HTL Self-energies in Hot and Dense QCD

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Title: HTL Self-energies in Hot and Dense QCD
Author: Seppänen, Kaapo
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2021
Language: eng
Thesis level: master's thesis
Degree program: Teoreettisten ja laskennallisten menetelmien maisteriohjelma (Theoretical Calculation Methods)
Master 's Programme in Theoretical and Computational Methods
Magisterprogrammet i teoretiska och beräkningsmetoder
Specialisation: Teoreettinen fysiikka
Theoretical Physics
Teoretisk fysik
Abstract: We determine the leading thermal contributions to various self-energies in finite-temperature and -density quantum chromodynamics (QCD). The so-called hard thermal loop (HTL) self-energies are calculated for the quark and gluon fields at one-loop order and for the photon field at two-loop order using the real-time formulation of thermal field theory. In-medium screening effects arising at long wavelengths necessitate the reorganization of perturbative series of thermodynamic quantities. Our results may be directly applied in a reorganization called the HTL resummation, which applies an effective theory for the long-wavelength modes in the medium. The photonic result provides a partial next-to-leading order correction to the current leading-order result and can be later extended to pure QCD with the techniques we develop. The thesis is organized as follows. First, by considering a complex scalar field, we review the main aspects of the equilibrium real-time formalism to build a solid foundation for our thermal field theoretic calculations. Then, these concepts are generalized to QCD, and the properties of the QCD self-energies are thoroughly studied. We discuss the long-wavelength collective behavior of thermal QCD and introduce the HTL theory, outlining also the main motivations for our calculations. The explicit computations of self-energies are presented in extensive detail to highlight the computational techniques we employ.
Subject: quantum chromodynamics
thermal field theory
real-time formalism
perturbation theory

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