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1
Patt, Brian Lawrence. « Higgs family symmetry and supersymmetry ». Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36397.
Résumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 77-79).
In this thesis we investigate building models of family symmetry that give the Higgs fields family structure. We construct several models, starting with 2 generation models then moving onto 3 generation models. These models are described sequentially in chapters 2 through 6. All of these models are supersymmetric and they did not previously exists in the literature. In these models, quark (and lepton) masses and mixings are determined the vacuum expectation values of the family sector. These vacuum expectation values (VEV) can have a hierarchal structure because they correspond to flat directions of a superpotential. At low energies these models contain just one light pair of Higgs fields. Experimentally, the most interesting feature of these models are couplings between the low energy Higgs and moduli of the family sector. These couplings should be observable at the Large Hadron Collider.
by Brian Lawrence Patt.
Ph.D.
2
Jing, Li Ph D. Massachusetts Institute of Technology. « Physical symmetry enhanced neural networks ». Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/128294.
Résumé :
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, February, 2020
Cataloged from student-submitted PDF version of thesis
Includes bibliographical references (pages 91-99).
Artificial Intelligence (AI), widely considered "the fourth industrial revolution", has shown its potential to fundamentally change our world. Today's AI technique relies on neural networks. In this thesis, we propose several physical symmetry enhanced neural network models. We first developed unitary recurrent neural networks (RNNs) that solve gradient vanishing and gradient explosion problems. We propose an efficient parametrization method that requires [sigma] (1) complexity per parameter. Our unitary RNN model has shown optimal long-term memory ability. Next, we combine the above model with a gated mechanism. This model outperform popular recurrent neural networks like long short-term memory (LSTMs) and gated recurrent units (GRUs) in many sequential tasks. In the third part, we develop a convolutional neural network architecture that achieves logarithmic scale complexity using symmetry breaking concepts. We demonstrate that our model has superior performance on small image classification tasks. In the last part, we propose a general method to extend convolutional neural networks' inductive bias and embed other types of symmetries. We show that this method improves prediction performance on lens-distorted image
by Li Jing.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Physics
3
Yang, Xu. « Symmetry and topology in condensed matter physics : ». Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109160.
Résumé :
Thesis advisor: Ying RanRecently there has been a surging interest in the topological phases of matter, including the symmetry-protected topological phases, symmetry-enriched topological phases, and topological semimetals. This thesis is aiming at finding new ways of searching and probing these topological phases of matter in order to deepen our understanding of them. The body of the thesis consists of three parts. In the first part, we study the search of filling-enforced topological phases of matter in materials. It shows the existence of symmetry-protected topological phases enforced by special electron fillings or fractional spin per unit-cell. This is an extension of the famous Lieb-Schultz-Mattis theorem. The original LSM theorem states that the symmetric gapped ground state of the system must exhibit topological order when there's fractional spin or fractional electron filling per unit-cell. However, the LSM theorem can be circumvented when commensurate magnetic flux is present in the system, which enlarge the unit-cells to accommodate integer numbers of electrons. We utilize this point to prove that the ground state of the system must be a symmetry-protected topological phase when magnetic translation symmetry is satisfied, which we coin the name “generalized LSM theorem”. The theorem is proved using two different methods. The first proof is to use the tensor network representation of the ground state wave-function. The second proof consists of a physical argument based on the idea of entanglement pumping. As a byproduct of this theorem, a large class of decorated quantum dimer models are introduced, which satisfy the condition of the generalized LSM theorem and exhibit SPT phases as their ground states. In part II, we switch to the nonlinear response study of Weyl semimetals. Weyl semimetals (WSM) have been discovered in time-reversal symmetric materials, featuring monopoles of Berry’s curvature in momentum space. WSM have been distinguished between Type-I and II where the velocity tilting of the cone in the later ensures a finite area Fermi surface.To date it has not been clear whether the two types results in any qualitatively new phenomena. In this part we focus on the shift-current response ($\sigma_{shift}(\omega)$), a second order optical effect generating photocurrents. We find that up to an order unity constant, $\sigma_{shift}(\omega)\sim \frac{e^3}{h^2}\frac{1}{\omega}$ in Type-II WSM, diverging in the low frequency $\omega\rightarrow 0$ limit. This is in stark contrast to the vanishing behavior ($\sigma_{shift}(\omega)\propto \omega$) in Type-I WSM. In addition, in both Type-I and Type-II WSM, a nonzero chemical potential $\mu$ relative to nodes leads to a large peak of shift-current response with a width $\sim |\mu|/\hbar$ and a height $\sim \frac{e^3}{h}\frac{1}{|\mu|}$, the latter diverging in the low doping limit. We show that the origin of these divergences is the singular Berry’s connections and the Pauli-blocking mechanism. Similar results hold for the real part of the second harmonic generation, a closely related nonlinear optical response. In part III, we propose a new kind of thermo-optical experiment: the nonreciprocal directional dichroism induced by a temperature gradient. The nonreciprocal directional dichroism effect, which measures the difference in the optical absorption coefficient between counterpropagating lights, occurs only in systems lacking inversion symmetry. The introduction of temperature-gradient in an inversion-symmetric system will also yield nonreciprocal directional dichroism effect. This effect is then applied to quantum magnetism, where conventional experimental techniques have difficulty detecting magnetic mobile excitations such as magnons or spinons exclusively due to the interference of phonons and local magnetic impurities. A model calculation is presented to further demonstrate this phenomenon
Thesis (PhD) — Boston College, 2021
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
4
Tan, Jong Anly. « Extra dimensions and electroweak symmetry breaking ». W&M ScholarWorks, 2010. https://scholarworks.wm.edu/etd/1539623558.
