Rozprawy doktorskie: „Finite temperature QCD”

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Cossu, Guido. "Deconfinement transition in QCD at finite temperature". Doctoral thesis, Scuola Normale Superiore, 2009. http://hdl.handle.net/11384/85831.

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The main subject of this thesis is the problem of confinement in QCD. Since the discovery of quarks in high energy experiments, their absence as free particles in nature became one of the hot topics in modern physics. The non abelian gauge field theories developed in the 50s by Yang and Mills and successively generalized in the Standard Model have proved successful in describing the real world. Electroweak and short distance interactions are well explained by perturbative expansions in gauge coupling powers. Perturbative calculations, however, cannot account for the confinement problem which is inherently non perturbative in nature. The non perturbative region of strongly coupled theories was out of reach for any analytical calculation since the proposal by Wilson of a regularization on the lattice of gauge field theories. Soon, in early works of lattice field theory it was realized that Yang Mills theories could also account for confinement of quarks by a potential linearly rising with distance. In finite temperature calculations it was also shown that this linear behavior disappears as some temperature Tc , called deconfinement temperature, above which quarks are not bounded inside hadrons. At present time there are no widely accepted explanations from first principles of the dynamics of confinement. Several mechanisms were proposed to describe confinement at low temperatures by means of the topological properties of Yang Mills theories. We shall concentrate on the so called Dual Superconductor Picture which conjectures that confinement is related to condensation of magnetic charges in analogy with common superconductors where condensation of electric charges “confines” magnetic monopoles. We shall propose and test a way to prove its correctness in several gauge theories (see chapter 3). Although no definitive conclusions can be drawn, we shall show, by using an operator that detects the condensation of magnetic charges in the vacuum, that the Dual Superconductor Picture is indeed a proper candidate for the description of the confinement dynamics. The problem was deeply studied in the last years by the Pisa group. The confinement by condensation of monopoles was demonstrated in an U(1) abelian theory both analytically (Frölich and Marchetti) and numerically (Pisa group). During my PhD we discovered that some of our previous data on non abelian gauge theories were misinterpreted. In pure non abelian gauge theories, the presence of unphysical bulk transitions spoils the relation of the operator singularities to a confinement-deconfinement transition. Conversely, similar calculations in theories with fermions in different representations do not show any signal of bulk transitions and results are consistent with the Dual Superconductor Picture. We are dedicating our efforts to clarify this unwelcome behavior of the operator. I will present the first attempts to redefine the operator in pure gauge theories to circumvent these issues. The problem of a suitable definition of the operator on the lattice is still open and a detailed discussion on the subject will be proposed in chapter 3. If the confinement-deconfinement transition is related to the breaking of some symmetry of the theory we then expect that a true phase transition takes place. Strictly speaking, we have explicit symmetries only in the two opposite regions of zero and infinite quark masses (respectively chiral and center symmetries). We aim at establishing if, even at finite quark masses, the path from the low temperature region (confined) to the high temperature region where quarks are free, encounters singularities. A positive answer demonstrates the non trivial fact this two phases have different symmetries, otherwise confinement is ambiguously defined. In this respect, the problem of determining the order of the chiral transition in QCD with two degenerate quarks, a case close to the physical one, becomes a relevant point (chapter 4). In few words, if the transition is second order for massless quarks we then expect that it turns into a crossover for light masses, while if the transition is first order then the non analyticity could survive in a region of small masses (or beyond). The later possibility could explain naturally the experimental evidence of free quark suppression in nature. In chapter 4 we shall address the problem with Finite Size Scaling techniques (chapter 2). By isolating the dependence on one of the two variables (temperature and bare quark mass) we shall analyze the volume scaling of thermodynamical quantities like specific heat and chiral condensate susceptibility. The task of unambiguously determining the order is hard to accomplish but we shall give some evidences that, despite the common lore, the transition could be first order, and that surely is not second order in the class predicted by effective theories. Summarizing the objectives of this thesis is twofold: • address the confinement problem by probing the vacuum with a magnetically charged operator to establish if the dual superconductor picture is a valid picture; • address the confinement problem by studying the related issue of the order of the transition in two flavors quantum chromodynamics.

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Zhang, Yingwen. "Applications of QCD sum rules at finite temperature". Doctoral thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/30179.

