Dynamical quark loops at low energies and in medium

doctoral thesis

• Title (croatian): Dinamičke kvarkovske petlje na niskim energijama i u mediju
• Author: Sanjin Benić
• Mentor: Dubravko Klabučar (mentor)
• Committee member: Davor Horvatić (predsjednik povjerenstva)
• Committee member: Dubravko Klabučar (član povjerenstva)
• Committee member: David Blaschke https://orcid.org/0000-0002-8399-5183 (član povjerenstva)
• Committee member: Dalibor Kekez (član povjerenstva)
• Committee member: Mirko Planinić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2013-12-09, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

We performed a research of dynamical quark loops as a basis for microscopic modelling of low-energy aspects of Quantum Chromodynamics (QCD). Part of research covers the calculation of the anomalous transition of a virtual photon into three pions, within a constituent quark-meson model. We study the possibility of adding the lowest resonances, e. g. the rho and omega mesons. In the second part mesons are built from quark-antiquark loops (Bethe-Salpeter amplitudes). Quark propagators are generated from the associated Dyson-Schwinger gap equation. Research is first focused on the η−η′ complex, which is in direct relationship with the gluonic sector of the theory. Using the Matsubara formalism, the calculation is generalized to finite temperatures, where it is particularly interesting to observe influence of the medium on restoration of U(1)A. Experimental analysis of data from heavy-ion collisions at RHIC requires that the mass of the η′ particle significantly reduces at finite temperature, consequently leading to partial restoration of U(1)A symmetry. Given result is explained by a modification of the Witten-Veneziano relation at finite temperature. General study of quark models at finite temperature and density is a third subject of this research. By calculating the equation of state it is established that covariant quark models suffer from a thermodynamic instability. Inclusion of the Polyakov loop stabilizes the system. Within the non-local Nambu Jona Lasinio model effect of Lorentz symmetry breaking on the phase diagram is investigated. Under certain approximations the hadron dissociation effect is discussed for the π and the σ particle at finite temperature. We have shown that the meson widths for dissociation into quark-antiquark pairs as functions of temperature are extremely sensitive to the particular way the quark-antiquark interaction is introduced.

Abstract (croatian)

Istražili smo dinamičke kvarkovske petlje kao temelja za mikroskopsko modeliranje niskoenergetske kvantne kromodinamike (QCD, od engl. Quantum Chromodynamics). Dio istraživanja pokriva računanje anomalnog prijelaza virtualnog fotona u tri piona, unutar konstituentnog kvarkovskog modela. Izučava se mogućnost doprinosa najnižih rezonanci, kao npr. ρ i ω mezona. U drugom dijelu mezoni se grade iz kvark-antikvark petlji (Bethe-Salpeter amplituda). Kvarkovski propagatori generiraju se iz pripadne Dyson-Schwinger jednadžbe procjepa. U fokusu istraživanja je η−η′ kompleks koji je izravnoj vezi s gluonskim sektorom teorije. Pomoću Matsubarinog formalizma račun se generalizira na konačne temperature, gdje je posebice interesantno promotriti utjecaj medija na obnavljanje U(1)A. Analiza eksperimentalnih rezultata sa sudarivača teških iona na RHIC-u nalaže da se masa η′ čestice znatno reducira na konačnoj temperaturi, što posljedično vodi na djelomičnu restauraciju U(1)A simetrije. Dani rezultat se obrazlaže modifikacijom Witten-Veneziano relacije na konačnoj temperaturi. Generalno izučavanje kvarkovskih modela na konačnoj temperaturi i gustoći je treća stavka ovog istraživanja. Računanjem jednadžbe stanja ustanovljuje se da kovarijantni kvarkovski modeli pate od termodinamičke nestabilnosti. Tek uključenje Polyakovljeve petlje stabilizira sustav. Unutar nelokalnih Nambu–Jona-Lasinio modela efekt lomljenja Lorentzove simetrije na fazni dijagram je istražen. Unutar određenih aproksimacija diskutira se disocijacija hadrona za π i σ česticu na konačnoj temperaturi. Pokazano je da širina mezona za disocijaciju u kvark-antikvark par kao funkcija temperature je izrazito osjetljiva na način na koji se efektivna kvark-antikvark interakcija uvodi u sistem.

• Keywords: quantum chromodynamics; hadron physics; quark models; quark matter; phase diagram
• Keywords (croatian): kvantna kromodinamika; hadronska fizika; kvarkovski model; kvarkovska materija; fazni dijagram
• Language: english
• URN:NBN: urn:nbn:hr:217:984849
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 108 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-23 08:44:50