Résumé :
In anticipation of the Large Hadron Collider (LHC) which is currently scheduled to start operating in September 2009, Particle physicists have developed various models to predict phenomena that may be observed in the LHC data. One of the ideas that have been developed is warped extra dimensions. The S parameter, one of the electroweak precision observables is predicted by experiments to be less than about 0.1. However, most of the models that try to explain the electroweak symmetry breaking without a Higgs Boson have a large S parameter > 0.2.;We study the possibility of reducing the S parameter in a wared extra dimensions scenario. In our models the S parameter is small over a significant region of the parameter space, and may be consistent with experimental bounds.;Since the extra dimensional models are an effective theory at low energy, we then explore the UV completion of extra dimensional models by latticizing the extra dimension. We study a class of supersymmetric models in which certain aspects of the low energy effective theory can be determined exactly. We find that the topology of the extra dimension is determined dynamically and does not always agree with the naive interpretation of the deconstructed model.
5
Da, Rold Leandro. « Symmetry breaking in particle physics from extra dimensions ». Doctoral thesis, Universitat Autònoma de Barcelona, 2006. http://hdl.handle.net/10803/3377.
Résumé :
Los principios de simetría han jugado un rol fundamental en la comprensión de la naturaleza. Sin embargo en general las simetrías no son exactas, sino que están rotas. El estudio de mecanismos de ruptura de simetrías es una de las áreas más activas de la física actual. En esta tesis se estudia la ruptura de simetrías en teorías con dimensiones extra. La motivación principal es que la física de dimensiones extra provee nuevos mecanismos de ruptura de simetrías. En particular se estudian la ruptura de la simetría quiral de QCD y la ruptura de la simetría electrodébil (EW) del Modelo Estandard (SM). En cuanto a la simetría quiral de QCD, se propone un modelo efectivo 5D que describe la ruptura quiral en el sector de mesones. Se describen los sectores escalar, pseudoescalar, vectorial y axial de mesones mediante un modelo en espacio curvo 5D. Como QCD en el límite de gran N se trata de un modelo de resonancias débilmente acopladas, motivo por el cual es posible realizar cálculos analíticos. Se predicen las masas, constantes de decaimientos y acoplamientos entre los mesones en términos de los parámetros 5D. También se calculan los parámetros del lagrangiano quiral de piones de QCD. Todas las predicciones coinciden con los resultados experimentales dentro del rango de validez del modelo. Las predicciones son robustas y algunas relaciones son consecuencia de la simetría gauge 5D.
En segundo lugar se estudia la ruptura de la simetría EW en un modelo con un Higgs compuesto en el marco de una teoría 5D en AdS. El modelo da una descripción realista del sector EW. La ruptura EW es un efecto dinámico debido principalmente a contribuciones del top. En una región grande del espacio de parámetros los observables de precisón EW son compatibles con sus cotas experimentales. Además, en el modelo, las desviaciones de la interacción Zbb respecto de las predicciones del SM están protegidas por una simetría. El modelo predice un Higgs liviano cuya masa está correlacionada con la masa de la resonancia fermiónica más ligera. El top Right es esencialmente una partícula compuesta, por lo que se esperan desviaciones respecto del SM en este sector.
Por último se presenta un método para calcular correcciones radiativas en teorías con dimensiones extra. El método es muy útil para separar contribuciones finitas y divergentes.
Symmetry is at the basis of our knowledge of nature. It has been one of the most powerful tools to build our present understanding in theoretical physics. However, there are many symmetries that are only partially observed in nature, they are broken. Much of the current research is directly related with the study and comprehension of symmetry breakdown. This thesis is devoted to the study of symmetry breaking in theories with extra dimensions. In particular we study the breakdown of the chiral symmetry of quantum chromodynamics (QCD) and the breakdown of the electroweak (EW) symmetry of the Standard Model (SM).
We propose a 5D model to study the chiral symmetry breaking of QCD in the meson sector, in particular the vector, axial-vector, scalar and pseudoscalar. Alike large N QCD this is a model of weakly coupled resonances, we are able to do analytical calculations. We compute the spectrum, decay constants and interactions between the mesons in terms of the 5D parameters of the model. The model also predicts the constants of the low-energy chiral lagrangian of QCD, the quark masses and other physical quantities. We show that, within the range of validity of our model, all the predictions are in good agreement with the experimental results. The predictions are robust under modifications of the metric in the IR and some of the relations arise as a consequence of the 5D gauge symmetry.
We describe the EW symmetry breakdown in a composite Higgs model in the framework of a 5D theory. The model is fully realistic and the EW symmetry is broken dynamically by top loop effects. In a large region of the parameter space the EW precision observables are below their experimental bounds. The deviations of the interaction Zbb form the predictions of the SM are protected by a symmetry. Since the 5D model is weakly coupled we are able to compute the Higgs potential. The Higgs mass is small and it is correlated with the mass of the lightest fermionic resonance. The top right is mostly composite and we expect deviations from the SM in this sector.
As most of the calculations have been made at tree level, we develop a winding mode formalism to compute radiative corrections in theories with extra dimensions. The method is very useful to separate finite from divergent contributions.
6
Ng, Gim Seng. « Aspects of Symmetry in de Sitter Space ». Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11443.
7
Wang, Chong Ph D. Massachusetts Institute of Technology. « Entangling symmetry and topology in correlated electrons ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99286.
Résumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 213-224).