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QCD Sum Rules is one of the most successful quantum field theory frameworks to extract hadronic information from QCD analytically. This technique is based on the Operator Product Expansion (OPE) and Cauchy's Theorem in the complex energy plane. OPE factorizes the short and long distance interactions where the former are calculated using perturbative theory, and the latter are parameterized in terms of the quark and gluon vacuum condensates. By using Cauchy's theorem, the results from QCD calculations can be matched to the hadronic channel, this is known as 'quark-hadron duality'. My Project involves using QCD Sum Rules to determine the behaviour of hadronic parameters of charmonium in the scalar and pseudoscalar channel and also light-light quark mesons in the vector and axial-vector channel at finite temperature. From our results of the behaviour of the width and the hadronic coupling at finite temperature, both channels of charmonium shows signs of survival beyond the deconfinement temperature Tc whereas the light-light quark mesons disappears at Tc. An extension of the method to finite density in. the axial-vector channel of light-light quark mesons also shows signs of disappearance at the deconfinement density μc.

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Hatta, Yoshitaka. "The QCD phase transition at finite temperature and density". 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147809.

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Aouane, Rafik. "Gluon and ghost propagator studies in lattice QCD at finite temperature". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16735.

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Die im infraroten Impulsbereich der Quantenchromodynamik (QCD) berechneten Gluon- und Ghost-Propagatoren spielen eine große Rolle für das sogenannte Confinement der Quarks und Gluonen. Sie sind Gegenstand intensiver Foschungen dank nicht-perturbativer Methoden basierend auf Dyson-Schwinger- (DS) und funktionalen Renormierungsgruppen-Gleichungen (FRG). Darüber hinaus sollte es deren Verhalten bei endlichen Temperaturen erlauben, den chiralen und Deconfinement-Phasenübergang bzw. das Crossover in der QCD besser aufzuklären. Unser Zugang beruht auf der gitter-diskretisierten QCD (LQCD), die es als ab-initio-Methode gestattet, verschiedenste störungstheoretisch nicht zugängliche QCD-Observablen der hadronischen Welt zu berechnen. Wir untersuchen das Temperaturverhalten der Gluon- und Ghost-Propagatoren in der Landau-Eichung für die reine Gluodynamik und die volle QCD. Für den Gluon-Propagator berechnen wir deren longitudinale (DL) sowie transversale (DT) Komponenten. Ziel ist es, Datensätze in Form von Fit-Formeln zu liefern, welche als Input für die DS- (oder FRG-) Gleichungen verwendet werden können. Wir beschäftigen uns mit der vollen (Nf=2) LQCD unter Verwendung der sogenannten twisted mass Fermiondiskretisierung. Von der tmfT-Kollaboration wurden uns dafür Eichfeldkonfigurationen für Temperaturen im Crossover-Bereich sowie jeweils für drei fixierte Pion-Massenwerte im Intervall [300, 500] MeV bereitgestellt. Schließlich berechnen wir innerhalb der reinen SU(3) Eichtheorie (bei T=0) den Landau Gluon-Propagator unter Verwendung verschiedener Eichfixierungskriterien. Unser Ziel ist es, den Einfluss von Eich-Kopien mit minimalen (nicht-trivialen) Eigenwerten des Faddeev-Popov-Operators zu verstehen. Eine solche Studie soll klären, wie Gribov-Kopien das Verhalten der Gluon- und Ghost-Propagatoren im infraroten Bereich prinzipiell beeinflussen.
Gluon and ghost propagators in quantum chromodynamics (QCD) computed in the infrared momentum region play an important role to understand quark and gluon confinement. They are the subject of intensive research thanks to non-perturbative methods based on Dyson-Schwinger (DS) and functional renormalization group (FRG) equations. Moreover, their temperature behavior might also help to explore the chiral and deconfinement phase transition or crossover within QCD at non-zero temperature. Our prime tool is the lattice discretized QCD (LQCD) providing a unique ab-initio non-perturbative approach to deal with the computation of various observables of the hadronic world. We investigate the temperature dependence of Landau gauge gluon and ghost propagators in pure gluodynamics and in full QCD. Regarding the gluon propagator, we compute its longitudinal DL as well its transversal DT components. The aim is to provide a data set in terms of fitting formulae which can be used as input for DS (or FRG) equations. We deal with full (Nf=2) LQCD with the twisted mass fermion discretization. We employ gauge field configurations provided by the tmfT collaboration for temperatures in the crossover region and for three fixed pion mass values in the range [300,500] MeV. Finally, within SU(3) pure gauge theory (at T=0) we compute the Landau gauge gluon propagator according to different gauge fixing criteria. Our goal is to understand the influence of gauge copies with minimal (non-trivial) eigenvalues of the Faddeev-Popov operator.

