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1
BELFATTO, BENEDETTA. « Flavour problems and new physics at TeV scale ». Doctoral thesis, Gran Sasso Science Institute, 2020. http://hdl.handle.net/20.500.12571/10042.
Texte intégralRésumé :
There is no explanation in the Standard Model for the replication of fermion families, neither for the mass hierarchy between them nor for the structure of the Yukawa coupling matrices, which remain arbitrary. The key towards under- standing the fermion masses and mixing pattern can be in symmetry principles. Masses of fermions can actually have a dynamical origin, following the spon- taneous symmetry breaking of gauge “horizontal" symmetries unifying families, differently acting on left and right species. U(3) or SU(3) “horizontal" family symmetries seem an intuitive hypothesis to be considered. Fermion masses should be induced by higher order operators containing flavon scalars emerging from renormalizable interactions via ‘universal seesaw’ mechanism after integrat- ing out some heavy fields, scalars or verctor-like fermions. Then in this case the fermion mass hierarchy and mixing among families can be related to the pat- tern of spontaneous breaking of the gauge SU(3) symmetry. The corresponding gauge bosons have flavor-nondiagonal couplings to fermions which in principle can induce flavour changing phenomena. In this case strong lower limits on the flavor symmetry breaking scales are expected. However, for special choices of horizontal symmetries there is a natural suppression of flavour changing effects due to a custodial symmetry. So gauge bosons can have mass in the TeV range, without contradicting the existing experimental limits.
However an unexpected anomaly shows up in quark mixing. After the recent high precision determinations of Vus and Vud, the first row of the CKM matrix is about 4σ deviated from unitarity.
The existence of the gauge symmetry SU(3)l acting between lepton families can recover unitarity if the symmetry is broken at a scale of about 6 TeV. In fact the gauge bosons of this symmetry contribute to muon decay in interference with the Standard Model, so that the Fermi constant is slightly smaller than the muon decay constant and unitarity is restored.
Alternatively, extra vector-like quarks can be thought as a solution to the CKM unitarity problem. The extra species should exhibit a large mixing with the first family in order to recover unitarity, then their mass should be no more than 6 TeV or so. The implications of the existence of so large mixing must be examined, in order to understand if it can actually exist without contradiction with experimental results on flavour changing neutral current processes and Standard Model observables. In principle an extra weak isodoublet can solve all the discrepancies between independent determinations of the CKM elements in the first row. However not all the discrepancies can be entirely recovered with- out contradicting experimental constraints. Then the existence of two or more
vector-like doublets or a vector-like isodoublet with a down-type or up-type isos- inglet can be considered. In these scenarios unitarity can be resettled and flavour changing can be avoided by setting to zero some couplings of extra species with Standard Model families.
If the anomalies in the determination of CKM mixing angles are confirmed by future experiments with greater precision, there might be strong indication towards the existence of physics beyond the Standard Model at the TeV scale, such as flavour changing gauge bosons and vector-like fermions with masses of few TeV. This new physics can be testable at next runs of high luminosity LHC or, more effectively, in future accelerators.
2
Lucente, Michele. « Implication of Sterile Fermions in Particle Physics and Cosmology ». Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112210/document.
Texte intégralRésumé :
Le mécanisme de génération de masses des neutrinos, la nature de la matière noire et l’origine de l’asymétrie baryonique de l’Univers sont les trois questions les plus pressantes dans la physique moderne des astroparticules, qui exigent l’introduction d’une nouvelle physique au-delà du Modèle Standard. Dans cette thèse, nous nous concentrons sur ces trois questions en fournissant une solution possible en termes d'une extension minimale du Modèle Standard, constituée par l’ajout d'un ensemble de fermions stériles au contenu des champs de la théorie. Les fermions stériles sont des champs qui sont singlets de jauge et qui peuvent interagir avec les neutrinos actifs à travers des termes de mélange. Nous nous concentrons sur le mécanisme dit de l’Inverse Seesaw (ISS), qui est caractérisé par une faible échelle de la nouvelle physique (de l’ordre TeV ou inférieure) et qui peut être testé dans les installations expérimentales actuelles et futures. Nous présentons l'analyse qui permet d’identifier les réalisations minimales de ce mécanisme et l'étude phénoménologique pour prendre en compte la masses des neutrinos légers et pour imposer toutes les contraintes expérimentales pertinentes au modèle, ainsi que les signatures expérimentales attendues. Nous montrons la viabilité de l’hypothèse que les neutrinos stériles constituent la matière noire, et les caractéristiques de cette solution dans le mécanisme minimale de l’ISS. La possibilité d’expliquer avec succès l'asymétrie baryonique à travers un processus de leptogenèse dans une réalisation testable du mécanisme est aussi adressée. Il est important de chercher des manifestations des fermions stériles dans les expériences de laboratoire. Nous abordons ce point en faisant des prévisions sur les rapports des branchement attendus pour les désintégrations des bosons vectoriels qui violent le saveur leptonique, qui peuvent être véhiculés par les fermions stériles. Nous étudions aussi l'impact des fermions stériles sur les fits globaux des données de précision électrofaibleThe neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We show the viability of the sterile neutrino hypothesis as dark matter component, together with the characteristic features of this scenario in the minimal Inverse Seesaw mechanism. The possibility of successfully accounting for the baryon asymmetry in a testable realisation of the leptogenesis mechanism is also addressed.On the other side it is important to look for manifestations of sterile fermions in laboratory experiments. We address this point by making predictions for the expected rates of rare lepton number violating decays of vector bosons, that can be mediated by sterile fermions, as well as by studying the impact of sterile fermions on global fit of electroweak precision data
3
Özer, Alp Deniz. « SO(10)-Grand Unification and Fermion Masses ». Diss., lmu, 2005. http://nbn-resolving.de/urn:nbn:de:bvb:19-46957.
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Bloch, Jacques Christophe Rodolphe. « Numerical investigation of fermion mass generation in QED ». Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5173/.
Texte intégralRésumé :
We investigate the dynamical generation of fermion mass in quantum electrodynamics (QED). This non-perturbative study is performed using a truncated set of Schwinger-Dyson equations for the fermion and the photon propagator. First, we study dynamical fermion mass generation in quenched QED with the Curtis-Pennington vertex, which satisfies the Ward-Takahashi identity and moreover ensures the multiplicative renormalizability of the fermion propagator. We apply bifurcation analysis to determine the critical point for a general covariant gauge. In the second part of this work we investigate the dynamical generation of fermion mass in full, unquenched QED. We develop a numerical method to solve the system of three coupled non-linear equations for the dynamical fermion mass, the fermion wavefunction renormalization and the photon renormalization function. Much care is taken to ensure the high accuracy of the solutions. Moreover, we discuss in detail the proper numerical cancellation of the quadratic divergence in the vacuum polarization integral and the requirement of using smooth approximations to the solutions. To achieve this, we improve the numerical method by introducing the Chebyshev expansion method. We apply this method to the bare vertex approximation to unquenched QED to determine the critical coupling for a variety of approximations. This culminates in the detailed, highly accurate, solution of the Schwinger-Dyson equations for dynamical fermion mass generation in QED including both, the photon renormalization function and the fermion wavefunction renormalization in a consistent way, in the bare vertex approximation and, for the first time, using improved vertices. We introduce new improvements to the numerical method, to achieve the accuracy necessary to avoid unphysical quadratic divergences in the vacuum polarization with the Ball-Chiu vertex.
5
Bhatti, Abdul Aziz. « Fermion masses and Higgs Physics in Grand Unified Theories ». Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-114132.
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6
Therrien, Eric. « Fermion masses and mixing in a simple composite model ». Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63874.
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7
Guillaume, Alexandre. « Transitions de phases dans les fermions lourds sous contrainte uniaxiale ». Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10060.
Texte intégralRésumé :
Nous presentons les premiers resultats obtenus avec un dispositif experimental permettant de changer la contrainte uniaxiale continument a tres basse temperature. Le principe de l'appareil consiste a controler la pression d'helium appliquee sur un soufflet metallique connecte thermiquement a la boite de melange d'un refrigerateur a dilution. Nous etudions l'effet de la contrainte uniaxiale, appliquee selon l'axe c du compose tetragonal uru#2si#2. Nous trouvons que la temperature de transition supraconductrice t#c varie de facon parabolique en fonction de la contrainte #c avec une pente de 76 mk/kbar a #c = 0 kbar et une pente nulle a 6. 5 kbar. La temperature de transition antiferromagnetique t#n varie lineairement en fonction de la contrainte avec une pente egale a 32 mk/kbar. Nous rapportons les premieres mesures de l'evolution du gap des excitations de la phase antiferromagnetique en fonction de la contrainte uniaxiale selon l'axe c. Il decroit lineairement avec une pente de 0. 63 k/kbar. Grace aux mesures de champ critique, nous donnons la premiere estimation de la croissance de la masse effective avec la contrainte selon l'axe c, m*(6. 5 kbar) = 1. 07 m*(0 kbar). Pour le compose hexagonal upt#3, nous confirmons que la temperature de transition supraconductrice t#+#c decroit, d'abord avec une pente de 14. 71. 5 mk/kbar, pour une contrainte appliquee suivant l'axe c inferieure a 2 kbar puis decroit, avec une pente de 5. 20. 7 mk/kbar, pour des contraintes superieures. En variant de 0 a 8. 4 kbar la contrainte #a appliquee selon l'axe a, nous trouvons que la temperature t#+#c decroit regulierement avec une pente de 2. 00. 7 mk/kbar. A partir de l'evaluation du coefficient a de la loi = #0+at#2 et de la pente du second champ critique a bas champ, nous trouvons que la masse effective augmente avec la contrainte suivant l'axe c et diminue avec la contrainte suivant l'axe a:m*(#c = 6. 5 kbar) = 1. 26 m*(#c = 0 kbar) ; m*(#a = 6. 5 kbar) = 0. 86 m*(#a = 0 kbar).