In this thesis, I study a class of exotic quantum matter named Symmetry-Protected Topological (SPT) phases. These are short-range-entangled quantum phases hosting non-trivial states on their boundaries. In the free-fermion limit, they are famously known as Topological Insulators (TI). Huge progress has been made recently in understanding SPT phases beyond free fermions. Here I will discuss three aspects of SPT phases in interacting systems, mostly in three dimensions: (1) Novel SPT phases could emerge in strongly correlated systems, with no non-interacting counterpart. In particular, I will discuss interaction-enabled electron topological insulators, including their classification, construction, characterization and realization. (2) When strong interactions are present, the surface of many SPT phases (including the familiar free fermion topological insulator) can be gapped without breaking any symmetry, at the expense of having intrinsic topological order on the surface. (3) Some topological phases that are non-trivial in the free fermion theory become trivial once strong interactions are introduced. The material of this thesis closely parallels that of Refs. [1, 2, 3, 4, 5, 6].
by Chong Wang.
Ph. D.
8
Lee, Allen S. M. Massachusetts Institute of Technology. « Symmetry-breaking motility and RNA secondary structures ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34396.
Résumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 61-64).
This thesis contains work on three separate topics: the spontaneous motility of functionalized particles, the designability of RNA secondary structures, and the statistical mechanics of homopolymer RNAs. For the work on spontaneous motility, we were motivated by in vitro experiments investigating the symmetry-breaking motility of functionalized spherical beads to develop a general theory for the dynamics of a rigid object propelled by an active process at its surface. Starting from a phenomenological expansion for the microscopic dynamics, we derive equations governing the macroscopic velocities of the object near an instability towards spontaneous motion. These equations respect symmetries in the object's shape, with implications for the phase behavior and singularities encountered at a continuous transition between stationary and moving states. Analysis of the velocity fluctuations of such an object reveals that these fluctuations differ qualitatively from those of a passive object. For the work on designability, we investigated RNA folding within a toy model in which RNA bases come in two types and complementary base pairing is favored. Following a geometric formulation of biopolymer folding proposed in the literature, we represent RNA sequences and structures by points in a high-dimensional "contact space." Designability is probed by investigating the distribution of sequence and structure points within this space. We find that one-dimensional projections of the sequence point distribution approach normality with increasing RNA length N.
(cont.) Numerical comparison of the structure point distribution with a Gaussian approximation generated by principal component analysis reveals discrepancies. The third and final project concerns the statistical mechanics of homopolymer RNAs. We compute the asymptotics of the partition function Zn and characterize the crossover length scale governing its approach to its leading asymptotic behavior. Consideration of restricted partition functions in which one or more base pairs are enforced leads to an interesting connection with ideal Gaussian polymers. We introduce the notion of gapped secondary structures and analyze the partition function Z?,) for RNAs of length n with gap at p. Another length scale emerges whose scaling agrees with that of the crossover scale found earlier.
by Allen Lee.
S.M.
9
Johnson, Samuel Buck. « Enhanced gauge symmetry in 6D F-theory ». Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104507.
Résumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 142-153).
This thesis reports on progress in understanding the set of 6D F-theory vacua. F-theory provides a strikingly clean correspondence between physics and physical quantities and mathematics and geometrical quantities, which allows us to make precise mathematical statements using well defined and understood methods. We present two related results that both serve the following principal goal: to understand the set of 6D F-theory vacua using geometrical methods, and then to compare these to low-energy supergravities. In doing so, we find a near-perfect correspondence between low-energy supergravities that can be obtained from F-theory and field theories that satisfy known low-energy consistency conditions, e.g. anomaly cancellation. However, we will also isolate several cases that we prove can never arise in F-theory yet have no visible lowenergy inconsistencies. The results are presented in two chapters. First, we describe a complete, systematic enumeration of all elliptically fibered Calabi-Yau threefolds (EF CY3s) with Hodge number h²,¹ >/= 350; physically, this classifies all F-theory models that lead to low-energy supergravities with >/= 351 neutral hypermultiplets. This result is obtained using global geometric calculations in finitely many, specific geometries. Second, we classify which local geometrical structures, corresponding to combinations of gauge algebras and (potentially shared) matter, can arise in F-theory. This classification is performed using local geometric calculations. This investigation reveals an exceedingly tight correspondence between F-theory models and consistent low-energy supergravities. Indeed, this near-perfect agreement provides a backdrop against which discrepancies between F-theory and low-energy supergravities stand out in sharp contrast. We describe in detail these discrepancies, in which seemingly consistent field theories cannot be described in F-theory. This work has several implications. First, it further refines the understanding of 6D supergravity models in F-theory, which has implications for string universality in 6D. It adds a level of mathematical precision to the study of 6D superconformal field theories (SCFTs) begun in [4, 3], which is a conjecturally complete classification of all 6D SCFTs. Our analysis confirms many of their results, but also explicitly shows that some of their proposed models cannot in fact be realized through their construction. Since our results can be phrased in terms of geometry, they also have implications for the study of EF CY3s. Finally, we discuss the subset of our results that hold in 4D F-theory as well, where they provide additional structure in a still difficult-to-constrain landscape.
by Samuel Buck Johnson.
Ph. D.
10
Chakrabarty, Ayan. « Brownian Motion of Low Symmetry Colloidal Particles ». Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1397786396.
11
Marshall, Gardner Rush. « Supersymmetric Leptophilic Models of Electroweak Symmetry Breaking ». W&M ScholarWorks, 2012. https://scholarworks.wm.edu/etd/1539623607.
Résumé :
Over the years, the Standard Model has proved itself to be an extremely durable theory. In spite of its success, very few empirical clues have emerged about the nature of the electroweak symmetry breaking that lies at its heart. With results from the LHC around the corner, this will hopefully change soon. In this dissertation we examine several possibilities for electroweak symmetry breaking and discuss various extensions to the Standard Model to resolve known problems. We begin by providing a brief overview of electroweak symmetry breaking, two Higgs doublet models, and supersymmetry. We then present a supersymmetric model that allows for small, Dirac neutrino masses. We find that it yields dramatic multi-lepton signatures, which have extremely small backgrounds. Next we discuss the leptophilic two Higgs doublet model and construct its supersymmetric analogue. Bounds on this model as well as its phenomenology are presented. We then show that an extension of this model includes a dark matter candidate that is capable of explaining a possibly observed excess of gamma-rays coming from the Galactic Center.