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Fetea, Mirela Simona. "Pions and vector mesons at finite temperature from QCD sum rules". Doctoral thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/9694.

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Bibliography: p. 89-92.
The temperature corrections to the current algebra Gell-Mann, Oakes and Renner(GMOR) relation in SU(2) X SU(2), the temperature behaviour of the pion mass and the q2 and T dependence of the ρππ vertex function in the space-like region are investigated.

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Vuorinen, Aleksi. "The pressure of QCD at finite temperature and quark number density". Helsinki : University of Helsinki, 2003. http://ethesis.helsinki.fi/julkaisut/mat/fysik/vk/vuorinen/.

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Burger, Florian. "The finite temperature QCD phase transition and the thermodynamic equation of state". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16679.

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In dieser Arbeit wird mit Hilfe der Gitter-Methode der Phasenübergang/Crossover bei nicht verschwindender Temperatur der Quantenchromodynamik mit zwei Quark Flavour untersucht sowie die thermodynamische Zustandsgleichung berechnet. Es wird dabei die Wilson twisted-mass Formulierung der Quark-Wirkung verwendet, welche hinsichtlich des Kontinuum-Limes eine automatische Verbesserung birgt. Erste belastbare Resultate mit dieser Wirkung bei endlicher Temperatur werden in dieser Arbeit gezeigt. Mehrere kleine Werte der Pion-Masse werden betrachtet mit dem Ziel, Aufschluss über die Ordnung des Phasenüberganges im chiralen Limes zu erhalten. Im Bereich der von uns simulierten Pion-Massen zwischen 300 und 700 MeV wird hierbei lediglich ein Crossover-Übergang beobachtet. Die Abhängigkeit der gemessenen Crossover-Temperatur von der Masse wird für eine Extrapolation zu verschwindender Masse hin verwendet unter der Annahme verschiedener Szenarien für den chiralen Limes. Dazu komplementär wird das chirale Kondensat, der Ordnungsparameter der spontanen Brechung der chiralen Symmetrie, vor dem Hintergrund der so genannten magnetischen Zustandsgleichung untersucht, welche das universelle Verhalten in der Nähe des Phasenüberganges für die Universalitätsklasse des O(4) Modells angibt. Hinsichtlich der Thermodynamik wird ausgehend von der Spur-Anomalie und unter Benutzung der Temperatur-Integral Methode der Druck und die Energiedichte im Crossover-Gebiet berechnet. Der Kontinuum-Limes der Spur-Anomalie wird mit mehreren Gitterdiskretisierungen der Temperatur Nt sowie unter Zuhilfenahme einer tree-level Korrektur untersucht.
In this thesis we report about an investigation of the finite temperature crossover/phase transition of quantum chromodynamics and the evaluation of the thermodynamic equation of state. To this end the lattice method and the Wilson twisted mass discretisation of the quark action are used. This formulation is known to have an automatic improvement of lattice artifacts and thus an improved continuum limit behaviour. This work presents first robust results using this action for the non-vanishing temperature case. We investigate the chiral limit of the two flavour phase transition with several small values of the pion mass in order to address the open question of the order of the transition in the limit of vanishing quark mass. For the currently simulated pion masses in the range of 300 to 700 MeV we present evidence that the finite temperature transition is a crossover transition rather than a genuine phase transition. The chiral limit is investigated by comparing the scaling of the observed crossover temperature with the mass including several possible scenarios. Complementary to this approach the chiral condensate as the order parameter for the spontaneous breaking of chiral symmetry is analysed in comparison with the O(4) universal scaling function which characterises a second order transition. With respect to thermodynamics the equation of state is obtained from the trace anomaly employing the temperature integral method which provides the pressure and energy density in the crossover region. The continuum limit of the trace anomaly is studied by considering several values of Nt and the tree-level correction technique.

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Robaina, Fernandez Daniel [Verfasser]. "Static and dynamic properties of QCD at finite temperature / Daniel Robaina Fernandez". Mainz : Universitätsbibliothek Mainz, 2016. http://d-nb.info/1106573382/34.