8
de, Medeiros Varzielas Ivo. « Family symmetries and the origin of fermion masses and mixings ». Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497464.
Texte intégral
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Allanach, Benjamin Christopher. « Supersymmetric extensions of the standard model and the fermion mass problem ». Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294624.
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Wu, Jackson M. S. « Improvement of Wilson fermions and twisted mass lattice QCD / ». Thesis, Connect to this title online ; UW restricted, 2005. http://hdl.handle.net/1773/9706.
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11
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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12
Brunton, Rosalind Elizabeth. « Strong correlation effects in heavy fermion and double exchange systems ». Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300345.
Texte intégral
13
Gomes, Adriano Doff Sotta. « Alguns aspectos sobre a geração dinâmica de massa em modelos de Technicolor / ». São Paulo : [s.n.], 2005. http://hdl.handle.net/11449/102510.
Texte intégralRésumé :
Orientador: Adriano A. NataleBanca: Paulo Sérgio Rodrigues da Silva
Banca: Carlos Ourívio Escobar
Banca: Vicente Pleitez
Banca: Juan Carlos Montero Garcia
Resumo: O mecanismo de Higgs baseado na existência de um bóson escalar fundamental apresenta problemas de hierarquia e naturalidade. Neste trabalho revisitamos os aspectos mais gerais associados a modelos de Technicolor. Em particular, argumentamos que a auto-energia fermiônica deveria apresentar a forma conhecida como Irregular, a qual resolve a maioria dos problemas enfrentados por modelos que seguem esta linha. No último capítulo desta tese elaboramos um modelo, assumindo como solução a forma Irregular para a auto-energia fermiônica, onde as três gerações de férmions adquirem massa via efeitos de quebra dinâmica de simetria.
Abstracts: The Higgs mechanism, based on existence of fundamental scalars bosons suffer from the hierarchy and naturalness problems. In this work we review the main aspects of the Technicolor models. In particular, we aegue that the fermionic self-energy must behave as the Irregular form, that solve most of the Technicolor models problems. In the last Chapter of his thesis we build a model, assuming the Irregular form for the fermionic self-energy, where the three fermionic generations receive mass dynamically.
Doutor
14
Harrington, A. P. « Enhanced masses and superconductivity in highly correlated fermionic systems ». Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233549.
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15
Dück, Alexander [Verfasser], et Werner [Akademischer Betreuer] Rodejohann. « Phenomenology of Neutrinos and Possible SO(10) Origins of Fermion Masses and Mixings / Alexander Dück ; Betreuer : Werner Rodejohann ». Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1177148234/34.
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16
Drach, Vincent. « Fermions twistés dynamiques et spectroscopie des baryons ». Phd thesis, Université de Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00633497.
Texte intégralRésumé :
Ce travail s'intéresse au calcul de la masse des baryons à partir de la théorie décrivant l'interaction forte : la chromodynamique quantique (QCD). Cette théorie régit l'interaction entre les quarks et l es gluons et a pu durant ces dernières décennies être vérifiée à haute énergie grâce à l'une de ses propriétés : la liberté asymptoti que. Celle-ci prédit que les calculs perturbatifs sont valides à haute énergie car la constante de couplage tend vers zéro. Les quantités physiques régissant la physique à basse énergie nécessitent quant à elles un traitement non pertubatif et font l'objet de ce travail. La seule approche con nue permettant de calculer ces observables en contrôlant tous les effets systématiques est la QCD sur réseau. Le C hapitre 1 est une introduction au formalisme de la QCD et à sa formulation discrétisée. Le second chapitre est dédié à la discréti sation particulière utilisée au sein de la collaboration Europan Twisted Mass (ETM). Le Chapitre 3 met en place la technologie nécessaire au calcul des masses des hadrons. L'estimation des intégrales fonctionnelles en utilisant le calcul massi vement parallèle sur des Super Calculateurs est décrite dans le Chapitre 4. La production de configurations de jauge sur ce type d'architecture constitue une part importante du travail effectué durant cette thèse. Le Chapitre 5 est dédié à la formulation des théories effectives dites de pertubations chirales. Les Chapitres 6 et 7 sont consacrés aux baryons légers et étranges. Les eff ets systématiques ainsi que les extrapolations chirales sont largement discutés.
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Harraud, Pierre-Antoine. « Etude de la structure du nucléon par des calculs de QCD sur réseau avec des fermions de masse twistée ». Phd thesis, Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00546526.
Texte intégralRésumé :
La compréhension de la structure interne du nucléon à partir de la ChromoDynamique Quantique est un enjeu majeur de la physique hadronique. Seule la QCD sur réseau permet d'évaluer numériquement les observables à partir des principes ab-initio. Le sujet de cette thèse est l'étude des facteurs de forme du nucléon et le premier moment des fonctions de distributions de partons en utilisant une action discrétisée avec des fermions de masse twistée. Cette dernière a l'avantage de supprimer les effets de discrétisation au premier ordre en la maille du réseau. D'autre part, l'ensemble des simulations permet un contrôle accru des erreurs systématiques. Après avoir détaillé les techniques de calcul utilisées, je présenterai les résultats obtenus pour un large éventail de paramètres, mailles de réseau variant entre 0.056 fm et 0.089 fm, volumes compris entre 2.1 et 2.7 fm et masses de pions dans le domaine 260-470 MeV. La constante de renormalisation vectorielle a ainsi été obtenue dans le secteur du nucléon avec une grande précision. Pour le rayon de charge électrique, les effets de volume fini mis en évidence fournissent une clef pour expliquer sa dépendance chirale vers le point physique. Les résultats pour le moment magnétique et axial, les fractions d'impulsion et d'hélicité portées par les quarks, ne présentent pas d'effets de discrétisation ni de volume fini significatifs. Aux masses de pions considérées, leurs valeurs montrent une déviation par rapport aux valeurs expérimentales, leur comportement chiral n'exhibant pas la courbure prédite par les perturbations chirales qui permettrait de résoudre ce désaccord apparent.
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Montefiori, Samuele. « Anomalies in the stress tensor of a chiral fermion in a gauge background ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18793/.
Texte intégralRésumé :
In this thesis we study the anomalies of a chiral fermion in a gauge background, using a different regularization from those already present in literature.
The aim here is to study all the anomalies involving the stress tensor. The final motivation is to eventually focus on the trace anomaly, which has been of some interest recently.
Thus, after a brief introduction to the issue of anomalies in QFT, we proceed by studying the symmetries of a massless left-handed Weyl fermion coupled to an abelian gauge background and to gravity as well (used as an external source for the stress tensor).
The regularization of the corresponding QFT is then implemented through Pauli-Villars (PV) fields having a Dirac mass.
Particular emphasis is put on the unusual mass term used at this stage, consisting of a customary Dirac mass multiplied by the vierbein determinant e raised to the generic power a.
After devoting a chapter to the mathematical tool of the heat kernel, we restrict ourselves to flat space, present the regulators of the model, the "jacobians" associated to each of its symmetries, and all the useful heat kernel coefficients needed for the anomaly calculations.
Finally, we evaluate all the anomalies of our model: the usual chiral anomaly and the anomalies in the stress tensor, namely the trace anomaly, the anomaly in the symmetry of the stress tensor (the local Lorentz anomaly), and the anomaly in the conservation of the stress tensor (the gravitational anomaly).
The latter is the most demanding task, as it requires the use of particular heat kernel coefficients which have been rarely treated in literature.
The calculation of all these anomalies is the leading task accomplished in this thesis.
Of course, one does not expect all these anomalies to be genuine, as some are expected to be canceled by the variation of local counterterms, leaving at the end only the chiral and trace anomalies with their known expression.
That this is the case is left for future research.
19
Tsang, Justus Tobias. « Continuum limit of D and Ds decay constants with Moebius domain wall fermions at physical pion masses ». Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/405419/.
