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De, Asitkumar. « Spontaneous chiral symmetry breaking and fermion mass generation in Lattice field theories / ». The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487591658176323.
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Speer, David [Verfasser]. « Spontaneous symmetry breaking transport : from anomalous response to chiral separation / David Speer. Fakultät für Physik. Abt. Theoretische Physik : Theorie der Kondensierten Materie ». Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2011. http://d-nb.info/1011897105/34.
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Matheson, A. « Chiral symmetry breaking ». Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234997.
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Gautam, Bhavesh. « Effets collectifs des micronageurs dans les cristaux liquides nématiques ». Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0062.
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La thèse se concentre sur les effets collectifs des micro-nageurs dans les cristaux liquides nématiques. En utilisant des simulations de Boltzmann sur réseau, nous étudions un système composé de nageurs sphériques au sein d'un cristal liquide nématique. Nos résultats révèlent que le couplage entre les champs de flux du nageur et l'élasticité cristalline liquide peut déstabiliser l'alignement nématique uniforme. Dans l'espace quasi-2D, nous observons l'émergence d'une instabilité dominée par la flexion avec les propulseurs, ce qui est en accord avec les expériences de bactéries dans des films nématiques minces.Après l'ouverture de la troisième dimension, une rupture spontanée de la symétrie chirale est observée ; l'état nématique uniforme devient instable et se transforme en un état cholestérique-like (chiral), caractérisé par une torsion continue dans le champ directeur. Cela est observé à la fois pour les nageurs propulseurs (extensiles) et les nageurs tracteurs (contractiles). En analysant les déformations dans le champ directeur nématique, l'instabilité dominante est identifiée comme étant la torsion-flexion. Nos simulations démontrent que la dynamique des particules et le directeur nématique sont connectés. Dans l'état chiral, tant les nageurs propulseurs que les nageurs tracteurs présentent des trajectoires hélicoïdales.De plus, des stratégies pour contrôler la dynamique des micro-nageurs sont également étudiées. Motivés par des expériences bactériennes, nous considérons des nageurs de types propulseur et tracteur au sein de motifs nématiques. En accord avec les expériences, nos résultats montrent qu'un propulseur présente une trajectoire circulaire dans une flexion pure et une trajectoire linéaire dans un écart pur. Pour un nageur tracteur, un comportement opposé est observé. Enfin, nous explorons le transport de cargaison de particules colloïdales enchevêtrées par des défauts topologiques. Nos simulations suggèrent que le remplacement d'une colloïde passive par un nageur sphérique n'affecte pas le défaut topologique partagé et fournit une mobilité. La particule active est observée pour se lier à la cargaison via un défaut topologique. Avec un nageur propulseur, nous observons un transport guidé le long du directeur nématique, tandis qu'avec un tracteur, un transport perpendiculaire au directeur nématique est observéThe thesis focuses on the collective effects of microswimmers in nematic liquid crystals. Using lattice Boltzmann simulations, we study a system consisting of spherical swimmers within a nematic liquid crystal. Our findings reveal that coupling between the swimmer flow fields and the liquid crystalline elasticity can destabilize the uniform nematic alignment. In quasi-2D space, we observe the emergence of bend-dominated instability with pushers, which is in agreement with experiments of bacteria in thin nematic films.After opening the 3rd dimension, a spontaneous chiral symmetry breaking is observed; the uniform nematic state becomes unstable and transitions into a cholesteric-like (chiral) state, characterized by a continuous twist in the director field. This is observed for both pusher (extensile) and puller (contractile) swimmers. By analyzing the deformations in the nematic director field, the dominant instability is found to be twist-bend. Our simulations demonstrate that the particle dynamics and nematic director are connected. In the chiral state, both pusher and puller swimmers exhibit helical trajectories.Further, strategies for controlling microswimmer dynamics are also studied. Motivated by bacterial experiments, we consider swimmers of both pusher and puller types within nematic patterns. In agreement with experiments, our findings show that a pusher exhibit circular trajectory in a pure bend and linear trajectory in a pure splay. For a puller swimmer, opposite behavior is observed. Finally, we explore cargo transport of colloidal particles entangled by topological defects. Our simulations suggest that replacing a passive colloid with a spherical swimmer does not affect the shared topological defect and provides motility. The active particle is observed to bind to the cargo via a topological defect. With a pusher swimmer, we observe guided transport along the nematic director, while with a puller, transport is observed to be perpendicular to the nematic director
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Seyedi, Shila Seyedi. « QFT and Spontaneous Symmetry Breaking ». Thesis, Uppsala universitet, Teoretisk fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-425891.
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The aim of this project is to understand the structure of the Standard Model of the particle physics. Therefore quantum field theories (QFT) are studied in the both cases of abelian and non-abelian gauge theories i.e. quantum electrodynamics (QED), quantum chromodynamics (QCD) and electroweak interaction are reviewed. The solution to the mass problem arising in these theories i.e. spontaneous symmetry breaking is also studied.Syftet med detta projekt är att förstå strukturen för partikelfysikens standardmodell. Därför studeras kvantfältsteorier (QFT) i båda fallen av abelska och icke-abelska gaugeteorier, dvs kvantelektrodynamik (QED), kvantkromodynamik (QCD) och elektrosvag växelverkan granskas. Lösningen på massproblemet som uppstår i dessa teorier, dvs. spontant symmetribrott studeras också.
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Sousa, Seixas David de. « Spontaneous symmetry breaking in collective neutrino oscillations ». Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-176278.
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We explore the phenomenon of spontaneous symmetry breaking in the context of collective neutrino flavor oscillations. Namely, we investigate the spontaneous breaking of isotropy in a homogeneous gas of neutrinos and of azimuthal isotropy in the context of core-collapse supernovae. For the homo- geneous gas, a simple one-dimensional model is analysed in order to demonstrate the phenomenon and understand the connection to the linearized stability analysis. The effect is then investigated in the context of isotropic emission from a supernova core. We show that an azimuthally isotropic flavor configuration is unstable under the differential equations of motion. We analyse the linear stability of propagation in the flavor state and the important consequences to the general prediction of collective flavor conversion. This symmetry-breaking instability is sensitive to the ordering of the neutrino masses.Wir untersuchen das Phänomen der spontanten Symmetriebrechung im Kontext kollektiver Neutrino-Flavour-Oszillationen. Insbesondere betrachten wir die spontane Brechung der Isotropie in einem homogenen Neutrinogas und die Brechung der azimuthalen Symmetrie im Kontext von Kernkollaps-Supernovae. Für das homogene Gas untersuchen wir ein einfaches eindimensionales Modell, um das Phänomen vorzuführen und die Verbindung zur lineariserten Stabilitätsanalyse herauszuarbeiten. Dann wird der Effekt im Kontext von isotroper Neutrinoausstrahlung aus einem Supernova-Kern angewandt. Wir zeigen, dass eine isotrope Flavour-Konfiguration unter den differ- entiellen Bewegungsgleichungen instabil ist. Wir analysieren die lineare Stabilität der Propagation im Flavour-Zustand und wichtige Konsequenzen für die allgemeine Vorhersage kollektiver Flavour- Konversion. Diese symmetriebrechende Instabilität wird von der Anordnung (“Hierarchie”) der Neutrinomassen beeinflusst.
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Sharan, Ujjawal. « Topology and chiral symmetry breaking in QCD ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302137.