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Oevers, Manfred [Verfasser]. "The finite temperature phase diagram of 2-flavour QCD with improved Wilson fermions / Manfred Oevers". Bielefeld : Universitätsbibliothek Bielefeld, 1999. http://d-nb.info/1034401254/34.

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Heide, Johannes van der. "The pion form factor from lattice QCD a non-perturbative study at zero and finite temperature /". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/76697.

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Pinke, Christopher [Verfasser], Owe Akademischer Betreuer] Philipsen, Hartmut [Akademischer Betreuer] [Wittig i Luciano [Akademischer Betreuer] Rezzolla. "Lattice QCD at finite temperature with Wilson fermions / Christopher Pinke. Gutachter: Owe Philipsen ; Hartmut Wittig ; Luciano Rezzolla. Betreuer: Owe Philipsen". Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2014. http://d-nb.info/1058626027/34.

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Ghiglieri, Jacopo [Verfasser], Nora [Akademischer Betreuer] Brambilla i Wolfram [Akademischer Betreuer] Weise. "Effective Field Theories of QCD for Heavy Quarkonia at Finite Temperature / Jacopo Ghiglieri. Gutachter: Nora Brambilla ; Wolfram Weise. Betreuer: Nora Brambilla". München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/101486139X/34.

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Aouane, Rafik [Verfasser], Michael [Akademischer Betreuer] Müller-Preußker, Christian [Akademischer Betreuer] Fischer i Ernst-Michael [Akademischer Betreuer] Ilgenfritz. "Gluon and ghost propagator studies in lattice QCD at finite temperature / Rafik Aouane. Gutachter: Michael Müller-Preußker ; Christian Fischer ; Ernst-Michael Ilgenfritz". Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://d-nb.info/1034865595/34.

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Niblaeus, Carl. "In-medium width of the η' meson". Thesis, Uppsala universitet, Kärnfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-210687.

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In this master’s thesis the width of the $\eta'$ meson is studied as a function of temperature. We consider a background medium consisting of a pion gas and assume a vanishing net baryon chemical potential. The width is obtained in the framework of large $N_{c}$ chiral perturbation theory and we consider terms up to next-to-leading order in the effective Lagrangian. We use a low-density approximation to calculate the width increase due to scattering with pions from the heat bath. The results suggest that the in-medium width for the $\eta'$ may become of considerable size: at a temperature $T\approx 75$ MeV we find a width increase of $\Delta\Gamma\approx 3-4$ MeV, comparable to the inverse lifetime of the fireball created in a heavy-ion collision. The $\eta'$ is of particular interested since it is intimately connected to the $U(1)_{A}$ anomaly of Quantum Chromodynamics (QCD). It has been speculated that $U(1)_{A}$ may become a symmetry of QCD at high temperatures and studies of the $\eta'$ could indicate if that is the case. Depending on for how large temperatures the results from large $N_{c}$ can be trusted, they indicate that the $\eta'$ may be possible to study experimentally in heavy-ion collisions due to its sizable in-medium width.

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Glesaaen, Jonas Rylund [Verfasser], Owe [Akademischer Betreuer] [Gutachter] Philipsen i Dirk-Hermann [Gutachter] Rischke. "Heavy quark QCD at finite temperature and density using an effective theory / Jonas Rylund Glesaaen ; Gutachter: Owe Philipsen, Dirk-Hermann Rischke ; Betreuer: Owe Philipsen". Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2017. http://d-nb.info/1129254267/34.

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Burger, Florian [Verfasser], Michael [Akademischer Betreuer] Müller-Preußker, Maria-Paola [Akademischer Betreuer] Lombardo i Edwin [Akademischer Betreuer] Laermann. "The finite temperature QCD phase transition and the thermodynamic equation of state : an investigation employing lattice QCD with N f = 2 twisted mass quarks / Florian Burger. Gutachter: Michael Müller-Preußker ; Maria-Paola Lombardo ; Edwin Laermann". Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://d-nb.info/1031956018/34.