Texte intégralRésumé :
The inclusion of heavy quarks, such as the charm quark, poses difficulties in Lattice QCD simulations. These need to be overcome in order to make predictions of hadronic observables including a charm quark such as the decay constants fD and fDs. We first establish the region of validity of simulating heavy quarks with domain wall fermions (DWFs) in a feasibility study. We then carry out dynamical simulations with RBC/UKQCD’s Nf = 2+1f ensembles at three lattice spacings (a −1 = 1.73 − 2.77 GeV) including two physical pion mass ensembles. From this we make a prediction for the decay constants fD and fDs and, using experimental input, the corresponding CKM matrix elements. In the first part of this work we investigate the suitability of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. We generate four quenched QCD gauge ensembles with the tree-level improved Symanzik gauge action and inverse lattice spacings in the range 2.0 − 5.7 GeV. On these we carry out an exploratory study to identify a region in the DWF parameter space that displays minimal cut-off effects. We find this region for the domain wall height M5 = 1.6 allowing for bare heavy quark masses satisfying amh <∼ 0.4, independent of the lattice spacing. Below this limit we maintain desirable features of DWF such as approximate chiral symmetry and O(a)-improvement. Based on this, we carry out a detailed scaling study of the decay constants of heavy-strange pseudoscalar mesons and the dispersion relation of heavy-heavy and heavy-strange pseudoscalar mesons. We find mild a2 discretisation effects for the heavy-strange decay constants and the heavy-strange dispersion relation. The cut-off effects for the heavy-heavy pseudoscalar dispersion relation are somewhat more pronounced. On our ensembles we find a 4 effects for heavy masses beyond the charm quark mass and large momenta (|p| ∼ 1.6 GeV). The findings of the pilot study establish the basis for simulations of charm quarks with domain wall fermions. In the second part of the presented work we simulate heavy-light and heavy-strange pseudoscalar mesons on RBC/UKQCD’s 2 + 1f ensembles with pion masses as low as 139 MeV and inverse lattice spacings ranging from 1.73 GeV to 2.77 GeV. From this data we extract the decay constants fD and fDs. We devise two different fit ansatze to process this data and carry out a full systematic error analysis. We find fD = 208.7(2.8)stat (+2.1−1.8)sys MeV, fDs = 246.4(1.9)stat (+1.3−1.9)sys MeV and fDs/fD = 1.1667(77)stat (+60−46)sys. Finally, using experimental input we extract the corresponding CKM matrix elements. We find |V|cd = 0.2185(50)exp. (+35−37)lat and |V |cs = 1.011(16)exp. (+11− 9)lat where the first error comes from the experimental input and the second from our determination of the decay constants. We compare our results with the existing literature and find good agreement between our central values and competitive errors. This work constitutes the basis of RBC/UKQCD’s wider charm physics program.
20
Mollet, Simon. « Exploration of 6-dimensional models with non trivial topology and their predictions for fermions masses and mixings, neutrino physics, flavour changing interactions and CP violation ». Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/230863.
Texte intégralRésumé :
In this thesis, we study several scenarios which go beyond the Standard Model of particle physics with the aim of gaining a better understanding for the multiplication of fermion families, their masses and mixings pattern and its relation to CP violation. The common feature of the models we envisaged (and the guiding principle of the thesis) is the introduction of extra space dimensions. In a first attempt to explain the fermion mass structure, we elaborate on a model with two extra-dimensions and a Nielsen- Olesen vortex background established on it. In this framework, three families in 4D can be seen as different modes of a single generation in 6D, while their extra-dimensional wavefunctions turn out highly constrained by the dynamics, which allows to determined the mass matrices with few parameters. Moreover, with a few additional hypotheses only, it is possible to simultaneously account for the striking differences between neutrinos and charged fermions. After a summary of the model, we illustrate this with the explicit formulation of a benchmark model which reproduces convincingly all the mass and mixing parameters of the Standard Model, taking advantage of new, more precise numerical solutions of the field equations, and including the recent measurements of the Standard Model scalar boson mass and of the neutrino heta_13 mixing angle (the latter has however been correctly predicted by the model before its first measurement). We then turn to the predictions which mainly concern the neutrino and gauge sectors. In the former, we remind the Majorana nature, and the natural tendency for inverted hierarchy pattern with an almost maximally suppressed neutrinoless double beta decay. On the other hand, we predict new (neutral) gauge bosons whose couplings to fermions are not flavour-diagonal but are however constrained (in their strength and their flavour structure) by the 6D anatomy of the theory. We compare their detectability in precision low energy processes and at colliders (especially at the LHC), and show that in the simplest geometries at least, the bounds from the former exclude interesting phenomenology for the latter. Nevertheless, we turn to more phenomenological effective Lagrangians with the same overall structure and in which we are able to lower the mass scale of the new bosons to a reachable energy, and thus analyse the possible signatures for LHC.In the last part of this work, we turn to the issue of CP violation and show how in certain 6D models with non simply connected topologies, it is possible to generate a non negligible CP violation at the 4D level in a pure gauge approach. We carefully study how the 4D CP symmetry is related to particular transformations of the original 6D theory and subsequently show how an incompatibility of such transformations with the compactification scheme can lead to an effective CP breaking. As a proof of concept, we build a toy model with two extra-dimensions compactified on a flat torus and end in 4D with a light neutral fermion with a non zero electric dipole moment.Dans cette thèse, nous étudions plusieurs scénarios au-delà du Modèle Standard de la physique des particules à la recherche d'une meilleure compréhension de la multiplication des familles de fermions, de leurs masses et de leurs mélanges, ainsi que la relation à laviolation de CP.La caractéristique commune à tous les modèles envisagés (et le concept sous-jacent à toute la thèse) est l'introduction de nouvelles dimensions spatiales. Dans une première tentative pour expliquer le spectre des fermions, nous développons un modèle où une structure de vortex à la Nielsen-Olesen est établie sur deux dimensions supplémentaires. Dans ce cadre, les trois familles à 4D peuvent être vues comme différents modes d'une unique génération à 6D, tandis que leur fonctions d'onde extra-dimensionnelles s'avèrent fortement contraintes par la dynamique ;ceci permet d'établir les matrices de masses en terme d'un petit nombre de paramètres. De plus, grâce à quelques hypothèses additionnelles seulement, il est possible de justifier simultanément les différences marquées entre neutrinos et fermions chargés. Nous synthétisons le modèle et l'illustrons en en formulant une réalisation particulière qui parvient à reproduire de manière convaincante tous les paramètres de masse et de mélange du Modèle Standard. Pour l'occasion, nous exploitons de nouvelles solutions aux équations des champs, numériquement plus précises, et prenons en compte les mesures récentes de la masse du boson scalaire et de l'angle de mélange heta_13 pour les neutrinos (le modèle avait cependant prédit ce dernier avant qu'il ne soit mesuré pour la première fois). Nous nous tournons ensuite vers les prédictions du modèle et qui concernent principalement le secteur des neutrinos et celui des bosons de jauge. Pour le premier, nous rappelons la nature "Majorana" des neutrinos, ainsi que la tendance naturelle à une hiérarchie inverse avec une suppression quasi maximale de la double désintégration bêta sans neutrino. D'autre part, nous prédisons de nouveaux bosons de jauge (neutres) dont les couplages aux fermions ne sont pas diagonaux dans l'espace des saveurs mais sont contraints (autant en terme de valeurs qu'en termes de structure) par l'anatomie de la théorie à 6D. Nous comparons leurs détections potentielles dans les processus de précision à basse énergie et auprès des collisionneurs (en particulier au LHC). Nous montrons que, dans les géométries les plus simples du moins, les limites imposées par les premiers excluent toute phénoménologie intéressante du côté des seconds. Toutefois, en nous tournantvers des Lagrangiens effectifs qui conservent la même structure d'ensemble mais ouvrent à une étude plus phénoménologique, nous sommes capables de réduire l'échelle de masse de ces nouveaux bosons jusqu'à une énergie accessible, et donc d'en analyser de potentielles signatures au LHC.Dans la dernière partie de ce travail, nous nous intéressons à la question de la violation de CP et montrons comment dans certains modèles à 6D avec une topologie non-simplement connexe, il est possible de générer une violation de CP non négligeable à 4D dans une approche de "pure jauge". Nous étudions attentivement comment la symétrie CP à 4D est reliée à des transformations particulières de la théorie originale à 6D, suite à quoi nous montrons comment l'incompatibilité de ces transformations avec la façon dont sont "compactifiées" les dimensions supplémentaires peut conduire à une brisure effective de CP. Pour illustrer la faisabilité de notre approche, nous élaborons un "modèle jouet" où deux dimensions supplémentaires sont compactifiées sur un tore plat, et obtenons à 4D un fermion neutre léger et qui possède un moment électrique dipolaire non nul.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Zeidlewicz, Lars [Verfasser], Owe [Akademischer Betreuer] Philipsen et Gernot [Akademischer Betreuer] Münster. « The thermal transition of quantum chromodynamics with Twisted Mass Fermions / Lars Zeidlewicz. Gutachter : Owe Philipsen ; Gernot Münster ». Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2011. http://d-nb.info/1043947493/34.
Texte intégral
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Gomes, Adriano Doff Sotta [UNESP]. « Alguns aspectos sobre a geração dinâmica de massa em modelos de Technicolor ». Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/102510.
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O mecanismo de Higgs baseado na existência de um bóson escalar fundamental apresenta problemas de hierarquia e naturalidade. Neste trabalho revisitamos os aspectos mais gerais associados a modelos de Technicolor. Em particular, argumentamos que a auto-energia fermiônica deveria apresentar a forma conhecida como Irregular, a qual resolve a maioria dos problemas enfrentados por modelos que seguem esta linha. No último capítulo desta tese elaboramos um modelo, assumindo como solução a forma Irregular para a auto-energia fermiônica, onde as três gerações de férmions adquirem massa via efeitos de quebra dinâmica de simetria.