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Gebauer, Astrid. « Chiral symmetry breaking transitions in holographic duals ». Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/206257/.
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Generalisations of the AdS/CFT Correspondence are used to study chiral symmetry breaking in dual gauge theories. We use the D3/D7 and D3/D5 systems to model both 3+1 and 2+1 dimensional, strongly coupled, gauge theories with quark fields. We show that chiral symmetry breaking is induced by either an imposed running coupling/dilaton profile or a background magnetic field. We explore the low energy effective theory of the pions of these models deriving simple integral equations for low energy parameters in the spirit of constituent quark model results. We also explore the phase structure of these models, with respect to temperature, chemical potential and applied electric field. The phase diagrams contain regions with broken and restored chiral symmetry separated by first order, second order and BKT transitions. There is an extra transition associated with the melting of the meson states into the background plasma. Finally we use the phenomenological dilaton profile to engineer holographic descriptions of theories with QCD-like phase diagrams.
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Smith, John Warren. « Dynamical chiral symmetry breaking in four-fermi theories ». Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30345.
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Dynamical symmetry breaking of discrete chiral symmetry in four-fermi models is studied. A variational method is used to determine the effective potential. This potential is then examined to determine the critical coupling for which a phase transistion between massless and massive states occurs. Two trial ground states are used in the variational calculation and the results are the same in each case. The first is the ground state of a free massive fermion and the other is a generalized Bogoliobov-Valatin transformation of a free massless fermion ground state. In each case dynamical symmetry breaking occurs, if the coupling is fine-tuned. The results are shown to be valid for physical dimensions 1+1, 2+1 and 3+1 and compared with those of other variational methods and the 1/N expansion.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Cundy, Nigel. « Instantons, topology, and chiral symmetry breaking in QCD ». Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275509.
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Wiedemann, Urs Achim. « Constraints and spontaneous symmetry breaking in quantum field theory ». Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336764.
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Pangon, Vincent. « An RG study of models with spontaneous symmetry breaking ». Strasbourg, 2009. http://www.theses.fr/2009STRA6116.
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Lundström, Jakob. « Spontaneous symmetry breaking for dipolar Bose-Einstein condensates in multiwell potentials ». Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-150816.
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In this work, dipolar Bose-Einstein condensates in multiwell potentialsplaced to form dierent geometrical structures are studied theoretically inorder to determine how the ground state population of the particles in thepotential wells changes depending on the relative strength of the particlesdipole moment. In the analytical limit (neglecting intersite tunneling), asymmetry-breaking change in the number of wells that are populated byparticles is observed for all studied systems for a certain value of the rela-tive strength of the particles dipole moment. The numerical calculationsfor nonzero intersite tunneling show a non-degenerate bifurcation whichis not seen in the analytical limit.
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Almiron, Núria. « Chiral symmetry breaking and pattern selection in chemical and biological systems ». Doctoral thesis, Universite Libre de Bruxelles, 1988. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213330.
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Ramos, Elena Garcia. « Investigations of chiral symmetry breaking and topological aspects of lattice QCD ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16890.
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Die spontane Brechung der chiralen Symmetrie ist ein faszinierendes Phenomän der QCD mit fundamentalen phänomenologischen Implikationen. Die Brechung der chiral Symmetrie ist beispielsweise verantwortlich für die niedrige Masse der Pionen, welche die effektiven Goldstone Boson der spontan gebrochene Symmetrie sind. Die spontane Brechung der chiral Symmetrie und die chirale Anomalie sind niedrig Energie-Phenomäne der QCD, weshalb nichtperturbative Methoden nötig sind um sie zu studieren. In der vorliegenden Arbeit verwenden wir die Gitterregularisierung der QCD, um das chirale Kondensat, den Ordnungsparameter der spontanen Brechung der chiralen Symmetrie zu bestimen. Dazu wendeten wir die Definition der in dieser Arbeit studierten Observablen über Dichteketten an, die eine theoretisch wohldefinierte Bahndlung der Observablen zulässt. Für die praktische Berechnung wurde die kürzlich entwickelte Methode der spektralen Projektoren angewandt. In dieser Weise berchnen wir den Kontinuumlimes des chiralen Kondensates, das im chiralen Limes gewonnen, sowohl für N_f=2 als auch für N_f=2+1+1 Flavour von so genannten twisted mass Fermionen. Des Weiteren untersuchen wir das chirale Verhalten der topologischen Suszeptibilität. Wir verwenden hier wieder die Methode der spektralen Projektoren, anstelle aufwendigerer Verfahren, die chirale Symmetrie erhalten, aber zu numerisch sehr aufwändigen Simulationen führen. Schließ lich kommentieren wir die sich aus den starken Autokorrelationen ergebenden Schwierigkeiten dieser Rechnung. Abschließ end stellen wir die Kontinuumlimes-Ergebnisse der topologischen Suszeptibilität in der rein gluonischen Theorie vor, die es uns erlauben, die Witten-Veneziano-Formel zu testen. Unseren Untersuchung zufolge ist diese Formel gut erfüllt. Diese Tatsache stützt die Gültigkeit der Formel, die die topologischen Fluktuationen der Eichfelder mit der unerwartet groß en Masse des eta'' Mesons in Verbindung setzt.The spontaneous breaking of chiral symmetry is a fascinating phenomenon of QCD whose mechanism is still not well understood and it has fundamental phenomenological implications. It is, for instance, responsible for the low mass of the pions which are effectively Goldstone bosons of the spontaneously broken symmetry. Since these phenomena belong to the low energy regime of QCD, non-perturbative techniques have to be applied in order to study them. In this work we use the twisted mass lattice QCD regularization to compute the chiral condensate, the order parameter of spontaneous chiral symmetry breaking. To this end we apply the recently introduced method of spectral projectors which allows us to perform calculations in large volumes due to its inherently low computational cost. This approach, moreover, enables a direct calculation of the chiral condensate based on a theoretically clean definition of the observable via density chains. We thus present a continuum limit determination of the chirally extrapolated condensate for N_f=2 and N_f=2+1+1 flavours of twisted mass fermions at maximal twist. In addition we study the chiral behavior of the topological susceptibility, a measure of the topological fluctuations of the gauge fields. We again apply the spectral projector method for this calculation. We comment on the difficulties which appear in the calculation of this observable due to the large autocorrelations involved. Finally we present the continuum limit result of the topological susceptibility in the pure gluonic theory which allows us to perform a test of the Witten-Veneziano relation. We found that this relation is well satisfied. Our results support the validity of the Witten-Veneziano formula which relates the topological fluctuations of the gauge fields with the unexpectedly large value of the eta''
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Toucas, Guillaume. « Mécanisme de brisure de symétrie chirale pour trois saveurs de quarks légers et extrapolation de résultats de chromodynamique quantique sur réseau ». Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00754994.