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Berwein, Matthias Wilhelm Georg [Verfasser], Nora [Akademischer Betreuer] [Gutachter] Brambilla, Eric [Gutachter] Braaten i Norbert [Gutachter] Kaiser. "Heavy Quark-Antiquark Pairs at Zero and Finite Temperature with Effective Field Theories of QCD / Matthias Wilhelm Georg Berwein ; Gutachter: Nora Brambilla, Eric Braaten, Norbert Kaiser ; Betreuer: Nora Brambilla". München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1119319161/34.

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Frigori, Rafael Bertolini. "Estudo numérico da transição de fase na QCD a temperatura finita". Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-12112007-090407/.

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Em nossas simulações, efetuamos uma cuidadosa análise numérica dos algoritmos de Monte Carlos empregados na termalização de teorias de gauge e sistemas de spins contínuos. Dentre eles, apresentamos uma nova proposta que permite reduzir em cerca de 25% os tempos computacionais. Aplicamos este novo algoritmo ao estudo numérico da transição de desconfinamento da teoria de Yang-Mills (YM) SU(2) tridimensional, a temperatura finita, em redes com volumes de 502 X 4 sítios. Por fim, também utilizamos técnicas de Escala de tamanho finito (FSS), Dinâmica de Tempos Curtos e Métodos Variacionais para extrair os expoentes críticos e espectro de massas de blindagem desta teoria.
In our numerical simulations, we have done a careful analysis of Monte-Carlo algorithms usually applied in the thermalization of gauge theories and continuous-spin systems. Among them we present a new proposal that enables a reduction of roughly 25% in the computational time. We apply this new algorithm to a numerical study of the at finite temperature, using lattices with 502 x 4 sites. We also use Finite-Size-Scaling techniques, Short-Time Dynamics and Variational Methods to extract critical exponents and the spectrum of screening masses of the theory.

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Pilon, Eric. "Qcd quantitative et photons reels quelques problemes infrarouges en theorie des champs a temperature finie". Paris 11, 1992. http://www.theses.fr/1992PA112162.

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Cette these comprend deux parties distinctes. La premiere concerne l'application quantitative de la chromodynamique quantique (qcd) en physique des hautes energies. Elle contient elle-meme deux volets. Le premier volet porte sur l'importance des corrections qcd d'ordre superieur dans les processus de production a grande impulsion transverse impliquant des photons (quasi) reels. Nos travaux concernent tout d'abord la photoproduction de photons directs au collisionneur electro-proton hera de hamburg, ou nous montrons l'importance des corrections d'ordre superieur a la contribution de fonction de structure du photon, et la possibilite de mesurer le contenu en gluons du photon initial. Nous etudions egalement les corrections d'ordre superieur a la composante de bremmstrahlung dans la hadroproduction de photons directs aux collisionneurs sps du cern et tevatron de fermilab et mesurable aux supercollisionneurs futurs lhc et ssc, en mettant en evidence la predominance de la fragmentation inclusive de gluons en photons en debut de spectre. Le second volet expose une approche semi numerique au traitement des corrections qcd d'ordre superieur, visant a incorporer de facon quantitative l'hadronisation de l'etat final partonique. Nous analysons les problemes poses par le mariage d'un calcul d'ordre superieur au niveau partonique avec le branchement de l'hadronisation complete a la lund. La seconde partie presente deux travaux consacres a l'etude de quelques problemes infrarouges en theorie des champs a temperature finie. Nous analysons la possible extension du theoreme de kinoshita, lee-nauenberg a temperature finie sur l'exemple du taux de conversion neutron-proton, et montrons la compensation des singularites colineaires et soft au premier ordre dans la constante de structure fine. Puis nous analysons l'anomalie axiale a temperature finie par l'approche dispersive de dolgov-zakharov sur l'exemple du modele de schwinger, et mettons en evidence le mecanisme de compensation des contributions thermiques qui aboutit a l'independance de l'anomalie axiale vis-a-vis de la temperature

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Antunes, Sérgio M. [UNESP]. "Estudo de sistemas hadrônicos no limite de acoplamento forte da QCD: simetria quiral a densidades e temperaturas finitas". Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/132749.

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Antunes, Sérgio M. "Estudo de sistemas hadrônicos no limite de acoplamento forte da QCD: simetria quiral a densidades e temperaturas finitas /". São Paulo, 2009. http://hdl.handle.net/11449/132749.