Abstracts: The Higgs mechanism, based on existence of fundamental scalars bosons suffer from the hierarchy and naturalness problems. In this work we review the main aspects of the Technicolor models. In particular, we aegue that the fermionic self-energy must behave as the Irregular form, that solve most of the Technicolor models problems. In the last Chapter of his thesis we build a model, assuming the Irregular form for the fermionic self-energy, where the three fermionic generations receive mass dynamically.
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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.
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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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Hepburn, Derek John. « Light hadron spectrum, quark masses and meson decay constants from lattice QCD with O(a)-improved dynamical Wilson fermions ». Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/15009.
Texte intégralRésumé :
In this thesis I present results for the light hadron spectrum, light quark masses and meson decay constants from numerical simulations of lattice QCD. The simulations were performed on a 163 x 32 space-time lattice using the standard Wilson gauge field action and a fully O(a)-improved Sheikholeslami-Wohlert fermion action with Nj = 2 degenerate flavours of dynamical fermions. A subset of these simulations were performed at fixed lattice spacing, as determined through the Sommer scale parameter, ro, in order to investigate the effects associated with a finite sea quark mass whilst keeping cutoff and finite size effects fixed. A quenched simulation was also performed at this lattice spacing for comparative purposes. No clear evidence of unquenching was found in the light hadron spectrum at the quark masses used in the matched simulations studied here. Light quark masses were determined from chiral extrapolations of pseudoscalar and vector meson masses to both the standard and PCAC definitions of the quark mass. The bare strange quark mass was fixed through the K, K* and ø meson masses for comparison. Renormalised quark masses have been determined in the ? scheme at a reference scale of 2GeV with matching performed at two values of the scale parameter, m = 1/a and m = p/a, in order to study the systematic effects.
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Pricopi, Lucia. « Etude de la masse effective des fermions lourds CeAl2 et CeRu2Si2 par mesures de l'effet de Haas-van Alphen sous champs magnétiques pulsés ». Toulouse 3, 2001. http://www.theses.fr/2001TOU30044.
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Pientka, Grit. « Hadronic corrections to electroweak observables from twisted mass lattice QCD ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17312.
Texte intégralRésumé :
Für verschiedene Richtgrößen, die untersucht werden, um Hinweise auf Neue Physik jenseits des Standardmodells der Teilchenphysik zu finden, stellt die Gitter-QCD stellt derzeit den einzigen Ab-initio-Zugang für die Berechnung von nichtperturbativen hadronischen Beiträgen dar. Zu diesen Observablen gehören die anomalen magnetischen Momenten der Leptonen und das Laufen der elektroschwachen Kopplungskonstanten. Wir bestimmen den führenden QCD-Beitrag zum anomalen magnetischen Moment des Myons mit Hilfe einer Gitter-QCD-Rechnung auf Ensemblen, die Nf=2+1+1 dynamische Twisted-Mass-Fermionen berücksichtigen. Durch die Betrachtung aktiver up, down, strange and charm Quarks können erstmalig Gitter-QCD-Daten für die Myonanomalie direkt mit phänomenologischen Resultaten verglichen werden, da letztere bei der derzeitigen Genauigkeit sensitiv auf die ersten beiden Quarkgenerationen sind. Unlängst wurde darauf hingewiesen, dass es auch möglich sein könnte Beiträge Neuer Physik durch verbesserte Messungen der anomalen magnetischen Momente des Elektrons und des Tauons nachzuweisen. Aus diesem Grund berechnen wir auch deren führende QCD-Beiträge, was gleichzeitig eine Überprüfung des Wertes für das Myon liefert. Zusätzlich nutzen wir die gewonnenen Daten, um den führenden hadronischen Beitrag zum Laufen der Feinstrukturkonstante zu berechnen. Darüber hinaus zeigen wir, dass sogar für den schwachen Mischungswinkel der führende QCD-Beitrag mit Hilfe dieser Daten berechnet werden kann. Dadurch identifizieren wir eine neue grundlegende Observable für die Suche nach Neuer Physik, deren hadronische Beiträge mit Hilfe der Gitter-QCD beschafft werden können. Mit den Resultaten dieser Arbeit ist es uns gelungen ungeeignete Herangehensweisen der phänomenologisch notwendigen Flavourseparation auszuschließen und somit direkt die derzeit präziseren phänomenologischen Bestimmungen dieser bedeutsamen physikalischen Größe zu unterstützen.For several benchmark quantities investigated to detect signs for new physics beyond the standard model of elementary particle physics, lattice QCD currently constitutes the only ab initio approach available at small momentum transfers for the computation of non-perturbative hadronic contributions. Among those observables are the lepton anomalous magnetic moments and the running of the electroweak coupling constants. We compute the leading QCD contribution to the muon anomalous magnetic moment by performing lattice QCD calculations on ensembles incorporating Nf=2+1+1 dynamical twisted mass fermions. Considering active up, down, strange, and charm quarks, admits for the first time a direct comparison of the lattice data for the muon anomaly with phenomenological results because both the latter as well as the experimentally obtained values are sensitive to the complete first two generations of quarks at the current level of precision. Recently, it has been noted that improved measurements of the electron and tau anomalous magnetic moments might also provide ways of detecting new physics contributions. Therefore, we also compute their leading QCD contributions, which simultaneously serve as cross-checks of the value obtained for the muon. Additionally, we utilise the obtained data to compute the leading hadronic contribution to the running of the fine structure constant, which enters all perturbative QED calculations. Furthermore, we show that even for the weak mixing angle the leading QCD contribution can be computed from this data. In this way, we identify a new prime observable in the search for new physics whose hadronic contributions can be obtained from lattice QCD. With the results obtained in this thesis, we are able to exclude unsuitable phenomenologically necessary flavour separations and thus directly assist the presently more precise phenomenological determinations of this eminent quantity.
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Delplace, Pierre. « Etats de bord et cônes de Dirac dans des cristaux bidimensionnels ». Paris 11, 2010. http://www.theses.fr/2010PA112354.
Texte intégralRésumé :
Cette thèse en physique constitue une étude théorique des états de bord dans des cristaux bidimensionnels qui exhibent deux cônes de Dirac (dégénérés en spin) dans leur relation de dispersion. Les deux systèmes considérés sont le graphène d'une part, et le réseau carré traversé d'un demi quantum de flux magnétique d'autre part. L'accent est mis sur la description analytique des niveaux d'énergie dispersifs sous fort champ magnétique (régime de l'effet Hall quantique), à l'approche du bord. Selon la géométrie du réseau cristallin et la forme du bord considéré, différents types de couplage sont induits sur les composantes de la fonction d'onde, donnant lieu à des structures d'états de bord différentes mais qui peuvent néanmoins être décrites de façon communes. En l'absence de champ magnétique, des états de bord peuvent également exister dans ces systèmes, mais ceux-ci ont une origine différente et leur existence même dépend de la nature des bords. Dans le cas du graphène, on montre comment comprendre l'existence de tels états en terme d'une phase de Berry particulière, appelée phase de Zak. Cette approche permet entre autre de comprendre comment manipuler ces états de bord en induisant une transition topologique de la phase de Zak à partir des paramètres de volume. Un autre type de transition topologique est également étudié. Il s'agit de la fusion des cônes de Dirac dans le réseau carré à demi flux. On montre que le mécanisme donnant lieu à ce phénomène est totalement différent de celui connu dans le graphène, et que le voisinage de la transition peut toutefois être décrit avec le même Hamiltonien effectif. Une partie plus courte traite de la localisation faible sur un cylindre désordonné en présence d'interactions électroniques. Le but de cette étude est d'illustrer le rôle de la géométrie sur les mécanismes de décohérence dus aux interactions électron-électron dans les systèmes diffusifs. Les harmoniques de la correction de localisation faible alors calculées mettent en évidence différents régimes qui permettent de sonder les différentes échelles de longueur caractérisant la décohérence. Ces longueurs révèlent la sensibilité des processus cohérents à la géométrie, et sont caractérisées par des lois de puissance en température spécifiquesThis thesis in physics constitutes a theoretical study of the edge states in bi-dimensional crystals which exhibit two Dirac cones (spin degenerated) in their dispersion relation. The two systems considered are graphene and the square lattice with half a magnetic quantum flux per plaquette. The analytical description of the dispersive energy levels in a high magnetic field (quantum Hall effect regime) due to the presence of edges is highlighted. According to the geometry of the crystal lattice and the shape of the edge, different kinds of coupling are induced between the components of the wave function. This gives rise to various structures of edge sates which however can be described in a common way. Without any magnetic field, some edge states can also exist in these systems, but they have a different origin and their existence itself depends on the shape of the edge. In the case of graphene, we show how to connect the existence of these edge states with a particular type of Berry phase, the so-called Zak phase. This approach allows, for instance, to understand how to manipulate these edge states by tuning the bulk parameters, what involves a topological transition of the Zak phase. Another type of topological transition has also been studied. It consists in the merging of the Dirac cones in the square lattice with half a quantum flux. We show that the mechanism leading to such a phenomena strongly differs from the one known in graphene, and that the physics around the transition can however be described within the same effective Hamiltonian. A shorter second part deals with the weak localization on a disordered cylinder with electronic interactions. The aim of this study is to illustrate the role of the geometry in the decoherence mechanisms due to electron-electron interactions in diffusive systems. The harmonics of the weak localization correction calculated reveal different regimes which probe the different length scales characterizing the decoherence. These lengths underline the sensibility of coherent processes to the geometry and are characterized by specified power laws in temperature
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Rogério, Rodolfo José Bueno [UNESP]. « Aspectos clássicos e quânticos de espinores de dinânima não-usual : espinores de dimenssão de massa um ». Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/158276.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Na presente tese apresentaremos de forma detalhada o estudo sistemático de uma teoria quântica com férmions de dimensão de massa um que obedecem as estatísticas de Fermi-Dirac, abordando essencialmente sua construção, quantização do campo, análise dos observáveis físicos e aplicações quânticas. Forneceremos todos os detalhes de uma descoberta teórica inesperada da partícula de spin $1/2$ que compõe um conjunto completo de autoespinores com helicidade dual do operador conjugação de carga. Esses espinores recebem o nome de Elko, um acrônimo proveniente do Alemão \textit{Eigenspinoren des Ladungskonjugationsoperators}. Veremos que o elo entre os espaços de representação $(1/2, 0)$ e $(0, 1/2)$ não é dado pela simetria de paridade mas sim pela ``Mágica das matrizes de Pauli'', e, portanto, como consequência a dinâmica de tais campos será regida única e exclusivamente pela dinâmica de Klein-Gordon. Tal fato faz com que o propagador associado ao Elko guarde muita similaridade com o propagador do campo escalar. Intrinsicamente, em sua formulação embrionária, as somas de spin para o Elko mostram um termo que quebra explicitamente a covariância relativística, levando então à apreciação da \textit{Very Special Relativity}, que nada mais é do que um subgrupo do grupo de Lorentz, cuja álgebra deixa as somas de spin invariantes ou covariantes. Entretanto, mostraremos que existe uma liberdade na definição da estrutura dual, a qual permite que seja construída uma teoria local e invariante por transformações de Lorentz, levando, assim, a uma nova física bastante interessante e promissora.
