and the subsequent extrapolation of results to the physical value of the quark masses are major sources of systematic uncertainty. In this thesis, the feasibility and practicality of numerical simulations of Quantum Chromodynamics with physically light up and down quarks using the Wilson twisted mass quark discretisation are explored. Working in this regime is complicated firstly by the numerical expense of these simulations and secondly by the presence of potentially large lattice artefacts. The twisted mass discretisation is affected by an unphysical mass difference between the charged and neutral pions, rendering simulations at the physical charged pion mass infeasible if this mass splitting is too large. With the aim of reducing it, the Sheikholeslami-Wohlert term is added to the twisted mass fermion action and simulations with mass degenerate up and down quarks are then performed as a proof of concept. It is demonstrated that these simulations are stable and that the parameters of the lattice theory can be successfully tuned to correspond to the physical charged pion mass. Subsequently, the parameter tuning for simulations with mass degenerate up and down quarks as well as strange and charm quarks is explored and it is shown that it can be carried out in steps. As benchmark observables, the masses and decay constants of pseudoscalar mesons with light, strange and charm valence quarks are calculated and seen to largely reproduce their phenomenological values, even though continuum and infinite volume extrapolations are not performed. Light, strange and charm quark mass estimates are determined based on this data and also seen to coincide with phenomenological and other lattice determinations.
Description
Keywords
Gitter-QCD, Hochgeschwidigkeitsrechnen, nicht-perturbativ, Quantenchromodynamik, Meson, Hadron, Zerfallskonstante, Lattice-QCD, high performance computing, non-perturbative, quantum-chromo-dynamics, meson, hadron, decay constant
Dewey Decimal Classification
530 Physik
Citation
Kostrzewa, Bartosz.(2017). Maximally twisted mass lattice QCD at the physical pion mass. 10.18452/17733