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Dans cette thèse, nous nous intéressons à certains aspects concernant les phénomènes hadroniques à basse énergie sous 1 GeV, en dessous de laquelle la symétrie chirale de la Chromodynamique Quantique (QCD) est spontanément brisée. En dessous de cette échelle d'énergie, le spectre de QCD se réduit à un octet de mésons légers pseudo-scalaires (π, K and η). Mais à cause du confinement, QCD sous 1 GeV devient hautement non perturbative - il n'est donc plus possible de décrire à basse énergie la dynamique de ces mésons en termes de gluons et de quarks (ici seuls les quarks légers u, d et s sont concernés). Deux alternatives principales à cet obstacle majeur existent néanmoins: la QCD sur réseau ainsi que les Théories Effectives des Champs. La QCD sur réseau consiste à calculer de manière numériques les diverses observables hadroniques, alors que les théories effectives permettent de nouveau une approche analytique (et perturbative) adaptée à une échelle d'énergie donnée. Dans le cas de QCD à basse énergie, c'est la Théorie Chirale des Perturbations (ChiPT) qui joue le rôle de théorie effective. Cette théorie peut être construite à partir de deux saveurs de quarks légers (u et s) ou trois (u,d, et s). Il est alors possible d'utiliser certains résultats de calculs sur réseau (ainsi que certains résultats expérimentaux) afin d'extraire des valeurs numériques pour les divers paramètres libres que contient la théorie chirale. Il fut néanmoins observé que le développement en séries chirales de quelques observables hadroniques sont numériquement "malades" dans le cadre de la théorie à trois saveurs. En effet, des travaux antérieurs montrent qu'il pourrait exister une possible compétition numérique entre l'Ordre Dominant (LO) et l'Ordre Sous-Dominant (NLO): en place de la hiérarchie usuelle LO>>NLO, l'équivalence LO~NLO prévalerait. La partie principale de la thèse consiste ainsi à la description et l'utilisation d'une version alternative de ChiPT, nommée Théorie Chirale des Perturbations Ressommée (ReChiPT ). Quelques observables hadroniques de basse energie sont calculées puis étudiées dans ce cadre "ressommé", puis nous procédons à l'ajustement de certaines données de QCD sur réseau obtenues par des simulations à 2+1 quarks dynamiques sur ces observables exprimées en ReChiPT: les constantes de désintégrations et les masses de l'octet (π, K, η), ainsi que les facteurs de forme Kl3. Nous testons ensuite la validité de notre assertion concernant la possible compétition numérique observée dans les séries chirales. Enfin, dans la dernière partie, nous discutons plusieurs aspects analytiques et numériques concernant certaines quantités topologiques liées de manière intrinsèque à la très complexe structure du vide de QCD, dans le cadre de ChiPT (ressommé), et nous confrontons de nouveau cette étude à des données réseau 2+1.
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Deutschländer, Sven [Verfasser]. « Melting and spontaneous symmetry breaking in two-dimensional colloidal systems / Sven Deutschländer ». Konstanz : Bibliothek der Universität Konstanz, 2015. http://d-nb.info/1098136438/34.
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Winterer, Felix Simon [Verfasser], et Thomas [Akademischer Betreuer] Weitz. « Spontaneous symmetry-breaking in trilayer graphene / Felix Simon Winterer ; Betreuer : Thomas Weitz ». München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2021. http://d-nb.info/1234912031/34.
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Carignano, Stefano Verfasser], Michael [Akademischer Betreuer] Buballa et Jochen [Akademischer Betreuer] [Wambach. « Inhomogeneous chiral symmetry breaking phases / Stefano Carignano. Betreuer : Michael Buballa ; Jochen Wambach ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2012. http://d-nb.info/1106256719/34.
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Doi, Takahiro. « Lattice QCD study for the relation between confinement and chiral symmetry breaking ». 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225399.
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Carignano, Stefano [Verfasser], Michael Akademischer Betreuer] Buballa et Jochen [Akademischer Betreuer] [Wambach. « Inhomogeneous chiral symmetry breaking phases / Stefano Carignano. Betreuer : Michael Buballa ; Jochen Wambach ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2012. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-31493.
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Sousa, Seixas David de [Verfasser], et Georg [Akademischer Betreuer] Raffelt. « Spontaneous symmetry breaking in collective neutrino oscillations / David de Sousa Seixas. Betreuer : Georg Raffelt ». München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1063874955/34.
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Wilming, Henrik [Verfasser]. « A Quantum of Thermodynamics : From ground state cooling to spontaneous symmetry breaking / Henrik Wilming ». Berlin : Freie Universität Berlin, 2018. http://d-nb.info/117663643X/34.
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Cárcamo, Hernández Antonio Enrique. « Composite Vectors and Scalars in Theories of Electroweak Symmetry Breaking ». Doctoral thesis, Scuola Normale Superiore, 2011. http://hdl.handle.net/11384/85833.
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In the context of a strongly coupled Electroweak Symmetry Breaking, composite triplet of heavy
vectors belonging to the SU(2)L+R adjoint representation and a composite scalar singlet under
SU(2)L+R may arise from a new strong interaction invariant under the global SU(2)L x S(2)R symmetry, which is spontaneously broken down to SU(2)L+R. This thesis consists of two parts.
The first part is devoted to the study of the heavy composite vector pair production at the LHC
via Vector Boson Fusion and Drell-Yan annihilation under the assumption that the interactions
among these heavy vector states and with the Standard Model gauge bosons are described by
a SU(2)L x SU(2)R=SU(2)L+R Effective Chiral Lagrangian. The expected rates of multi-lepton
events from the decay of the composite vectors are also given. The second part studies the
associated production at the LHC of a composite vector with a composite scalar by Vector Boson
Fusion and Drell-Yan annihilation in the framework of a SU(2)L x SU(2)R=SU(2)L+R Effective
Chiral Lagrangian with massive spin one fields and one singlet light scalar. The expected rates of
same sign di-lepton and tri-lepton events from the decay of the composite vector and composite
scalar final state are computed. The connection of the Effective Chiral Lagrangians with suitable
gauge models is elucidated.
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Lebedev, Oleg. « Spontaneous CP-Violation in Two Higgs Doublet Supersymmetric Models ». Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30640.
Texte intégralRésumé :
An alternative approach to the problem of CP-violation
is presented. It is based on the possibility of
spontaneous CP-breakdown in models with two Higgs doublets.
General features of the phenomenon such as stability of the
vacuum and the existence of a light axion are discussed.
We investigate the feasibility of spontaneously broken
CP in the minimal supersymmetric models - the MSSM and
NMSSM. The latter is shown to be experimentally viable.
The phenomenological implications of the model such as
CP-violating effects in the kaon systems and a nonzero
neutron electric dipole moment are studied.Ph. D.
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Capdevilla, Roldan Rodolfo Maia [UNESP]. « Dynamical chiral symmetry breaking : the fermionic gap equation with dynamical gluon mass and confinement ». Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/92026.