12
Abdelhady, A. M. H. H. « Scattering in soliton models and crossing symmetry ». Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71664.
Résumé :
Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Crossing symmetry relates scattering and annihilation processes to each other. Its derivation is straightforward in perturbative approaches to quantum field theory: it merely reflects the exchange of in- and outgoing states in Feynman diagram computations. In soliton models, the situation is much more complicated because the scattering and the annihilation processes concern distinct topological sectors that are not related by any continuous transformation. In this thesis a simple soliton model will be employed to address this problem numerically. First, in the unit topological sector we extract asymptotically the phase shift of the scattering process of a wave packet off the kink-solution. To this end we solve the time-dependent equation of motion of the non-integrable '4 field model in (1+1) spacetime dimensions for two distinct initial conditions: the wave packet in a trivial vacuum background and in the background of the kink-solution. Second, in the topologically trivial sector we present numerical solutions of the kink– antikink interaction in the same model. We find that the final state of this interaction varies dramatically with the impact velocity. As result, we analyze our numerical solutions for the kink–antikink collisions system in two regimes. For the initial velocity of the system less than some critical velocity, vc 0:26, the kink and the antikink either annihilate or inelastically scatter. On the other hand, the kink and the antikink always inelastically scatter when the initial velocity of the system is higher than this critical velocity. However, the scattering processes of the kink–antikink with initial velocity below and above the critical velocity are different. Below the critical velocity the kink and the antikink collide and always undergo n-bounces (n 2) before they depart to infinity. When the initial velocity of the system is higher than vc, the kink and the antikink depart to infinity after only one bounce. We present a qualitative description for these bounce effects between the kink and the antikink motivated by earlier studies as well as our numerical simulations. We utilize collective coordinates to study the dynamics of the kink–antikink system in two degrees of freedom. In this regime, we modify the ansätze of the kink–antikink system from earlier studies to account for relativistic effects. We perform a comparison between this approximation and the full system. We end our discussion of this sector by discussing the scattering data for the inelastic scattering and the annihilation processes of the kink–antikink. Third, we compare the extracted scattering data for the scattering process of a wave packet off the kink-solution and the annihilation process of the kink–antikink to each other. Finally, these studies of different sectors allow us to make a conjecture about the validity of crossing symmetry within the non-integrable '4 field model.
AFRIKAANSE OPSOMMING: Kruising-simmetrie beskryf ’n verband tussen verstrooiings- en vernietigingsprosesse. Die afleiding daarvan binne die raamwerk van steuringsteorie is eenvoudig: dit behels bloot die omruil van ingaande en uitgaande toestande in die Feynman-diagram. In soliton-modelle is die situasie egter meer ingewikkeld aangesien die verstrooiings- en vernietigingsprosesse in verskillende topologiese sektore plaasvind wat nie deur kontinue transformasies aan mekaar gekoppel is nie. In hierdie tesis word daar van ’n eenvoudige soliton-model gebruik gemaak om hierdie probleem numeries te ondersoek. Eerstens word die faseverskuiwing van die verstrooiingsproses van ’n golfpakkie vanaf ’n kinkoplossing asimptoties in die topologiese eenheidssektor bepaal. Vir hierdie doel word die tydafhanklike bewegingsvergelykings van die klassieke, nie-integreerbare 4-veldeteorie in (1+1) dimensionele ruimte-tyd opgelos. Twee beginkondisies word ondersoek: ’n golfpakkie in die triviale vakuum agtergrond asook in die kinkoplossing agtergrond. Tweedens ondersoek ons ook numeriese oplossings vir die kink-antikink wisselwerking binne die triviale topologiese sektor van dieselfde model. Hier vind ons dat die finale toestand van hierdie wisselwerkingsproses op ’n uiters sensitiewe wyse van die impaksnelheid afhang. Ons ondersoek gevolglik die numeriese oplossings vir die kink-antikink botsings in twee gebiede. Vir beginsnelhede onder die kritieke snelheid vc 0:26 sal die kink en antikink mekaar óf vernietig óf nie-elasties verstrooi. In teenstelling hiermee sal die kink-antikink altyd nie-elastiese verstrooiing ondergaan as die beginsnelheid die kritieke snelheid oorskry. Die aard van die verstrooiingsprosesse vir beginsnelhede bo en onder die kritieke snelheid is egter verskillend. Onder die kritieke snelheid sal die kink en antikink ’n n-bots proses (n 2) ondergaan voor hulle finaal van mekaar weg beweeg. Bo die kritieke snelheid sal die kink-antikink egter net ’n enkele botsing ondergaan en dan uitmekaar beweeg. Ons lewer ’n kwalitatiewe beskrywing vir die bons-effek tussen die kink en antikink wat deur vorige studies asook ons numeriese resultate gemotiveer word. Ons maak gebruik van ’n kollektiewe koördinaatstelsel om die dinamika van die kink-antikink in terme van twee vryheidsgrade te bestudeer. In hierdie gebied pas ons ook die ansatz vir die kink-antikink stelsel aan om relatiwistiese effekte in ag te neem. Ons vergelyk dan hierdie benadering met die oplossing van die volle sisteem. Die bespreking van hierdie sektor word afgesluit met ’n analise van die verstrooiingsdata vir die verstrooiing- en vernietingsprosesse van die kink-antikink. Derdens vergelyk ons die verstrooiingsdata vir die verstrooiing van ’n golfpakkie vanaf ’n kinkoplossing met die van die vernietigingsproses van die kink-antikink. Ons studie van die verskillende sektore laat ons dan toe om ’n vermoede te formuleer oor die geldigheid van kruissing-simmetrie binne die nie-integreerbare 4-model.