The present thesis covers in details a systematic study of a quantum theory based on mass dimension one fermions which satisfy the Fermi-Dirac statistics, essentially addressing its construction, field quantization, analysis of physical observables and quantum applications. We provide all the details of an unexpected theoretical discovery of a spin 1/2 particle which composes a complete set of dual helicity spinors of the charge conjugation operator. Such spinors are called Elko, an acronym for the German word Eigenspinoren des Ladungskonjugationsoperators. We show that the relation between the representation spaces (1/2,0) and (0,1/2) is given by the “Magic of Pauli matrices” rather than parity symmetry, therefore, as a consequence the dynamic of such fields is governed solely and exclusively by the Klein-Gordon dynamic. Such fact makes the Elko propagator to be very similar to the scalar field propagator Intrinsically, in its embryonic formulation, Elko spin sums shows up a term that explicitly breaks relativistic covariance, leading to the appreciation of Very Special Relativity, a theory which is based on a subgroup of the Lorentz group, whose algebra leaves the spin sums invariant or covariant. However, we show a freedom in the dual structure definition, which allows the construction of a local and Lorentz invariant theory, thus, leading to a very interesting and promising new physics
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Deppisch, Thomas Ludwig [Verfasser], et U. [Akademischer Betreuer] Nierste. « A Tale of Scales - Fermion Masses and Mixing in Minimal Supersymmetric SO($_10}$) and Resummation of Gluino Contributions to the MSSM Higgs Potential / Thomas Ludwig Deppisch ; Betreuer : U. Nierste ». Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1187343366/34.
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Cavalcante, Everton. « Decaimento do próton e massa dos léptons numa extensão de gauge do modelo padrão ». Universidade Federal da Paraíba, 2011. http://tede.biblioteca.ufpb.br:8080/handle/tede/5700.
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Previous issue date: 2011-03-30Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this dissertation we will approach the lepton and barion number simmetries as low energy manifestation of more fundamental theories at higher energies. By using effective operators we investigate the possibility of generating reasonable mass terms for leptons as well as suppressed proton lifetime in the Standard Model. We also look at the proton decay processes in a specific grand unified theory (the minimal SU(5)) and comment about the experimental bounds on proton lifetime from Superkamiokande. Finally, we consider a simple gauge extension of Standard Model, the minimal SUC(3) SUL(3) UN(1) model, pointing some drawbaces in this model concerning lepton masses and proton lifetime. We study how it is possible to diminish its scalar content and solve the lepton mass and proton decay issues.
Nesta dissertação abordaremos as simetrias de número bariônico e leptônico do modelo padrão como manifestações em baixas energias de teorias mais fundamentais. Por meio de operadores efetivos, estudaremos termos de massa para léptons e modos de decaimento para o próton. Também estudaremos a predição quanto ao tempo de decaimento do próton num modelo de grande unificação específico (modelo SU(5) mínimo), comparando com o limite experimental do Super-Kamiokande. Por último apontaremos alguns problemas numa extensão de gauge do modelo padrão (modelo SUC(3) SUL(3) UN(1) mínimo), diminuindo seu conteúdo de campos escalares, onde os operadores efetivos para massa dos léptons e decaimento do próton serão manipulados através da introdução de certas simetrias discretas.
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Almutairi, Alanoud. « Electronic band structure equations and Fermi surface evolution from 2D materials to 3D layered superconducting compounds ». Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134414/1/Alanoud%20Mulfi%20Z_Almutairi_Thesis.pdf.
Texte intégralRésumé :
A simple approach for extracting the superconducting gap of materials from trendline fittings of key sections of their Electronic Band Structures (EBS), calculated using Density Functional Theory (DFT), is presented. The proposed approach works well for very different compositions, structure types and superconducting transition temperatures, indicating that it is robust, reliable and versatile. This approach provides many advantages in terms of required computational time and power, compared with similar information extracted from phonon dispersion calculations, making it accessible to wider DFT-computational chemistry and physics communities. The approach also identifies requirements for superconductivity and indirectly contributes towards understanding of superconductivity mechanisms.
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Weiland, Cedric. « Effects of fermionic singlet neutrinos on high- and low-energy observables ». Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00922999.
Texte intégralRésumé :
In this doctoral thesis, we study both low- and high-energy observables related to massive neutrinos. Neutrino oscillations have provided indisputable evidence in favour of non-zero neutrino masses and mixings. However, the original formulation of the Standard Model cannot account for these observations, which calls for the introduction of new Physics. Among many possibilities, we focus here on the inverse seesaw, a neutrino mass generation mechanism in which the Standard Model is extended with fermionic gauge singlets. This model offers an attractive alternative to the usual seesaw realisations since it can potentially have natural Yukawa couplings (O(1)) while keeping the new Physics scale at energies within reach of the LHC. Among the many possible effects, this scenario can lead to deviations from lepton flavour universality. We have investigated these signatures and found that the ratios R_K and R_π provide new, additional constraints on the inverse seesaw. We have also considered the embedding of the inverse seesaw in supersymmetric models. This leads to increased rates for various lepton flavour violating processes, due to enhanced contributions from penguin diagrams mediated by the Higgs and Z bosons. Finally, we also found that the new invisible decay channels associated with the sterile neutrinos present in the supersymmetric inverse seesaw could significantly weaken the constraints on the mass and couplings of a light CP-odd Higgs boson.
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Buttazzo, Dario. « Implications of the discovery of a Higgs boson with a mass of 125 GeV ». Doctoral thesis, Scuola Normale Superiore, 2013. http://hdl.handle.net/11384/85868.
Texte intégralRésumé :
The discovery of a Higgs-like particle by the ATLAS and CMS experiments at the LHC
has been a major event for particle physics. The rather precise knowledge of the mass of
the Higgs boson and of its couplings to the other Standard Model elds has important
consequences for the physical phenomena taking place at the Fermi scale of electroweak
symmetry breaking. We will analyze some of these implications in the most motivated
frameworks for physics at that scale { supersymmetry, models of a composite Higgs boson,
and the Standard Model itself.
At the same time, precision experiments in
avour physics require a highly non-generic
structure of
avour and CP transitions. This is relevant to any model of electroweak
symmetry breaking with a relatively low scale of new phenomena, motivated by naturalness,
where some mechanism has to be found in order to keep unwanted
avour e ects
under control. We will discuss in particular the consequences of the approximate U(2)3
symmetry exhibited by the quarks of the Standard Model.
The combined analysis of the indirect constraints from
avour, Higgs and electroweak
physics will allow us to outline a picture of some most natural models of physics at the
Fermi scale. This is particularly interesting in view of the forthcoming improvements in
the direct experimental investigation of the phenomena at that energies. Although non
trivially, a few models emerge that look capable of accommodating a 125 GeV Higgs
boson, consistently with all the other constraints, with new particles in an interesting
mass range for discovery at the LHC, as well as associated
avour signals.