Texte intégralRésumé :
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capdevillaroldan_rm_me_ift.pdf: 1695600 bytes, checksum: 56f8cc2724bbe924e0b430ebe1a3b24e (MD5)Alguns aspectos da quebra de simetria quiral para quarks na representação fundamental são discutidos no contexto das equações de Schwinger-Dyson. Estudamos a equação de gap fermionica incluindo o efeito de uma massa dinêmica para os gluons. Ao estudar esta equação de gap verificamos que a intenção não é forte o suficiente para gerar uma massa dinâmica dos quarks compatível com os dados experimentais. Também discutimos como a introdução de um propagador confinante pode mudar este cenário, exatamente como foi proposto por Cornwall [1] recentemente, desta forma estudamos uma equação de gap completa, composta pela troca de um gluon massivo e por um termo confinante; M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). Encontramos soluções assintótica desta equação de gap nos casos de constante de acoplamento constante e corredora. Este último caso corresponde a um aprimoramento do cálculo com constante de acoplamento constante feito por Doff, Machado e Natale [2]
Some aspects of chiral symmetry breaking for quarks in the fundamental representation are discussed in the framework of the Schwinger-Dyson equations. We study the fermionic gap equation including effects of dynamical gluon mass. Studying the bifurcation equation of this gap equation we verify that the interaction is not strong enough to generate a satisfactory dynamical quark mass. We also discuss how the introduction of a confining propagator may change this scenario as recently pointed out by Cornwall [1], so we study a complete gap equation composed by the one-dressed-gluon exchange term and a confining term: M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). We find asymptotic solutions for this gap equation in the cases of constant coupling and running coupling constant. This last case is an improvement of the constant coupling calculation of Doff, Machado and Natale [2]
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Capdevilla, Roldan Rodolfo Maia. « Dynamical chiral symmetry breaking : the fermionic gap equation with dynamical gluon mass and confinement / ». São Paulo, 2013. http://hdl.handle.net/11449/92026.
Texte intégralRésumé :
Orientador: Adriano Antonio NataleBanca: Adriano Doff Sotta Gomes
Banca: Alex Gomes Dias
Resumo: Alguns aspectos da quebra de simetria quiral para quarks na representação fundamental são discutidos no contexto das equações de Schwinger-Dyson. Estudamos a equação de gap fermionica incluindo o efeito de uma massa dinêmica para os gluons. Ao estudar esta equação de gap verificamos que a intenção não é forte o suficiente para gerar uma massa dinâmica dos quarks compatível com os dados experimentais. Também discutimos como a introdução de um propagador confinante pode mudar este cenário, exatamente como foi proposto por Cornwall [1] recentemente, desta forma estudamos uma equação de gap "completa", composta pela troca de um gluon massivo e por um termo confinante; M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). Encontramos soluções assintótica desta equação de gap nos casos de constante de acoplamento "constante" e "corredora". Este último caso corresponde a um aprimoramento do cálculo com constante de acoplamento "constante" feito por Doff, Machado e Natale [2]
Abstract: Some aspects of chiral symmetry breaking for quarks in the fundamental representation are discussed in the framework of the Schwinger-Dyson equations. We study the fermionic gap equation including effects of dynamical gluon mass. Studying the bifurcation equation of this gap equation we verify that the interaction is not strong enough to generate a satisfactory dynamical quark mass. We also discuss how the introduction of a confining propagator may change this scenario as recently pointed out by Cornwall [1], so we study a "complete" gap equation composed by the one-dressed-gluon exchange term and a confining term: M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). We find asymptotic solutions for this gap equation in the cases of "constant coupling" and "running coupling constant". This last case is an improvement of the constant coupling calculation of Doff, Machado and Natale [2]
Mestre
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Kokulu, Ahmet. « Eta-eta Prime Mixing In Chiral Perturbation Theory ». Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609808/index.pdf.
Texte intégralRésumé :
Quantum Chromodynamics (QCD) is believed to be the theory of strong
interactions. At high energies, it has been successfully applied to explain
the interactions in accelerators. At these energies, the method used to do
the calculations is perturbation theory. But at low energies, since the
strong coupling constant becomes large, perturbation theory is no longer
applicable. Hence, one needs non-perturbative approaches. Some of these
approaches are based on the fundamental QCD Lagrangian, such as the QCD sum
rules or lattice calculations. Some others use an effective theory approach
to relate experimental observables one to the other. Chiral Perturbation
Theory (ChPT) is one of these approaches. In this thesis, we make a review of chiral
perturbation theory and its applications to study the mixing phenomenon
between the neutral pseudoscalar mesons eta and eta-prime.
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Rispler, Manuel Verfasser], Norbert [Akademischer Betreuer] Schuch et Barbara [Akademischer Betreuer] [Terhal. « Spontaneous symmetry breaking in projected entangled pair state models / Manuel Rispler ; Norbert Schuch, Barbara Maria Terhal ». Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162450487/34.
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Rispler, Manuel [Verfasser], Norbert Akademischer Betreuer] Schuch et Barbara [Akademischer Betreuer] [Terhal. « Spontaneous symmetry breaking in projected entangled pair state models / Manuel Rispler ; Norbert Schuch, Barbara Maria Terhal ». Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162450487/34.
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Nowakowski, Daniel Verfasser], Michael [Akademischer Betreuer] Buballa et Jochen [Akademischer Betreuer] [Wambach. « Inhomogeneous chiral symmetry breaking in isospin-asymmetric strong-interaction matter / Daniel Nowakowski ; Michael Buballa, Jochen Wambach ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1131254228/34.
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Nowakowski, Daniel [Verfasser], Michael Akademischer Betreuer] Buballa et Jochen [Akademischer Betreuer] [Wambach. « Inhomogeneous chiral symmetry breaking in isospin-asymmetric strong-interaction matter / Daniel Nowakowski ; Michael Buballa, Jochen Wambach ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-61570.
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Masiteng, Paulus Lukisi. « Gamma spectroscopy and lifetime measurements in the doubly-odd 194tl nucleus, revealing possible chiral symmetry breaking ». University of the Western Cape, 2013. http://hdl.handle.net/11394/3991.
Texte intégralRésumé :
Philosophiae Doctor - PhDIn the first experiment high spin states in 194Tl, excited through the 181Ta (18O, 5n) heavyion fusion evaporation reaction were studied using the AFRODITE array at iThemba LABS. The γ-γ coincidences, RAD ratios and linear polarization measurements were carried out and the previously known level scheme of 194Tl was significantly extended. A total of five rotational bands four of which are new were observed. A pair of rotational bands associated with the πh9/2 ⊗ νi−1 13/2 configuration at lower spins and with the πh9/2 ⊗ νi−3 13/2 configuration at higher spins was found and interpreted as the first possible chiral bands followed above the band crossing. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. In the second experiment lifetimes in 194Tl were measured using the DSAM technique with the excited states in this nucleus populated through the 181Ta (18O, 5n) reaction. A total of 25 lifetimes and 30 reduced transition probabilities of magnetic dipole B(M1) and electric quadrupole B(E2) have been evaluated. Furthermore B(M1) and B(E2) reduced transition probabilities in Bands 1 and 4, which have been regarded as chiral candidates, were found to be close to each other and reveals strong splitting along spin values. This further supports the proposed chiral nature of these two bands.
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Usai, Alessandro. « Spontaneous CP violation in the next-to-minimal supersymmetric standard model ». Thesis, University of Glasgow, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323421.
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Wilhelm, Franz. « Construction of the Higgs Mechanism and the Lee-Quigg-Thacker-bound ». Thesis, Uppsala universitet, Högenergifysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388550.
Texte intégralRésumé :
In this paper the higgs mechanism for the standard model is constructed in steps. First by considering spontaneous breaking of discrete and continuous global gauge invariance. Then spontaneous breaking of local gauge invariance. These results are then used to construct the electroweak part of the standard model through application of the higgs mechanism. Finally, the LQT-upper bound of 1 TeV for the higgs mass is calculated through unitarity constraints.I denna artikel konstrueras higgsmekanismen i standardmodellen stegvis. Först genom att beakta spontant symmetribrott av diskreta samt kontinuerliga globala gaugeinvarianser. Därefter spontant symmetribrott av lokala gaugeinvarianser. Dessa resultat används sedan för att konstruera den elektrosvaga delen av standardmodellen genom tillämpning av higgsmekanismen. Slutligen beräknas en övre gräns för higgsmassan, den så kallade LQT-gränsen, via unitaritetsbegränsingar.