13
Adams, N. « Symmetry restoration near a black hole ». Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372638.
14
Lawrence, Mark. « Symmetry and topology at the metasurface ». Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6152/.
Résumé :
Since the metamaterials ethos of geometry over chemistry was first conceived at the end of the last century, a great deal of effort has been directed towards the conceptual, computational and experimental development of myriad effective electromagnetic media. Taking inspiration from quantum mechanics, here we exploit the possibility of independently controlling the individual elements of an effective polarizability matrix to reveal unique polarisation based phenomena. Firstly, by employing resonant “meta-atoms” to selectively absorb specific polarisation states of THz radiation, while tuning the polarisation conversion efficiency via near-field coupling, Parity Time symmetry breaking has been proposed, based on analytical and numerical modelling, and observed, using THz-Time Domain Spectroscopy, in polarisation space for the first time. We also reveal that anisotropic material as well radiative loss can be highly useful for tailoring the response of resonant metamaterials. Secondly, the possibility of achieving a topologically non-trivial phase within an effectively homogeneous photonic medium is discussed. Originating from the inherent spin-orbit interaction for light, three dimensional metamaterials with chirality and hyperbolicity are shown to be topologically non-trivial, resulting in one-way surface waves that are immune to back-scattering. Building on the effective medium calculations, our predictions are confirmed by numerical studies of realistic meta-structures.
15
Narasimhan, Subha. « The energetics and symmetry of quasicrystals / ». The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487585645576348.
16
Ramlakan, Alastair. « Flavour SU(3) symmetry breaking in quantum chromodynamics ». Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/6547.
Résumé :
Includes bibliographical references.The subject of this thesis is the determination of the size of SU(3) flavour symmetry breaking in the QeD vacuum, as measured by the ratio of the strange to non-strange quark vacuum condensates
17
Baskerville, W. K. « Braided groups, symmetry and the skyrme crystal ». Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364387.
18
Gear, James Manning. « PT symmetry and exceptional points in metamaterials ». Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7876/.
Résumé :
Parity-Time (PT) symmetry has recently received much attention as a promising alternative to the condition of Hermiticity. PT symmetric systems have two distinct phases where behaviour is split between Hermitian evolution where it has real eigenvalues and non-Hermitian evolution where it has complex eigenvalues. At the crossover between these two phases, there is an exceptional point: a special kind of eigenvalue degeneracy unique to non-Hermitian system which can result in interesting properties. In this thesis, we will first review the field of metamaterials and show how they can be used to design electromagnetic potentials. We will also review the current understanding of PT symmetry and its associated effects in electromagnetism. We will then develop a new form of parity operator which can be used in conjunction with the time-reversal operator to derive new conditions on the constitutive matrix. This parity operator will then be used to understand the link between PT symmetry and exceptional points with experimental support from a metamaterial system. We will additionally look at some other applications of PT symmetry, specifically in the context of lasing and absorption, and attempt to design a structure which uses this symmetry.
19
Gebauer, Astrid. « Chiral symmetry breaking transitions in holographic duals ». Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/206257/.
Résumé :
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.
20
Krumins, Andris Visvaldis. « Symmetry, conservation laws, and theoretical particle physics, 1918-1979 ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0004/NQ41198.pdf.
21
Alsufyani, Nada. « The Iterative Method for Quantum Double-well and Symmetry-breaking Potentials ». DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2017. http://digitalcommons.auctr.edu/cauetds/62.
Résumé :
Numerical solutions of quantum mechanical problems have witnessed tremendous advances over the past years. In this thesis, we develop an iterative approach to problems of double-well potentials and their variants with parity-time-reversal symmetry- breaking perturbations. We show that the method provides an efficient scheme for obtaining accurate energies and wave functions. We discuss in this thesis potential applications to a variety of related topics such as phase transitions, symmetry breaking, and external field-induced effects.
22
Moerman, RobertWilliam. « A gauge-invariant, symmetry-preserving truncation of JIMWLK ». Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27998.
Résumé :
The colour glass condensate captures quantum chromodynamics in its application to high-energy collider experiments in the spirit of an effective field theory. In deeply inelastic lepton-hadron scattering experiments, as well as in hadron-hadron collisions, the internal degrees of freedom of in-state hadrons are dominated by a dense medium of gluonic matter called the colour glass condensate. Interactions with this medium by some (dilute) probe are most naturally described in terms of Wilson-lines and their correlators. The energy-dependence of these correlators is given by the JIMWLK (Jalilian-Marian+Iancu+McLerran+Weigert+Leonidov+Kovner) equa- tion which, when applied to a correlator, generates an infinite tower of coupled Dyson-Schwinger- like equations referred to as a Balitsky Hierarchy. In this thesis, I present a novel method for truncating, in a gauge-invariant and symmetry- preserving manner, the Balitsky hierarchy associated with matrices of Wilson-line correlators. This truncation is realized by parameterizing the energy-dependence of the symmetric and anti- symmetric parts of these matrices independently via energy-evolution operators which evolve ini- tial conditions in a manner akin to the time-evolution of Hermitian operators in the Heisenberg picture of quantum mechanics. These energy-evolution operators are path-ordered exponentials whose exponents are expanded in terms of energy-dependent "colour structure functions". I show how the properties of contributions to the expansion of these exponents (at each order in the expansion) are constrained by the group theory of SU(Nc).
23
Bergman, Oren. « Nonrelativistic conformal symmetry in 2+1 dimesional field theory ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32619.
24
Mantry, Gautam. « Heavy quark symmetry in the soft collinear effective theory ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32309.
Résumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (leaves 189-198).