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Orientador: Gastão Inácio Krein
Banca: Rudnei de Oliveira Ramos
Banca: Heron Carlos de Godói Caldas
Banca: Sérgio Szpigel
Banca: Sandra dos Santos Padula
Resumo: Desenvolvemos um formalismo para estudar a quebra dinâmica da simetria quiral na matéria hadrônica em que os quarks e gluons estão confinados no interior dos hádrons. O formalismo emprega as técnicas tradicionais da teoria quântica de muitos corpos em conjunção com a representação Fock-Tani, em que os estados ligados hadrônicos são descritos em termos de operadores de campos que satisfazem regras de comutação canônicas em um espaço de Fock estendido. Empregamos um modelo de quarks inspirado na Hamiltoniana da QCD no calibre de Coulomb que confina quarks e gluons e realiza a quebra dinâmica da simetria quiral. Resultados numéricos foram obtidos para a equação de gap para os quarks num meio hadrônico formado por nucleons a temperatura zero. Como aplicação do formalismo estimamos os efeitos da densidade bariônica sobre o potencial de interação entre mésons charmosos D com nucleons obtido com a representação Fock-Tani dentro do mesmo modelo de quarks
Abstract: We have developed a formalism to study dynamical chiral symmetry breaking in hadronic matter where quarks and gluons are confined within hadrons. The for- malism employs the traditional techniques of the quantum many body theory in conjunction with the Fock-Tani representation in which the hadronic bound States are described in terms of field operators that satisfy canonical commutation rela- tions in an extended Fock space. We have employed a quark model inspired in the QCD Hamiltonian in Coulomb gauge that confines quarks and gluons and realizes dynamical chiral symmetry breaking. Numerical results are obtained for the gap equation in a hadronic médium formed by nucleons at zero temperature. As an application of the formalism we have estimated the effects of the barionic density on the interaction potential of charmed D mesons with nucleons obtained with the Fock-Tani representation within the the same quark model
Doutor

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Costa, Ricardo de Souza. "Estudo do espectro das massas de blingagem de cor em QDC na rede a temperatura finita". Universidade do Estado do Rio de Janeiro, 2008. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=1207.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Neste trabalho estudamos o espectro das massas de blindagem mais baixas em teorias do tipo Yang_Mills na rede.Utilizamos os grupos de calibre SU(2) e SU(3) em 2+1 e 3+1 dimensões. Os cálculos foram realizados perto da temperatura crítica da transição de fase confinamento-desconfinamento. Obtivemos valores para as razôes entre as massas consistentes com os valores previstos a partir de universidade.
In this work we study the spectrum of the lowest screening masses for Yang-Mills theories on the lattice. We used the gauge groups SU(2) and SU(3) in 2 + 1 and 3 + 1 dimensions. Calculations were done near the critical temperature of the confinement-desconfinement phase transition. We obtained values for the ratios of the screening masses consistent with predictions from universality arguments.

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Costa, Lúcio Campos [UNESP]. "Estudo da violação das simetrias de Lorentz e CPT na eletrodinâmica quântica". Universidade Estadual Paulista (UNESP), 2004. http://hdl.handle.net/11449/102501.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Na presente tese, investiga-se uma versão estendida da eletrodinâmica quântica, onde se introduz um termo de acoplamento axial renormalizável não invariante, dando ênfase à quebra dinâmica das simetrias de Lorentz e CPT no setor de gauge e à ambigüidade no coeficiente do termo do tipo Chern-Simons, induzido através de correções radiativas e outros métodos não perturbativos. Aspectos da teoria efetiva de Euler-Kockel-Heisenberg a tempertura finita também são investigados à luz do formalismo conhecido como Thermo Field Dynamics.
In the present thesis it is investigated an extended version of quantum electrodynamic where a renormalized non-invariant axial coupling term introduced, emphasizing the dynamic violation of the Lorentz and CPT symmetries in the gauge sector of the theory as well as the ambiguity of the coeficient of the Chern-Simon-like term, induced through radiative corrections and other non-perturbative methods. Some aspects of the Euler-Kockel-Heisenber effective theory at finite temperature have also been addressed in the context of the Thermo Field Dynamics formalism.

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Müller, Jens Andreas. "A Dyson-Schwinger Approach to Finite Temperature QCD". Phd thesis, 2011. http://tuprints.ulb.tu-darmstadt.de/2395/1/diss_main.pdf.