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Messina, Emanuele. « Non perturbative renormalization of firmion theories ». Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/936.
Texte intégralRésumé :
The present work is devoted to the study of the non-perturbative renormalization of quantum
field theories (QFT) of self-interacting fermions,
which is investigated with the help of a fermion Wilsonian RG method.
By starting with the appropriate scale dependent action S_k for fermion models and performing a non-trivial extension of previous techniques, a new renormalization group (RG) equation for a generalized N flavors Gross-Neveu model in 2 ¿ d ¿ 4 dimensions is established.
The renormalizability of such a model is related to the
existence of a non-Gaussian fixed point of the RG equations, which
turns out also to be related to the critical point of the
chiral symmetry breaking.
Within the Wilson RG approach to critical phenomena, the
critical exponents of the Gross-Neveu model are computed by considering the behaviour of the running mass m(k) and Fermi constant G(k)
around such a non-Gaussian fixed point (with divergent correlation length).
By means our approach, this model can be
studied even far from the applicability domain of other traditional analytical tools (as epsilon or 1/N expansion) relying on the bosonization
of the model.
The RG equations for the running mass m(k) and Fermi constant G(k)
are numerically studied in
the whole (G, m) plane. From this analysis, in turns out that the physics of the chiral
phase transition can be described well in terms of a cross-over phenomenon triggered by
the presence of an infinitesimal bare mass.
The impact of higher powers operators (¿¿)^4 in the Wilsonian potential is also considered.
In the large N limit,
the failure of the hyperscaling and the presence of
a logarithmic behaviour at d=4 dimensions with the scale of the quartic operator (¿¿)^4 are thus recovered in our RG fermion language.
By considering the impact of odd interaction terms in the potential, the marginality
of the cubic operator in d = 3 dimensions is also recovered. The anomalous dimension of this
operator is computed and found to be in agreement with results given in the literature at
the next to leading order in the 1/N expansion.
Finally the Wilsonian RG equation is extended to theories which involve both fermions
and bosons. For N=1 and d=4 this equation coincides with that found in
literature. A non-trivial FP which should describe the chiral transition for
d<4 is then found.
If, however, a four Fermi interaction term is added to the Yukawa theory,
an intriguing and unexpected result is found. Namely, the non-perturbative
scaling of the running Fermi constant G(k) triggers the appearence of a
non-Gaussian fixed point which heals the triviality of the Yukawa coupling
in d=4 dimensions.
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Garcia, Ramos Elena [Verfasser], Karl [Akademischer Betreuer] Jansen, Michael [Akademischer Betreuer] Müller-Preußker et Giancarlo [Akademischer Betreuer] Rossi. « Investigations of chiral symmetry breaking and topological aspects of lattice QCD / Elena Garcia Ramos. Gutachter : Karl Jansen ; Michael Müller-Preußker ; Giancarlo Rossi ». Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://d-nb.info/1047399180/34.
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Garcia-Ramos, Elena [Verfasser], Karl [Akademischer Betreuer] Jansen, Michael [Akademischer Betreuer] Müller-Preußker et Giancarlo [Akademischer Betreuer] Rossi. « Investigations of chiral symmetry breaking and topological aspects of lattice QCD / Elena Garcia Ramos. Gutachter : Karl Jansen ; Michael Müller-Preußker ; Giancarlo Rossi ». Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://nbn-resolving.de/urn:nbn:de:kobv:11-100215415.
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Böhmer, Christian [Verfasser], et Michael [Akademischer Betreuer] Thies. « Explicit chiral symmetry breaking in Gross-Neveu type models = Explizite chirale Symmetriebrechung in Modelltheorien vom Gross-Neveu Typ / Christian Böhmer. Betreuer : Michael Thies ». Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2011. http://d-nb.info/1015475000/34.
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Uwaha, Makio. « Simple Models for Chirality Conversion of Crystals and Molecules by Grinding ». The Physical Society of Japan, 2008. http://hdl.handle.net/2237/13865.
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Hössjer, Emil. « Generalized Abelian Gauge Theory & ; Generalized Global Symmetry ». Thesis, Uppsala universitet, Teoretisk fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-434474.
Texte intégralRésumé :
We study Cheeger-Simons differential characters in order to define higher form U(1) gauge fields and their Wilson lines. We then go on to define generalized global symmetries. This is a topological formulation of symmetries which has interesting consequences when the charged operators extend through space. Our main source of such charged operators are the generalized Wilson lines. A higher form Noether theorem and a Ward identity are given for transformations of Wilson lines. As examples of quantum field theories with generalized symmetries we cover Sigma models, Maxwell theory and BF-theory. These are examples of Z, U(1) and Zn symmetries respectively. Finally we discuss spontaneous symmetry breaking for higher dimensional symmetries and a Goldstone theorem is provided. These massless Goldstone bosons are shown to have internal structure corresponding to non-zero spin. The photon is identified as the spin one Goldstone boson in QED. Our review of generalized symmetries is more formal than the ones in other papers. This makes various points explicit and leads to general selection rules. Many results of previous papers are reproduced in detail.
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Uzan, Pierre. « Conscience et physique quantique ». Thesis, Paris 4, 2010. http://www.theses.fr/2010PA040153.
Texte intégralRésumé :
Ce travail a pour objet d'évaluer l'apport de la physique quantique à la compréhension du phénomène de la conscience. Les modèles « classiques » de la conscience proposés actuellement laissent en suspens deux questions importantes: (a) l'explication de la synchronisation de régions éloignées du cerveau qui semble nécessaire à la construction de percepts conscients ; (b) la question du fossé explicatif qui existe entre l'expérience subjective, relevant de ce que le sujet est capable de ressentir de façon privée, et la description de ses corrélats neurophysiologiques dans le langage de la science, à la troisième personne. Les approches quantiques de la conscience sont systématiquement exposées et critiquées. Le « modèle dissipatif du cerveau »proposé par Vitiello et Freeman semble corroborer les données expérimentales et pourrait ainsi contribuer à résoudre cette dernière question (a). Ce modèle utilise une propriété fondamentale de la théorie quantique des champs selon laquelle la brisure spontanée de symétrie au sein d'un système physique donne lieu à l'émergence d'une dynamique collective pour ce système. Les modèles, relavant de la conception du monismeneutre, qui ont développés par Bohm et Hiley, et, plus récemment, par Atmanspacher et Primas, utilisent la théorie quantique pour son pouvoir expressif (concepts de complémentarité et d'intrication) et non comme une théorie de la seule matière pour bâtir une représentation unificatrice du phénomène de la conscience. Ils permettent de dissoudre la question (b) du fossé explicatif. Nous proposons enfin de prolonger et d'appliquer,plus généralement, ce mode de représentation au domaine psychosomatiqueThis work aims to assess the contribution of quantum physics to the understanding of the phenomenon ofconsciousness. The "classical" models of consciousness cannat deal with two important questions: (a) thesynchronisation of distant parts of the brain which seems necessary to the construction of conscious percepts;(b) the question of the explanatory gap that exists between subjective experience, which is a private feeling, andthe description of its neurophysiological correlates in the language of science, at the third persan. The quantumalternatives of current models of consciousness are systematically exposed. Vitiello's and Freeman's "dissipativemadel of the brain" seem to corroborate experimental data and could thus contribute to solve question (a). Thismadel appeals to a fundamental property of quantum field theory according to which a spontaneous symmetrybreaking in a physical system (as it happens, the breaking of the rotational symmetry of dipolar molecules of thebrain) gives rise to a collective dynamics for this system. The models, relevant to the neutra! monism conception,that have been developed by Bohm and Hiley and, more recently, by Atmanspacher and by Primas use quantumtheory for its expressive power (concepts of complementarity and entanglement) to build a unifyingrepresentation of the phenomenon of consciousness. They lead to the dissolution of the question (b) of theexplanatory gap. ln the end, we suggest to extend this mode of representation and to apply it, more generally, tothe psychosomatic domain
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Jurkovich, Heitor do Amaral 1990. « Uma introdução à teoria quântica de campos = quebra espontânea de simetria ». [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277000.