We study strong interaction effects in nonleptonic decays of ... mesons with energetic particles in the final state. An introduction to Soft Collinear Effective Theory (SCET), the appropriate effective field theory of QCD for such decays, is given. We focus on decays of the type ... where M is a light energetic meson of energy E. The SCET formulates the problem as an expansion in powers of where Q [approx.] ... . A factorization theorem is proven at leading order that separates the physics of the scales ... . In addition, the factorization theorem decouples energetic degrees of freedom associated with the light meson allowing us to derive heavy quark symmetry relations between the ... type amplitudes. A new mechanism for the generation of non-perturbative strong phases is shown within the framework of factorization. Heavy quark symmetry relations are shown to apply for these strong phases as well. Furthermore, the strong phases for certain light mesons in the final state are shown to be universal. The analysis is extended to ... type decays with isosinglet light mesons and excited charmed mesons in the final state respectively. A host of other phenomenological relations are derived and found to be in good agreement with available data.
by Gautam Mantry.
Ph.D.
25
Wang, Juven Chun-Fan. « Aspects of symmetry, topology and anomalies in quantum matter ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99285.
Résumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 223-230).
To understand the new physics and richness of quantum many-body system phenomena is one of the stimuli driving the condensed matter community forward. Importantly, the new insights and solutions for condensed matter theory sometimes come from the developed and developing knowledge of high energy theory, mathematical and particle physics, which is also true the other way around: Condensed matter physics has been providing crucial hints and playgrounds for the fundamental laws of high energy physics. In this thesis, we explore the aspects of symmetry, topology and anomalies in quantum matter with entanglement from both condensed matter and high energy theory viewpoints. The focus of our research is on the gapped many-body quantum systems including symmetry-protected topological states (SPTs) and topologically ordered states (TOs). We first explore the ground state structures of SPTs and TOs: the former can be symmetry twisted and the latter has robust degeneracy. The Berry phases generated by transporting and overlapping ground state sectors potentially provide universal topological invariants that fully characterize the SPTs and TOs. This framework provides us the aspects of symmetry and topology. We establish a field theory representation of SPT invariants in any dimension to uncover group cohomology classification and beyond -- the former for SPTs with gapless boundary gauge anomalies, the latter for SPTs with mixed gauge-gravity anomalies. We study topological orders in 3+1 dimensions such as Dijkgraaf-Witten models, which support multi-string braiding statistics; the resulting patterns may be analyzed by the mathematical theory of knots and links. We explore the aspects of surface anomalies of bulk gapped states from the bulk-edge correspondence: The gauge anomalies of SPTs shed light on the construction of bosonic anomalies including Goldstone-Wilczek type, and also guide us to design a non-perturbative lattice model regularizing the low-energy chiral fermion/gauge theory towards the Standard Model while overcoming the Nielsen-Ninomiya fermion-doubling problem without relying on Ginsparg-Wilson fermions. We conclude by utilizing aspects of both quantum mechanical topology and spacetime topology to derive new formulas analogous to Verlinde's via geometric-topology surgery. This provides new insights for higher dimensional topological states of matter.
by Juven Chun-Fan Wang.
Ph. D.
26
Bone, Richard George Andrew. « New applications of the molecular symmetry group ». Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239761.
27
Dewar, Neil Archdale. « Symmetries in physics, metaphysics, and logic ». Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:38b380cb-7f64-40cb-b94c-eba4b3b652ac.
Résumé :
This thesis examines the idea that when a physical theory contains symmetries, the theory should be interpreted in such a way that symmetry-related models represent the same physical state of affairs. It argues that we can best do so by drawing on analogies to ideas in philosophy of logic and language: specifically, by thinking of symmetries as a means of translating a theory into itself. It consists of six chapters, together with an introduction and conclusion. In Chapter 1, I set up the main ideas needed to more precisely frame the question at hand: namely, the notions of symmetry, interpretation, and possibility. I make some remarks about how I take these to be connected. In Chapter 2, I argue that isomorphic models should be interpreted as equivalent. After giving some motivations for doing so, I consider the main obstruction: how to provide an account of de re modality. I review how counterpart theory may be used to overcome this obstruction, and clarify how counterpart theory relates to other positions in the debate over modality de re. In Chapter 3, I show that the metaphysical debate over quidditism can be made precise by drawing on notions of translation from model theory, and argue in favour of an anti-quidditist attitude towards interpreting theories. I then consider the special case of translating a theory into itself: how such a theory should be interpreted, and what reformulations of the theory such an interpretation suggests. In Chapter 4, I turn my attention to physics. I define the notion of an internal symmetry for a theory, and argue that they may be regarded as translations from a theory into itself (in the sense of Chapter 3); and, hence, that symmetry-related models should be interpreted as equivalent. Drawing on the analogy further, I look at how the theory may be reformulated to take this interpretation into account. In Chapter 5, I look at external symmetries. I argue, drawing on ideas from Chapters 2 and 3, that models related by external symmetries should also be interpreted as equivalent. I discuss how implementing this interpretational lesson bears on finding the spacetime structure appropriate to a theory. In Chapter 6, I consider a specific external symmetry: the accelerative symmetry of Newtonian gravitation. I show that one can reformulate the theory to take this into account, setting gravitation on a spacetime structure that has absolute rotation but no absolute acceleration.
28
Klein, Kreisler Martin. « Chiral symmetry restoration in finite temperature QEDâ†3 ». Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316877.
29
Ashworth, Richard Michael. « Quantum field theories having conformal and chiral symmetry ». Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292952.
30
Feudel, Fred, Norbert Seehafer, Barak Galanti et Sten Rüdiger. « Symmetry breaking bifurcations for the magnetohydrodynamic equations with helical forcing ». Universität Potsdam, 1996. http://opus.kobv.de/ubp/volltexte/2007/1431/.