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The different phases of quantum chromodynamics at finite temperature are studied. To this end the nonperturbative quark propagator in Matsubara formalism is determined from its equation of motion, the Dyson-Schwinger equation. A novel truncation scheme is introduced including the nonperturbative, temperature dependent gluon propagator as extracted from lattice gauge theory. In the first part of the thesis a deconfinement order parameter, the dual condensate, and the critical temperature are determined from the dependence of the quark propagator on the temporal boundary conditions. The chiral transition is investigated by means of the quark condensate as order parameter. In addition differences in the chiral and deconfinement transition between gauge groups SU(2) and SU(3) are explored. In the following the quenched quark propagator is studied with respect to a possible spectral representation at finite temperature. In doing so, the quark propagator turns out to possess different analytic properties below and above the deconfinement transition. This result motivates the consideration of an alternative deconfinement order parameter signaling positivity violations of the spectral function. A criterion for positivity violations of the spectral function based on the curvature of the Schwinger function is derived. Using a variety of ansätze for the spectral function, the possible quasi-particle spectrum is analyzed, in particular its quark mass and momentum dependence. The results motivate a more direct determination of the spectral function in the framework of Dyson-Schwinger equations. In the two subsequent chapters extensions of the truncation scheme are considered. The influence of dynamical quark degrees of freedom on the chiral and deconfinement transition is investigated. This serves as a first step towards a complete self-consistent consideration of dynamical quarks and the extension to finite chemical potential. The goodness of the truncation is verified first at vanishing chemical potential. Interestingly, besides good agreement of the transition temperatures with lattice QCD calculations, the different deconfinement criteria of the dual condensate and of the Schwinger-function yield similar results. In the following, the effects of a finite quark chemical potential are studied. These calculations allow for a first insight on the dual condensate at finite chemical potential beyond mean-field calculations in phenomenological models. In addition, a possibility to include the back-reaction of long-range fluctuations in the vicinity of a second order phase transition is elaborated. In the scaling region constraints for a self-consistent solution arise from an analytic investigation.

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25

Liu, Kun-Min, i 劉崑民. "Monte Carlo Simulation of Quenched QCD at Finite Temperature". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23216749742412852511.

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碩士
國立臺灣大學
物理研究所
99
In this thesis, we study the finite temperature phase transition of the pure SU(3) gauge theory. We use the hybrid Monte Carlo method to simulate the quenched QCD at finite temperature, with Wilson gauge action on the 16^3 × 6 lattice. From the Polyakov loop and its susceptibility, we determine the value of the critical temperature Tc = 274 ± 1 MeV, in agreement with the widely accepted value of Tc ~ 270 MeV for pure SU(3) gauge theory.

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26

Kwon, Youngshin [Verfasser]. "QCD sum rule studies at finite density and temperature / Youngshin Kwon". 2009. http://d-nb.info/1000455432/34.

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27

Müller, Jens Andreas [Verfasser]. "A Dyson-Schwinger approach to finite temperature QCD / von Jens Andreas Müller". 2011. http://d-nb.info/1010056522/34.

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28

Thakkar, Rishabh. "Mesonic screening mass at zero and finite chemical potential". Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5980.

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The finite temperature analysis of QCD is challenging since perturbation theory is not applicable in that regime. A non-perturbative method like lattice QCD is thus required to obtain an estimate of the necessary observables. In this Ph.D. thesis, we study the symmetries of the chiral phase transition and its transition temperature. This is undertaken by measuring the screening masses of those mesons that rotate amongst themselves under the symmetries. Firstly, we discuss the regime of zero chemical potential where it is easy to obtain the correlators using which we calculate the meson screening masses. We discuss the different computational techniques used for calculating the screening masses on lattice following which we do their continuum extrapolate, to obtain their physical values. Using them, we notice the temperatures at which the symmetries get restored. Finally, we expand our analysis to finite chemical potential. Including the non-zero value of chemical potential to the action makes it imaginary resulting in what is called the sign problem. This imaginary action cannot be used to simulate the system on a lattice. We avoid this problem by expanding the screening correlators in a Taylor series expansion in our analysis. Thus, this gives us an estimate of the screening mass at a small finite chemical potential.

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29

Ding, Heng-Tong [Verfasser]. "Charmonium correlation and spectral functions in quenched lattice QCD at finite temperature / vorgelegt von Heng-Tong Ding". 2010. http://d-nb.info/1009957759/34.

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