Texte intégralRésumé :
Orientador: Marcelo Moraes GuzzoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Nessa dissertação foi estudada a quebra espontânea de simetria desde suas bases mais fundamentais. A quebra espontânea de simetria e o único mecanismo conhecido capaz de gerar massas a uma teoria, preservando as simetrias e sendo renormalizável. Tal processo ocorre quando se define um setor escalar para uma teoria com uma certa simetria e se quebra os geradores dessa simetria, criando bosons de Goldstone no caso de simetrias globais e campos de gauge massivos, no caso de simetrias locais. Nessa dissertação começamos o estudo de quebra espontânea de simetria com um estudo de Teoria de Grupos, que e fundamental para o entendimento da mesma seguido por um estudo em simetrias nas lagrangianas, ou seja, como gerar uma lagrangiana invariante por um dado grupo, local ou global; depois estudamos o Teorema de Goldstone e por m aplicamos a quebra espontânea de simetria para diversos modelos, entre eles o campo escalar, campo escalar complexo com simetria global, campo escalar complexo com simetria local, modelo padrão. Depois fazemos um estudo em uma das extensões do modelo padrão, o modelo SU(5) e aplicamos a quebra espontânea de simetria em tal modelo. No m mostramos como a abordagem de minimização de um potencial clássico e valida, pois contribuições quântica são análogas a uma energia de ponto zero ao potencial efetivo
Abstract: A detailed study of the spontaneous symmetry breaking since its fundamental basis is done. The spontaneous symmetry breaking is the only know mechanism capable of generating masses to a theory still preserving its symmetry and being renormalizable. Such process occurs when one defines a scalar sector to a certain theory with a symmetry and then break the generators of this symmetry, creating Goldstone bosons in the case of global symmetries and massive gauge fields in the case of local symmetries. We start this dissertation studying Group Theory, which is fundamental to the understanding of spontaneous symmetry breaking. Then we study local and global symmetries of the lagrangian, Goldstone Theorem, then spontaneous symmetry breaking to several models, including the scalar theory, complex scalar theory with global and local symmetries and the standard model. Then we make a study in one of the standard model extensions, the SU(5) model and we applied spontaneous symmetry breaking to this model. In the end we show that the approach of minimizing que classical potential is valid because quantum contributions are analogous to a zero point energy to the effective potential
Mestrado
Física
Mestre em Física
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Junior, Fernando Martins Antoneli. « Grupos finitos e quebra de simetria no código genético ». Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/45/45132/tde-07102009-143515/.
Texte intégralRésumé :
Neste trabalho resolvemos o problema da classicação dos possíveis esquemas de quebra de simetria que reproduzem as degenerescências do código genético na categoria dos grupos finitos simples, contribuindo assim para a busca de modelos algébricos para a evolução do código genético, iniciada por Hornos & Hornos.In this work we solve the problem of classifying the possible symmetry breaking schemes based on simple finite groups that reproduce the degeneracies of the genetic code, thus contributing to the search for algebraic models that describe the evolution of the genetic code, initiated by Hornos & Hornos.
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Pakalidou, Nikoletta. « Self-assembly of two-dimensional convex and nonconvex colloidal platelets ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/selfassembly-of-twodimensional-convex-and-nonconvex-colloidal-platelets(072e9fad-3e34-4803-b3df-6aed3ce756c7).html.
Texte intégralRésumé :
One of the most promising routes to create advanced materials is self-assembly. Self-assembly refers to the self-organisation of building blocks to form ordered structures. As the properties of the self-assembled materials will inherit the properties of the basic building blocks, it is then possible to engineer the properties of the materials by tailoring the properties of the building blocks. In order to create mesoscale materials, the self-assembly of molecular building blocks of different sizes and interactions is important. Mesoscopic materials can be obtained by using larger building blocks such as nano and colloidal particles. Colloidal particles are particularly attractive as building blocks because it is possible to design interparticle interactions by controlling both the chemistry of the particles' surface and the properties of the solvent in which the particles are immersed. The self-assembly of spherical colloidal particles has been widely reported in the literature. However, advances in experimental techniques to produce particles with different shapes and sizes have opened new opportunities to create more complex structures that cannot be formed using spherical particles. Indeed, the particles' shape and effective interactions between them dictate the spatial arrangement and micro-structure of the system, which can be engineered to produce functional materials for a wide range of applications. The driving forces determining the self-assembly of colloidal particles can be modified by the use of external influences such as geometrical confinement and electromagnetic forces. Geometrical confinement, for example, has been used to design quasi two-dimensional materials such as multi-layered structures of spheres, dimers, rods, spherical caps, and monolayers of platelets with various geometries and symmetries. In this dissertation, we present three computer simulations studies using Monte Carlo and Molecular Dynamics simulations determining the self-assembly of monolayer colloidal platelets with different shapes confined in two dimensions. These particles have been selected due to recent experiments in colloidal particles with similar shapes. All the particles' models are represented by planar polygons, and three different effects affecting their self-assembly have been analysed: (a) the curvature of the particles' vertices; (b) the curvature of the particles' edges; and finally (c) the addition of functional groups on the particles' surface. These studies aim to demonstrate that the subtle changes on the particle's shape can be used to engineer complex patterns for the fabrication of advanced materials. Monte Carlo simulations are performed to study the self-assembly of colloidal platelets with rounded corners with 4, 5, and 6-fold symmetries. Square platelets provide a rich phase behaviour that ranges between disorder-order and order-order phase transitions. Suprisingly, the disk-like shape of pentagons and hexagons prevents the total crystallisation of these systems, even at a high pressure state. A hysteresis gap is observed by the analysis of compression and expansion runs for the case of square platelets and the thermodynamic method known as direct coexistence method is used to be accurately determined the point of the order-order transition. Further, unexpected results are obtained by performing Molecular Dynamics simulations in systems with platelets with 3, 4, 5, and 6-fold symmetries when all the sides of each polygon are curved. Macroscopic chiral symmetry breaking is observed for platelets with 4 and 6-fold symmetries, and for the first time a rule is promoted to explain when these chiral structures can be formed driven only by packing effects. This unique rule is verified also for platelets with the same curved sides as previously when functional chains tethered to either vertices or sides. Indeed, square platelets with curved sides confined in two dimensions can form chiral structures at medium densities when flexible chains tethered to either vertices or sides. Triangular platelets with curved sides can form chiral structures only when the chains are tethered to the corners, since the chains experience an one-hand rotation to sterically protect one side. When the chains are symmetrically tethered to the sides, local chiral symmetry breaking is observed as both left-hand and right-hand sides on each vertex are sterically protected allowing the same probability for rotation either in clockwise or anticlockwise direction.