Résumé :
We have studied the bifurcations in a three-dimensional incompressible magnetofluid with periodic boundary conditions and an external forcing of the Arnold-Beltrami-Childress (ABC) type. Bifurcation-analysis techniques have been applied to explore the qualitative behavior of solution branches. Due to the symmetry of the forcing, the equations are equivariant with respect to a group of transformations isomorphic to the octahedral group, and we have paid special attention to symmetry-breaking effects. As the Reynolds number is increased, the primary nonmagnetic steady state, the ABC flow, loses its stability to a periodic magnetic state, showing the appearance of a generic dynamo effect; the critical value of the Reynolds number for the instability of the ABC flow is decreased compared to the purely hydrodynamic case. The bifurcating magnetic branch in turn is subject to secondary, symmetry-breaking bifurcations. We have traced periodic and quasi- periodic branches until they end up in chaotic states. In particular detail we have analyzed the subgroup symmetries of the bifurcating periodic branches, which are closely related to the spatial structure of the magnetic field.
31
Bonnoit, Craig John. « Inelastic X-ray scattering studies of broken symmetry in BSCCO ». Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83827.
Résumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 165-178).
Interactions between charge and lattice degrees of freedom play a critical role in determining the properties of canonical BCS superconductors where integration out of the phonon subsystem results in an effective pairing interaction between electrons. In the study of high temperature superconductors the importance of phonons is less well understood and charge ordering properties vary between the families of high-Tc cuperates. While superconductivity in these materials is not believed to originate from phonon excitations, there is evidence for strong electron-phonon coupling from significant electron dispersion renormalization and the observation of increased breadth in optical Cu-O bond modulating phonons. Here we present measurements of acoustic phonons in single and double layer BSCCO which show several effects: broadening of the longitudinal acoustic in correspondence to approximately period-four ordering tendencies and signatures of time-reversal and inversion symmetry breaking. Measurement of these anomalous properties is feasible due to renormalization of the lattice propagator by strong interactions with underlying symmetry-breaking electronic states. These symmetries are broken at room temperature for all materials in the 'strange metal' state above the pseudogap, but are enhanced, particularly around the period four intercell ordering wavevector, as the system is cooled into the pseudogap state. In-plane acoustic phonons are a probe of the electron physics localized on the Cu-O plane due to the residual eigenvector components in this plane. These phonon measurements then present a picture of BSCCO in which charge correlations stay dynamic with a pronounced tendency toward ordering at a specific wave-vector and an underlying symmetry-breaking ground state.
by Craig John Bonnoit.
Ph.D.
32
arapKoske, Samuel Kiprono. « Effects of symmetry lowering in metal cluster complexes ». Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291550.
33
Jansson, Henrik. « Unification in Particle Physics ». Thesis, Uppsala universitet, Högenergifysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295813.
Résumé :
During the twentieth century, particle physics developed into a cornerstone of modern physics, culminating in the Standard Model. Even though this theory has proved to be of extraordinary power, it is still incomplete in several respects. It is our aim in this bachelor thesis to discuss some possible theories beyond the Standard Model, the main focus being on Grand Unified Theories, while also taking a look at attempts of further unication via discrete family symmetry. At the heart of all these theories lies the concept of local gauge invariance, which is introduced as a fundamental principle, followed by an overview of the Standard Model itself. No theory has so far managed to unify all elementary particles and their interactions, but some interesting features are highlighted. We also give a hint at some possible paths to go in the future in the quest for a unication in particle physics.Under 1900-talet utvecklades partikelfysiken till en av de fundamentala teorierna inom fysiken, och kom att sammanfattas i den s.k. Standardmodellen. Även om denna modell rönt exceptionella framgånger vad gäller beskrivningen av elementarpartiklar och deras växelverkan, är den fortfarande ofullständig på flera sätt. Syftet med denna kandidatuppsats är att diskutera möjliga teorier bortom Standardmodellen såsom Storförenande Teorier och diskreta familjesymmetrier vars avsikt är att koppla samman de tre familjerna av fermioner i Standardmodellen. Men först introduceras idén om lokal gaugeinvarians, vilken ligger till grund for dessa teorier, varpå en översikt av Standardmodellen följer. Ingen teori har ännu lyckats ge en helt tillfredsställande bild av elementarpartiklar och deras interaktion, men en del intressanta egenskaper hos föreslagna teorier belyses i denna uppsats. Slutligen ges en del spekulativa förslag på väger att gå i framtida försök till föreningar inom partikelfysiken.
34
Kröger, Jens 1981. « Elastic behavior and freezing of crystals with square symmetry ». Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84048.
Résumé :
The main purpose of this thesis is to justify the density functional theory of freezing in the case of a crystal with square symmetry. In the first part, I discuss the widely used technique of molecular dynamics to characterise the dynamics and statistical observables of a system undergoing a phase transition. I then outline the advantages and the main drawbacks of this technique: slow implementation and poor performance for long time scales. It is shown that order parameter or phenomenological theories of freezing paliate those problems. These theories describe the dynamics of one parameter that starts in a highly symmetric state and which symmetry is broken during the phase transition. The dynamics of the order parameter, which in our case is the time averaged density, is governed by the topology of a free energy functional. We derive such a free energy functional for two theories and explain why one of these can be applied to give freezing into arbitrary symmetry groups. The study of freezing into square symmetry and various elastic deformations of two-dimensional crystals form the last part of the thesis.
35
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.
36
Mellars, Ehren Axel. « Time-reversal symmetry and topology in one-dimensional Josephson junctions ». Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8739/.