Finally, the measurement of the last parameter of the Standard Model { the Higgs quartic
coupling { has important consequences even if no new physics is present close to the Fermi
scale: its near-critical value, which puts the electroweak vacuum in a metastable state
close to a phase transition, may have an interesting connection with Planck-scale physics.
We derive the bound for vacuum stability with full two-loop precision and use it to explore
some possible scenarios of near-criticality.
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Taylor, Paul Andrew. « Nuclear Binding Energy in Terms of a Redefined (A)symmetry Energy ». Thesis, Boston College, 2004. http://hdl.handle.net/2345/460.
Texte intégralRésumé :
Thesis advisor: Kevin S. BedellWe investigate the structure of the equation of state of finite nuclear matter by examining the nature of isospin dependence in the (a)symmetry energy term. In particular, we include in the description of the binding energy fourth-order dependence with respect to the asymmetry factor, (N-Z)/A, and the regime of the l=0 Landau parameter, F0´ , is required to be less than –1. This modified equation predicts a minimum binding energy where N≠Z, in addition to the standard symmetric minimum when N=Z. Results with the new asymmetry energy term are compared with experimental binding and symmetry energies from standard semi-empirical mass formulas. Importantly, this method reveals one possible mechanism for producing the phenomenon of neutron excess which is seen in physical nuclei
Thesis (BS) — Boston College, 2004
Submitted to: Boston College. College of Arts and Sciences
Discipline: Physics
Discipline: College Honors Program
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Pagano, Emanuele Vincenzo. « Space-time correlations of intermediate mass fragments emitted in Heavy ion reactions at Fermi energy by intensity interferometry studied with CHIMERA and perspectives ». Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3984.
Texte intégralRésumé :
In Heavy Ion Collisions (HIC) at Fermi energies (E/A between 10 MeV/nucleon and 100 MeV/nucleon) hot nuclear systems are produced and they may disassemble by a variety of dynamical and statistical mechanisms with vastly different time scales (neck emission, fission, multifragmentation, fusion-evaporation, ecc.). The study of the Space-Time properties of the emission pattern of the particles produced in the reactions represents one the most challenge topics of the modern investigation in nuclear physics. For this reason special geometrically flexible particle-particle correlation arrays are powerful tools to be used in coincidence mode with a 4pi detectors. Sensitivity to both space-time and spectroscopic properties of nuclear systems produced in HIC needs accurate measurements of both high angular and energy resolution over a large solid angle coverage. One of these arrays is FARCOS, presently under construction at the INFN Sezione di Catania and LNS. The FARCOS (Femtoscope ARray for COrrelations and Spectroscopy) consists of a number of twenty telescopes, each composed by two Double Sided Silicon Strip Detectors (DSSSD), of thickness 300 micron and 1500 micron, respectively, followed by four CsI(Tl) crystals of 6 cm of thickness read-out by silicon photodiodes. In this PhD thesis a report of the experimental characteristics of the FARCOS array is presented. In particular, tests with alpha sources and on-beams measurements coming from the recent experiment INKIISSY are discussed. A basic study of the particle-particle correlation function is also an important step of this large experimental effort in order to characterize the time scale of the reaction in different experimental configurations. In this work, the space-time sensitivity of the fragment-fragment Correlation Function to the emission of Intermediate Mass Fragments (the IMFs have atomic number between 3 and 25) has been investigated. In particular, IMF-IMF correlation function methods have been applied to 124Sn+64Ni at E/A= 35 MeV reverse kinematics reactions for the physics case of dynamical and statistical fission processes. The IMF-IMF correlation function shows good sensitivity in order to disentangle between dynamical and statistical processes. Some comparisons between data and theoretical simulations, are also discussed.
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Rasmussen, Rasmus Westphal. « Implications of physics beyond the Standard Model in the quark and lepton sectors ». Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19174.
Texte intégralRésumé :
Das Standardmodell (SM) der Teilchenphysik hat sich in der Praxis als vielseitige Theorie bewährt, dennoch deuten nichtverschwindende Neutrinomassen, dunkle Materie und Baryonenasymmetrie auf Physik jenseits des SM (BSM) hin. Um also ein mit den Beobachtungen konsistentes Modell zu entwickeln, ist eine umfassendere Theorie nötig. Experimentell kann entweder in Abweichungen von den Vorhersagen des SM nach neuer Physik gesucht werden. So kann jedes BSM-Szenario getestet werden.
In dieser Arbeit werden BSM-Szenarien im Quark- sowie im Leptonen-Sektor und deren phänomenologische Konsequenzen auf messbare Observablen betrachtet. Ein konkretes Beispiel in dieser Dissertation sind Neutrino massen modellierung mit der Einführung von sterilen Neutrinos. Wir untersuchen die phänomenologische Konsequenz ihrer Einführung auf verschiedenen Massenskalen im Zusammenhang mit symmetriegenerierten oder strukturlosen Neutrinomassenmodellen. Unter den geschmacksabhängigen aktivsterilen Mischungen in den durch Symmetrie erzeugten Massenmodellen finden wir deutliche Hierarchien, die als Modelldiskriminator für zukünftige Experimente dienen.
Ähnlich wie beim Ausnutzen von Symmetrien im Neutrinosektor, kann man Symmetrien auch in Modellen für Quarkmassen nutzen. In dieser Arbeit werden Symmetrien behandelt, die den Cabibbo-Winkel für Quarkmischung in führender Ordnung quantisieren können. Dies führt zu einer Vielzahl möglicher Symmetrien, welche genutzt werden können um spezifische Modelle für Quarkmassen zu entwickeln.
BSM-Physik indirekt mit Hilfe astrophysikalischer Neutrinos zu testen stellt eine Alternative zur direkten Detektion dar, und führt bei Betrachtung der Zusammensetzung des NeutrinoFlavours zu klaren Abweichungen von den Erwartungen. Neben der Behandlung verschiedenster BSM-Szenarien wird auch das Potenzial zukünftiger Experimente betrachtet, vor Allem im Hinblick auf deren Effektivität Physik jense.The Standard Model (SM) of particle physics is a well-tested and predictive theory, however non-zero neutrino masses, the existence of dark matter, and the baryon asymmetry suggest physics beyond the SM. Thus, in order to have a model consistent with observations, a more complete theory is needed. Experimentally, one can search for new physics, thereby differentiate different BSM scenarios. We consider BSM scenarios in the quark and lepton sectors, and study their phenomenological consequence on measurable observables. A specific example is neutrino mass modeling with the introduction of sterile neutrinos. We study the phenomenological consequence of introducing them at different mass scales in the context of symmetry-generated or structureless neutrino mass models. We find distinct hierarchies among the flavor-dependent active-sterile mixings in the symmetry-generated mass models, which acts as a model discriminator for future experiments. Similarly as using symmetries in the neutrino sector, one can also use symmetries in quark mass models. This thesis consider symmetries capable of quantizing the Cabibbo quark mixing angle to leading order. As a result, a variety of possible symmetries are obtained, which can be used to build specific quark mass models. Probing BSM physics indirectly via astrophysical neutrinos, acts as an alternative to direct detection, and using the neutrino flavor composition as observable, BSM physics leads to clear deviations from expectation. Additional information comes from other effects, and it helps in constraining the parameter space further. Beside discussing different BSM scenarios, we illustrate the potential of future experiments, emphasizing their effectiveness to test and discriminate BSM physics.
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Resende, Bruno Messias Farias de. « Modelos matemáticos para isolantes topológicos em redes ». Universidade Federal de Uberlândia, 2017. http://dx.doi.org/10.14393/ufu.di.2018.90.
Texte intégralRésumé :
CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorSistemas descritos por Hamiltonianos do tipo Dirac são ubíquos. Surgindo em materiais como grafeno, isolantes topológicos ou recentemente nos semimetais de Weyl. Devido ao interesse tecnológico e acadêmico desses materiais, caracterizar suas propriedades é essencial. Uma abordagem matemática para efetuar o estudo de tais sistemas consiste em discretizar o Hamiltoniano no espaço das posições, mas tal abordagem esbarra no problema da duplicação de férmions. De forma breve, esse problema atesta pela impossibilidade de simulação de férmions livres não massivos em uma rede discreta sem que alguma simetria ou propriedade da Hamiltoniana seja quebrada. No presente trabalho demonstramos que tal problemática não deveria ser causa de preocupação para o estudo de sistemas na matéria condensada, pois podemos utilizar a simetria quebrada para confinar os portadores de carga no sistema para remover os estados duplicados. Tal remoção é conseguida com a inserção de um termo quadrático em relação ao momento, conhecido como massa de Wilson. Nesse sentido podemos inserir um termo de Wilson com quebra de simetria necessária para o confinamento, tornando o problema de duplicação de férmions irrelevante, essa relação não tinha sido notada até o presente trabalho, e recentes resultados na literatura erroneamente atribuem a massa de Wilson com a quebra de uma simetria de reversão temporal, o que não necessariamente é verdade. Nesse contexto além de abordar essa relação a presente dissertação objetiva também elucidar alguns mal entendimentos a respeitos das massas de Wilson, quiralidade e outras simetrias. Para validar nosso argumento central estudamos diversos sistemas de interesse e comparamos com os resultados na literatura.