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Silva, Paulo José Ferreira Porfírio da. « Modelo de dois dubletos de higgs ». Universidade Federal da Paraíba, 2013. http://tede.biblioteca.ufpb.br:8080/handle/tede/5756.
Texte intégralRésumé :
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Previous issue date: 2013-03-07Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this dissertation we did a complete review of the StandardModel(SM), emphasizing the weak interactions, this in order to treat an extension of theMP with addition of a doublet of scalar theory, known in the literature asModel with Two Higgs doublets (2HDM). We will treat this model from the point of view of both aspects: when two doublets develop the expected value of the vacuum(vev) and when only one develops doublets vev, utilize the potential of 2HDM does not violate CP. These two models are particularly important because they are quite simple and can solve some problems that are open in Physics, one of the most important is the dark matter (DM). Furthermore, we will use the formalism of oblique parameters, radiative corrections involving first order, to parameterize the effects of New Physics (NP). We will present the phenomenology to obtain 2HDMI and regions that are in agreement with the experimental data.
Nesta dissertação fizemos uma revisão completa doModelo Padrão (MP), dando ênfase as interações fracas, isto com o intuito de tratarmos de uma extensão do MP com adição de um dubleto de escalar a teoria, conhecida na literatura como Modelo com Dois Dubletos de Higgs(2HDM)1. Iremos tratar deste modelo sob o ponto de vista de dois aspectos: quando os dois dubletos desenvolvem valor esperado do vácuo(vev) e quando apenas um dos dubletos desenvolve vev, utilizamos o potencial do 2HDM que não viola CP. Particularmente, esses dois modelos são importantes porque eles são bastante simples e podemresolver alguns problemas que estão emaberto na Física, um dosmais importantes é amatéria escura(ME). Além disso, iremos utilizar o formalismo de parâmetros oblíquos, que envolve correções radiativas de primeira ordem, para parametrizar os efeitos da Nova Física(NF). Apresentaremos a fenomenologia para o 2HDMI e obteremos as regiões que estão de acordo com os dados experimentais.
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Bansal, Sukruti. « Goldstone Fields with Spins Higher than 1/2 ». Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3421854.
Texte intégralRésumé :
We study three-dimensional non-linear models of vector and vector-spinor Goldstone fields associated with the spontaneous breaking of certain higher-spin counterparts of supersymmetry. The Lagrangians in these models are of a Volkov-Akulov type. Goldstone fields in these models transform non-linearly under the spontaneously broken rigid symmetries. We find that the leading term in the action of the vector Goldstone model is the Abelian Chern-Simons action whose gauge symmetry is broken by a quartic term. As a result, the model has a propagating degree of freedom which, in a decoupling limit, is a quartic Galileon scalar field. The vector-spinor goldstino model turns out to be a non-linear generalization of the three-dimensional Rarita-Schwinger action. In contrast to the vector Goldstone case, this non-linear model retains the gauge symmetry of the free Rarita-Schwinger action and eventually reduces to the latter by a non-linear field redefinition. We thus find that the free Rarita-Schwinger action is invariant under a hidden rigid supersymmetry generated by fermionic vector-spinor operators and acting non-linearly on the Rarita-Schwinger goldstino.
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Maelger, Jan. « Perturbative perspectives on the Phase diagram of Quantum ChromoDynamics ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX050/document.
Texte intégralRésumé :
L'étude du diagramme des phases de la Chromodynamique Quantique (QCD) et des transitons associées (déconfinement et restoration de la symétrie chirale) représentent des défis majeurs de la Physique moderne et nombreuses sont les approches théoriques qui visent à en sonder les multiples facettes. Du fait de l'intensité de l'interaction forte dans les régimes d’énergie pertinents pour les transitions susmentionnées, ces approches sont en général de nature non-perturbative, la théorie des perturbations étant réputée inapplicable à ces échelles. Il est, cependant, bien établi que le point de départ de la théorie usuelle des perturbations, basée sur la procédure de fixation de jauge de Faddeev-Popov, est ambigu à ces échelles (ambiguïté de Gribov). Dans ce contexte, une approche perturbative modifiée, basée sur le Lagrangien de Curci et Ferrari, a été proposée, via l’ajout phénoménologique d'un terme de masse effectif pour le gluon en jauge de Landau. Cette approche a été testée avec succès, notamment dans sa capacité à reproduire les fonctions de corrélation de la théorie Yang-Mills (et QCD dans la limite de quarks lourds) et la thermodynamique à temperature et potentiel chimique non nuls.Dans cette thèse, nous avons testé la robustesse de ces résultats en évaluant la structure de phase de la QCD avec quarks lourds au deuxième ordre de la théorie des perturbations dans le modèle de Curci-Ferrari et en comparant nos résultats à ceux d'approches nonperturbatives. Nos résultats indiquent que, dans ce régime de quarks lourds, le diagramme de phases est contrôlée perturbativement. Nous avons égalementétendu notre étude au cas de la QCD avec quarks légers en utilisant un schéma de resommation qui exploite la présence de petits paramètres dans le régime infrarouge de la QCD. Dans le secteur des quarks, cette démarche donne lieu à la resommation des fameux diagrammes dits "arc-en-ciel”. Ici, nous généralisons ce formalisme à temperature et densité non nulles et en presence d'un champ de fond gluonique. Nous réalisons une toute première étude qualitative des prédictions du modèle CF concernant l’existence possible d’un point critique dans le diagramme de phases de QCD sur la base d’une version simplifiée des équations générales ainsi obtenuesUnravelling the structure of the QCD phase diagram and its many aspects such as (de)confinementand chiral symmetry breaking, is one of the big challenges of modern theoretical physics, and manyapproaches have been devised to this aim. Since perturbation theory is believed to cease feasibilityat low energy scales, these approaches treat the relevant order parameters, the quark condensate andthe Polyakov loop, non-perturbatively. However, it is also well-established that the starting point forperturbation theory, the Fadeev-Popov gauge-fixing procedure, is inherently ill-defined in the infrareddue to the presence of Gribov ambiguities. In this context, a modified perturbative approach based onthe Curci-Ferrari Lagrangian has been introduced, where a phenomenologically motivated effective gluonmass term is added to the Landau gauge-fixed action. Prior to the beginning of the thesis, this approach hasproven extremely fruitful in its descriptions of (unquenched) Yang-Mills correlation functions and thermodynamics at (non)zero temperature and density.Throughout the thesis we extend this analysis to the entire phase structure of QCD and QCD-liketheories and test the validity of the model in various regimes of interest. For instance, to further aprevious one-loop study in the regime of heavy quark masses, we have computed the two-loop quarksunset diagram in the presence of a non-trivial gluon background in a finite temperature and densitysetting. We come to the conclusion that the physics underlying center symmetry is well-described by our perturbative model with a seemingly robust weak-coupling expansion scheme. Furthermore, we study the regime of light quarks by means of a recently proposed resummation scheme which exploits the presence of actual small parameters in the Curci-Ferrari description of infrared QCD. In the quark sector, this leads to the renown rainbow equations. We extend this first-principle setup to nonzero temperature, chemical potential, and gluon background. We perform a first qualitative analysis of the prediction of the model concerning the possible existence of a critical endpoint in the QCD phase diagram by using a simplified version of these general equations
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Fischer, André. « Advanced Cluster Methods for Correlated-Electron Systems ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-191382.