Hamiltonians of Dirac type are ubiquitous. Appearing in materials such as graphene, topological insulators or recently in the Weyl semimetals. Due to the technological and academic interest of these materials, characterizing their properties is essential. A mathematical approach to study these systems consists of discretizing the Hamiltonian in the space of positions, but such an approach causes the problem of doubling fermions (FDP). We demonstrate the FDP should not be a cause of concern for the study of confined systems because we can use the broken symmetry to confine in the system to remove the duplicate states. Such removal is achieved by inserting a quadratic term with respect to the moment, known as the Wilson mass. In this sense we can insert a Wilson term with symmetry breaking required for confinement, rendering the fermion duplication problem irrelevant, this relationship had not been noticed until the present work, and recent literature results erroneously attribute Wilson’s mass to break of a symmetry of time reversal, which is not necessarily true. In this context, in addition to addressing this relationship, the present dissertation also aims to elucidate some misconceptions regarding the Wilson masses, chirality and other symmetries. In order to validate our central argument we study several systems of interest and compare it with the results in the literature.
Dissertação (Mestrado)
39
Dann, Martin Richard. « Experimental study of two dimensional fluid and solid '3He adsorbed on preplated graphite ». Thesis, Royal Holloway, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325525.
Texte intégralRésumé :
The heat capacity of 3He adsorbed on Grafoil (exfoilated graphite) preplated with four layers of 4He was measured between 1 and 50mK. The heat capacity was found to be linear up to 4OmK. At 3He surface densities below 4nm-2 two dimensional Fermi liquid behaviour was found and values of the hydrodynamic effective mass and Landau parameter Ff inferred. Subsequent steps in the heat capacity as a function of coverage were taken as evidence of independent 2D Fermi fluids. A low field DC SQUID pulsed NMR spectrometer was developed for future studies of magnetic order in 2D solid 3He films at ultralow temperatures
40
Nalpas, Laurent. « Propriétés et Modes de désexcitation des noyaux chauds observés dans la réaction 36Ar sur 58Ni avec le détecteur INDRA ». Phd thesis, Université Paris Sud - Paris XI, 1996. http://tel.archives-ouvertes.fr/tel-00083951.
Texte intégralRésumé :
Les collisions d'ions lourds aux énergies de Fermi conduisent à la formation de noyaux chauds. Selon l'énergie d'excitation mise en jeu, plusieurs modes de décroissance sont observés, en particulier une émission de fragments complexes (Z>2), dont l'origine est encore mal comprise.
Le GANIL permet d'explorer sur une large gamme en énergie, entre 32 et 95 MeV/u, la fonction d'excitation du système Ar+Ni depuis l'« évaporation » jusqu'à la «vaporisation » complète des noyaux chauds en particules légères (neutrons, isotopes de H, He).
L'analyse des mécanismes de réaction a montré, pour des petits paramètres d'impact, la domination des collisions binaires très inélastiques.
Ces dernières ont motivé une analyse en deux sources, des événements bien mesurés par le détecteur INDRA, à l'aide d'une méthode de reconstruction fondée sur l'«arbre minimum».
Des énergies d'excitation voisines de 20 MeV/A sont atteintes, à 95 MeV/u, dans les collisions centrales.
Pour les collisions violentes, le partage de l'énergie n'est plus équilibrée entre les deux partenaires, le quasiprojectile ayant une énergie d'excitation par nucléon plus élevée que la quasi-cible.
Entre 2 et 8 MeV/A d'énergie d'excitation totale du système, correspond une phase de production importante de fragments de masses intermédiaires qui sature autour de 10 MeV/A.
Le déclin du régime de «multifragmentation», au-delà de 15 MeV/A, coïncide avec la probabilité croissante d'observer la «vaporisation» des deux noyaux chauds, dont le seuil se situe aux environs de 8 MeV/A.
Par ailleurs, l'augmentation régulière de la température extraite des rapports isotopiques He-Li en fonction de l'énergie d'excitation du quasi-projectile suggère une évolution progressive des modes de décroissance des noyaux chauds, en accord avec les prédictions de modèles statistiques.
Aucun signe d'une transition de phase du premier ordre de type liquide-gaz n'est observé pour ces noyaux légers.
41
Lam, Yek Wah. « Isospin symmetry breaking in sd shell nuclei ». Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14446/document.
Texte intégralRésumé :
Dans cette thèse, nous avons développé une approche microscopique de la description des effets de la brisure de symétrie d’isospin dans les noyaux de la couche sd. Le travail est effectué dans le cadre du modèle en couches.Nous avons ajouté à un Hamiltonien nucléaire traditionnel, qui conserve l’isospin, l’interaction de Coulomb et le potentiel de type Yukawa d'échange de mésons pour modéliser les forces nucléaires dépendantes de la charge. La base de données sur les coefficients expérimentaux de l'équation des multiplets de masse isobariques (IMME) a été mise au point dans le cadre de cette thèse et a été utilisée pour ajuster les paramètres de l’hamiltonien. L'hamiltonien ainsi construit fournit une description théorique très précise du mélange d’isospin dans les états nucléaires. Nous montrons la pertinence de cette approche dans deux applications importantes : (i) le calcul des amplitudes d'émission de proton interdites par isospin, essentiels dans le cadre d’astrophysique nucléaire et (ii) le calcul de corrections (dues au mélange d'isospin) aux transitions bêta superpermises du type Fermi, cruciales pour les tests des symétries fondamentales du Modèle Standard de l’interaction électrofaibleIn the thesis, we develop a microscopic approach to describe theisospin-symmetry breaking effects in sd-shell nuclei.The work is performed within the nuclear shell model.A realistic isospin-conserving Hamiltonian is supplementedby a charge-dependent part consisting of the Coulomb interaction andYukawa-type meson exchange potentials to model charge-dependent forces ofnuclear origin. The extended database of the experimental isobaric mass multiplet equation coefficients is compiled during the thesis work and is used in a fit of the Hamiltonian parameters.The constructed Hamiltonian provides an accurate theoretical description ofthe isospin mixing nuclear states. A specific behaviour of the IMME coefficients have been revealed.We present two important applications (i) calculations of isospin-forbiddenproton emission amplitudes, which is often of interest for nuclearastrophysics, and (ii) calculation on corrections to nuclear Fermi beta decay, which is crucial for the tests of fundamental symmetries of the weak interaction
42
Soddu, Andrea. « Models of fermion masses / ». 2003. http://wwwlib.umi.com/dissertations/fullcit/3091138.
Texte intégral
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« A bottom-up approach to fermion masses ». Université catholique de Louvain, 2008. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-12032008-232938/.
Texte intégral
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Ayyar, Venkitesh. « Fermion Mass Generation without Spontaneous Symmetry Breaking ». Diss., 2016. http://hdl.handle.net/10161/12855.
Texte intégralRésumé :
The conventional mechanism of fermion mass generation in the Standard Model involves Spontaneous Symmetry Breaking (SSB). In this thesis, we study an alternate mechanism for the generation of fermion masses that does not require SSB, in the context of lattice field theories. Being inherently strongly coupled, this mechanism requires a non-perturbative approach like the lattice approach.
In order to explore this mechanism, we study a simple lattice model with a four-fermion interaction that has massless fermions at weak couplings and massive fermions at strong couplings, but without any spontaneous symmetry breaking. Prior work on this type of mass generation mechanism in 4D, was done long ago using either mean-field theory or Monte-Carlo calculations on small lattices. In this thesis, we have developed a new computational approach that enables us to perform large scale quantum Monte-Carlo calculations to study the phase structure of this theory. In 4D, our results confirm prior results, but differ in some quantitative details of the phase diagram. In contrast, in 3D, we discover a new second order critical point using calculations on lattices up to size $ 60^3$. Such large scale calculations are unprecedented. The presence of the critical point implies the existence of an alternate mechanism of fermion mass generation without any SSB, that could be of interest in continuum quantum field theory.
Dissertation
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陳依婷. « Neutrino Masses Through Zee Mechanism in 5D Split Fermion Model ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/73124117256746341790.
Texte intégralRésumé :
碩士國立清華大學
物理學系
97
The phenomenon of neutrino oscillation implies that neutrinos have masses, and the flavor eigenbasis is not the mass eigenbasis, so neutrinos oscillate between different flavor states while traveling. Thus it is beyond the Standard Model, and it calls for new physics.Here we study the Zee model and Extra dimensions to explain the neutrino oscillation. First, suppose there exists a compactied fth dimension, and neutrinos have Ma jorana masses through the 5 dimensional Zee model. Second, assume the fermions are localized on a 4 dimensional brane embedded in the 5 dimensional space-time by the Split Fermion model, while the higgs are free to propagate along the extra dimension. We can get the forms of parameters in the neutrino mass matrix from Zee model. Then, transforming with the PMNS matrix, we found ranges of charged lepton masses, neutrino masses and mixing angles, and so on. Based on Anthropic Principle, we compare them to the experiment data, and we get 4 possible solutions. We also check the branch ratios of 5 lepton flavor violating processes, and they also satisfy the experiment constraints. Thus this is a possible model.
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Özer, Alp Deniz [Verfasser]. « SO(10) - grand unification and fermion masses / vorgelegt von Alp Deniz Özer ». 2005. http://d-nb.info/978062906/34.
Texte intégral
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Guo, Duo. « Fermion Low Modes in Lattice QCD : Topology, the η' Mass and Algorithm Development ». Thesis, 2021. https://doi.org/10.7916/d8-knph-2598.
Texte intégralRésumé :
Lattice gauge theory is an important approach to understanding quantum chromodynamics (QCD) due to the large coupling constant in the theory at low energy. In this thesis, we report our study of the topological properties of the gauge fields and we calculate 𝘮_η and 𝘮_η' which are related to the topology of the gauge fields. We also develop two algorithms to speed up the inversion of the Dirac equation which is computationally demanding in lattice QCD calculations.
The topology of lattice gauge fields is important but difficult to study because of the large local fluctuations of the gauge fields. In chapter 2, we probe the topological properties of the gauge fields through the measurement of closed quark loops, field strength and low-lying eigenvectors of the Shamir domain wall operator. The closed quark loops suggest the slow evolution of topological modes during the generation of QCD configurations. The chirality of the low-lying eigenvectors is studied and the lattice eigenvectors are compared to the eigenvectors in the continuous theory. The topological charges are calculated from the eigenvectors and the results agree with the topological charges calculated from the smoothed gauge fields. The fermion correlators are also obtained from the eigenvectors.
The non-trivial topological properties of QCD gauge fields are important to the mass of the η and η', 𝘮_η and 𝘮_η'. Lattice QCD is an area where 𝘮_{\eta}$ and 𝘮_{\eta'}$ can be calculated by using gauge fields that are sampled over different topological sectors. We calculate 𝘮_η and 𝘮_η' in chapter 3 by including the fermion correlators and the topological charge density correlators. The errors of 𝘮_η and 𝘮_η' are reduced to the percent level and the mixing angle between the octet, singlet states in the SU(3) limit and the physical eigenstates is calculated.
An algorithm that reduces communication and increases the usage of the local computational power is developed in chapter 4. The algorithm uses the multisplitting algorithm as a preconditioner in the preconditioned conjugate gradient method. It speeds up the inversion of the Dirac equation during the evolution phase.
In chapter 5, we utilize two lattices, called the coarse lattice and the fine lattice, that lie on the renormalization group trajectory and have different lattice spacings. We find that the low-mode space of the coarse lattice corresponds to the low-mode space of the fine lattice. Because of the correspondence, the coarse lattice can be used to solve the low modes of the fine lattice. The coarse lattice is used in the restart algorithm and the preconditioned conjugate gradient algorithm where the latter is called the renormalization group based preconditioned conjugate gradient algorithm (RGPCG). By using the near-null vectors as the filter, RGPCG could reduce the operations of the matrix multiplications on the fine lattice by 33% to 44% for the inversion of Dirac equation. The algorithm works better than the conjugate gradient algorithm when multiple equations are solved.
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Bhatti, Abdul Aziz [Verfasser]. « Fermion masses and Higgs physics in grand unified theories / submitted by Abdul Aziz Bhatti ». 2010. http://d-nb.info/1002224055/34.
Texte intégral
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Kaczmarczyk, Jan. « Unconventional superconductivity in correlated fermion systems ». Praca doktorska, 2011. https://ruj.uj.edu.pl/xmlui/handle/item/274855.
Texte intégralRésumé :
W rozprawie rozważono niekonwencjonalne nadprzewodnictwo w układach silnie skorelowanych elektronów w polu magnetycznym (typu Zeemana). Silne korelacje miedzy kwazicząstkami uwzględniono poprzez przybliżenie Gutzwillera w ramach statystycznie-konsystentnego podejścia zaproponowanego ostatnio w naszym zespole. Poddano analizie sytuacje gazu cienkich kwazicząstek i otrzymano diagram fazowy w funkcji pola magnetycznego i temperatury (dla przypadku dwu i trój-wymiarowego oraz uwzględniając symetrie przerwy typu s-wave oraz d-wave). W niskich polach magnetycznych układ jest w stanie Bardeena-Coopera-Schrieffera (BCS), natomiast przy zwiększaniu pola magnetycznego następuje przejście do fazy typu Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) z niezerowym pędem środka masy par Coopera. Celem wyodrębnienia nowych cech przypadku z silnymi korelacjami, wyniki zostały porównane z otrzymanymi dla przypadku bez korelacji. We wszystkich analizowanych sytuacjach faza FFLO występuje w szerszym przedziale temperatur i pol w przypadku silnych korelacji co implikuje, ze silne korelacje stabilizują fazę FFLO (i prawdopodobnie inne niekonwencjonalne fazy pojawiające się w silnych polach i niskich temperaturach). W rozprawie wytłumaczono także mechanizm stabilizacji tego stanu. Przeanalizowano także przewodność złącza typu normalny metal - silnie-skorelowany nadprzewodnik w celu sformułowania eksperymentalnego testu naszych wyników. Przebiegi przewodności w przypadkach z obecnością i absencja silnych korelacji różnią się znacznie. Rojnice te powinny być łatwo mierzalne doświadczalnie, dostarczając testu występowania silnych korelacji w stanie nadprzewodzącym. Mianowicie, korelacje zmieniają odległość pomiędzy maksimami przewodności pochodzącymi od nośników o spinie w gorę i tych o spinie w dol. W sytuacji braku korelacji ta odległość jest równa podwojonej energii Zeemana. Dla przypadku z korelacjami, odległość ta jest 30-50% mniejsza, ale w innych modelach może tez być większa w zależności od szczegółów struktury elektronowej. Dodatkowo, rozwalono koegzystencję antyferromagnetyzmu (AF) i nadprzewodnictwa (SC) w ramach modelu t-J dla układu z silnymi korelacjami oraz w polu magnetycznym, w granicy Pauliego. Faza z koegzystencja wykazuje się dwiema przerwami: singletowa oraz przerwa trypletowa typu staggered-triplet. Składowa trypletowa charakteryzuje się niezerowym pędem środka masy par Coopera i możne być postrzegana jako analogon fazy FFLO. Otrzymano diagram fazowy w funkcji wypełnienia pasma i pola magnetycznego. Dla sytuacji pasma prawie do polowy wypełnionego nasze wyniki przypominają otrzymane ostatnio w układzie cieżkofermionowym $CeCo(In_{1-x}Cd_{x})_{5}$. Mianowicie, przy zwiększaniu pola magnetycznego układ ewoluuje z fazy z koegzystencja, poprzez fazę AF, ku spinowo-spolaryzowanemu stanowi normalnemu. Co więcej, pojawienie się przerwy nadprzewodzącej zmniejsza magnetyzację podsieci w stanie AF+SC.We study unconventional superconductivity in strongly correlated electron systems and in applied magnetic (Zeeman) field. The strong correlations among quasiparticles are accounted for by means of the Gutzwiller approximation within the statistically-consistent scheme proposed recently in our group. We analyze the situation for a gas of heavy quasiparticles and obtain a phase diagram on the magnetic field-temperature plane (for both two- and three-dimensional cases, including the s-wave- and d-wave-gap symmetry solutions). In low magnetic fields the system is in the Bardeen-Cooper-Schrieffer (BCS) phase, whereas for the increasing magnetic field a transition to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase with nonzero Cooper pair momentum takes place. To distinguish novel features of the case with strong correlations we compare our results with those for a noncorrelated situation. In all analyzed situations the FFLO phase is more robust for the case with strong correlations, which implies that strong correlations stabilize the FFLO phase (and possibly other high-field low-temperature unconventional phases). We explain the stabilization mechanism. Next, we study conductance of a normal metal - strongly-correlated superconductor junction in order to provide an experimental test of our results. The conductance spectra in the cases with and without strong correlations differ essentially, and the differences should be easily observable experimentally, providing a hallmark of strong correlations in the superconducting state. Namely, correlations alter the distance between the conductance peaks for carriers with spin-up and spin-down. In the non-correlated case this distance is twice the Zeeman energy. In the correlated case this distance is about 30-50% smaller, but in other models it may be larger, depending on details of the electronic structure. Additionally, we perform analysis of the coexistence of antiferromagnetism (AF) and superconductivity (SC) within t-J model for a system with strong correlations and in applied magnetic field in the Pauli limit. The coexisting phase exhibits two superconducting gaps (a consequence of the AF and SC coexistence): singlet and staggered-triplet. The triplet component has a nonzero Cooper pair momentum, and can be viewed as an analogue of the FFLO phase. We obtain a phase diagram on the band filling - magnetic field plane. For band filling close to unity (i.e., close to the half-filled band situation) our results resemble those obtained recently in the heavy fermion system $CeCo(In_{1-x}Cd_{x})_{5}$. Namely, with the increasing magnetic field the system evolves from the coexisting phase, through AF phase, towards the spin-polarized normal state. Moreover, the onset of superconducting order decreases antiferromagnetic magnetization.
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Urbach, Carsten [Verfasser]. « Wilson twisted mass fermions : towards realistic simulations of lattice QCD / Carsten Urbach ». 2006. http://d-nb.info/978606612/34.
Texte intégral