Texte intégralRésumé :
In this thesis, quantum cluster methods are used to calculate electronic properties of correlated-electron systems. A special focus lies in the determination of the ground state properties of a 3/4 filled triangular lattice within the one-band Hubbard model. At this filling, the electronic density of states exhibits a so-called van Hove singularity and the Fermi surface becomes perfectly nested, causing an instability towards a variety of spin-density-wave (SDW) and superconducting states. While chiral d+id-wave superconductivity has been proposed as the ground state in the weak coupling limit, the situation towards strong interactions is unclear.
Additionally, quantum cluster methods are used here to investigate the interplay of Coulomb interactions and symmetry-breaking mechanisms within the nematic phase of iron-pnictide superconductors. The transition from a tetragonal to an orthorhombic phase is accompanied by a significant change in electronic properties, while long-range magnetic order is not established yet. The driving force of this transition may not only be phonons but also magnetic or orbital fluctuations. The signatures of these scenarios are studied with quantum cluster methods to identify the most important effects.
Here, cluster perturbation theory (CPT) and its variational extention, the variational cluster approach (VCA) are used to treat the respective systems on a level beyond mean-field theory. Short-range correlations are incorporated numerically exactly by exact diagonalization (ED). In the VCA, long-range interactions are included by variational optimization of a fictitious symmetry-breaking field based on a self-energy functional approach. Due to limitations of ED, cluster sizes are limited to a small number of degrees of freedom.
For the 3/4 filled triangular lattice, the VCA is performed for different cluster symmetries. A strong symmetry dependence and finite-size effects make a comparison of the results from different clusters difficult. The ground state in the weak-coupling limit is superconducting with chiral d+id-wave symmetry, in accordance to previous renormalization group approaches. In the regime of strong interactions SDW states are preferred over superconductivity and a collinaer SDW state with nonuniform spin moments on a quadrupled unit cell has the lowest grand potential. At strong coupling, inclusion of short-range quantum fluctuations turns out to favor this collinear state over the chiral phase predicted by mean-field theory. At intermediate interactions, no robust conclusion can be drawn from the results.
Symmetry-breaking mechanisms within the nematic phase of the iron-pnictides are studied using a three-band model for the iron planes on a 4-site cluster. CPT allows a local breaking of the symmetry within the cluster without imposing long-range magnetic order. This is a crucial step beyond mean-field approaches to the magnetically ordered state, where such a nematic phase cannot easily be investigated. Three mechanisms are included to break the fourfold lattice symmetry down to a twofold symmetry. The effects of anisotropic magnetic couplings are compared to an orbital ordering field and anisotropic hoppings. All three mechanisms lead to similar features in the spectral density. Since the anisotropy of the hopping parameters has to be very large to obtain similar results as observed in ARPES, a phonon-driven transition is unlikely.
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Gaydutschenko, Larissa 1987. « Matrizes de massa e violação CP ». [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278509.
Texte intégralRésumé :
Orientador: Orlando Luis Goulart PeresDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: O fenômeno de oscilação de neutrinos, já experimentalmente observado, só pode ser explicado se a massa dos neutrinos for diferente de zero. No entanto, até pouco tempo atrás, acreditava-se que neutrinos não tivessem massa. O Modelo Padrão das partículas elementares ainda não é capaz de descrever a natureza massiva dos neutrinos, de forma que as matrizes de mistura para léptons (entre autoestados de gauge e autoestados de massa), análogas às matrizes de mistura de quarks, ainda não podem ser encontradas. Através de uma pequena extensão do Modelo Padrão, é possível descrever uma física que leva em conta essas massas e que, portanto, nos fornece essas matrizes de mistura. Essa extensão trata-se de nada mais que o acréscimo de uma nova partícula ao modelo, um lépton neutro que não interage por força fraca. Essa partícula é chamada de neutrino estéril. Portanto, acrescentando um ou mais neutrinos estéreis ao Modelo Padrão posso obter a matriz de mistura para léptons e, consequentemente, contar o número de parâmetros físicos que ela possui. O interesse em contar esses parâmetros reside no fato de que encontrar o número de fases complexas presentes na matriz de mistura é equivalente a encontrar o número de fases de violação de simetria conjugação de carga e paridade (CP) para léptons. Em 1967, o físico russo Andrei Sakharov propôs uma forma de explicar a assimetria bariônica (matéria-antimatéria) partindo de um estado simétrico. Para isso, algumas condições precisariam ser respeitadas pela física do universo. Uma dessas condições é que exista na natureza uma fonte de violação CP. Procurar essa violação em léptons foi o objetivo deste trabalho. Assim, foi possível obter a matriz de mistura para léptons estendendo o modelo padrão pela adição de um neutrino estéril e levando em conta o caso geral de n famílias de léptons. Uma vez tendo encontrado a matriz de mistura, fizemos a contagem dos parâmetros. Além abranger os cálculos usados para encontrar o número de fases complexas damatriz, a dissertação apresenta uma breve introdução à teoria quântica de campos, a simetrias discretas e ao mecanismo de quebra espontânea de simetria, conceitos necessários para o entendimento do trabalho realizado
Abstract: The neutrino oscillation phenomenum, already experimentally observed, can only be explained if neutrino masses are different from zero. However, till recently, it was believed that neutrinos were massless. The Standard Model of elementary particles is yet not able to describe the massive nature of neutrinos, such that the lepton mixing matrix (between gauge eigenstates and mass eigenstates), analogous to the quark mixing matrix, can still not be found. Through a small extension of the Standard Model, it is possible to describe physics that take into account these masses and, therefore, provides us with these mixing matrices. This extension is nothing but the addition of a new particle, a neutral lepton that does not interact through weak force. This particle is called sterile neutrino. So, by adding one or more sterile neutrinos to the Standard Model, I can get the lepton mixing matrix and consequently count the number of physical parameters that it presents. The interest in counting these parameters resides in the fact that finding the number of complex phases in the mixing matrix is equivalent to finding the number of charge conjugation-parity (CP) violation for leptons. In 1967, the Russian physicist Andrei Sakharov proposed a way to explain the baryonic asymmetry (matter-antimatter) beginning with a symmetric state. For that to work some conditions needed to be respected by the universe physics. One of them is that there must exist in nature a source of CP violation. Looking for that source as the leptonic sector of the particle physics was the goal of this project. And finally it was possible to get the lepton mixing matrix extending the standard model by the addition of one sterile neutrino and taking into account the general case of n lepton families. Once we got the mixing matrix, we counted the physical parameters. Besides presenting all the calculation used for finding the number of complex phases in the matrix, this thesis presents a brief introduction to quantum field theory, discrete symmetries and the spontaneous symmetry breaking mechanism, all of these concepts being necessary for the understanding of the work accomplished
Mestrado
Física
Mestra em Física