Résumé :
We explore the roles of topology and time-reversal symmetry in one-dimensional superconducting systems. Specifically, we examine junctions involving time-reversal-invariant topological superconductors, which are characterised by the emergence of zero-energy Majorana- Kramers pairs at their boundaries. For Josephson junctions composed of these superconductors, we obtain, through a scattering matrix technique valid in a regime where the junction length is much shorter than the superconducting coherence length, exact analytical and numerical results for the Josephson current in terms of a small number of independently measurable junction parameters. The current is found to have a number of prominent and robust features which indicate the underlying symmetries and the nontrivial topology inherent in these systems. The most remarkable of these features occurs in the form of switches in the Josephson current, where the sign of the current reverses as a consequence of crossings between energy levels in the subgap spectrum. By utilising a quantum master equation approach, we establish general conditions under which these switches manifest in relation to a phenomenological relaxation rate and a voltage applied across the junction. Our findings enable quantitative predictions for such junctions, potentially assisting in experimental directions regarding the detection of Majorana- Kramers pairs in mesoscopic Josephson systems.
37
Sigrist, Norbert. « First-order design of mirror systems with no axial symmetry ». Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284660.
Résumé :
All-reflective imaging systems that are asymmetrical and eccentric have the advantage of providing more degrees of freedom to improve image quality. A disadvantage of these asymmetrical imaging systems is that they suffer from asymmetric mapping. This asymmetric mapping manifests itself mainly in the presence of keystone distortion and anamorphism. Due to the increase in degrees of freedom, the complexity of such systems escalates; thus, the designer is confronted with the difficult task of determining optimal starting points. This work addresses several first-order aspects of the design and characterisation of asymmetrical, all-reflective, aspherical, eccentric imaging systems. In contrast to the work of Stone and Forbes, which is based upon the theory of Hamiltonian optics and includes both the first- and second-order considerations, this work is based upon the theory of collineation. Because of the inherent simplicity of the collinear mapping, which is a projective transformation, we are able to present a simple but certainly not naive way of designing and characterising such asymmetrical all-reflective imaging systems. The simplicity of this proposition has the advantage that we can gain insights into asymmetrical mapping behaviour. Specifically, we apply the collinear mapping model on all-reflective asymmetrical imaging systems resulting in the description of how the mapping between conjugate planes may be described. First we will define keystone distortion and anamorphism. Then we will introduce and investigate the significance of the Cardinal points and planes, the Scheimpflug condition and the horizon planes and show how they are applied in the designing of imaging systems that are free of both keystone distortion and anamorphism. Having established a first-order layout of the optical system, we will then develop a process for converting the first-order layouts into imaging systems consisting of real aspheric surfaces.
38
Moore, Joel Ellis 1973. « Phase transitions and symmetry breaking in disordered quantum Hall edge states ». Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8281.
Résumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.Includes bibliographical references (p. 94-96).
Tunneling into the edge of a quantum Hall droplet is a sensitive probe of the topological orders believed to exist in fractional quantum Hall states. The tunneling behavior of a general hierarchy state is studied within the chiral-Luttinger-liquid model of low-energy edge dynamics. Adding random hopping of quasiparticles between edge modes results in "symmetry restoration by disorder" and universal weak tunneling behavior in edges with modes traveling in both directions. We develop a boost coordinate technique and apply it to find the edge phases and tunneling exponents of all topologically stable principal hierarchy states. States with neutral modes in both directions along the edge have multiple stable fixed points which can be classified by their symmetries. When the tunneling current into an edge is large, the system can cross over from the weak-tunneling fixed point to a different strongly coupled fixed point with different conductance and effective charge. Edges with multiple modes can have multiple strongly coupled fixed points. We develop a general formalism to analyze weakly and strongly coupled fixed points of point tunneling. Adding interactions to tunneling between two Laughlin edges is shown to lead to a continuous variation of effective quasiparticle charge and conductance with interaction strength.
by Joel Ellis Moore.
Ph.D.
39
Bertolini, Daniele Ph D. Massachusetts Institute of Technology. « Electroweak symmetry breaking in the era of the Higgs boson discovery ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91079.
Résumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.166
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 115-125).
In this thesis we study possible deviations from the electroweak symmetry breaking mechanism as predicted by the Standard Model (SM), and we introduce a new framework to analyze hadronic final states at colliders. In the first part, we begin by considering supersymmetric extensions of the SM and by studying the connection between electroweak symmetry breaking and supersymmetry breaking. Contrary to the common lore, we show that a visible dynamics in the Higgs sector can contribute to supersymmetry breaking, as long as soft masses receive contributions also from one or more hidden sectors. A striking feature is the presence of a light pseudo-goldstino in the spectrum. We study potential collider signatures of visible supersymmetry breaking in Higgs and neutralino decays. Then, we move to a study of the Higgs data collected at the Large Hadron Collider (LHC). By using both measurements of the Higgs boson couplings, and limits on Higgs-like states at higher masses, we investigate whether the data support the possibility that the SM Higgs is mixed with another scalar. We consider fits to simplified models and we find that mixing angles with sin 2 6 > 0.2 are disfavored at 95% CL over a scalar mass range 200 - 1000 GeV. In the second part, we propose a new way to define inclusive jet (and subject) based observables at colliders. We introduce a new class of event shapes that characterize the jet-like structure of the event by using only information in the neighborhood of each particle. We show that conventional jet-based observables such as jet multiplicity, summed scalar transverse momentum, and missing transverse momentum can be recovered within this approach. We show that in this framework trimming can be recast as a particle weight assignment, without explicit jet identification. Finally, we comment on potential applications of the method both at trigger and analysis level.
by Daniele Bertolini.
Ph. D.
40
Pyykkönen, A. (Ari). « Parity symmetry-breaking phase transition in a nonlinear Rabi-Hubbard lattice ». Master's thesis, University of Oulu, 2015. http://urn.fi/URN:NBN:fi:oulu-201512082290.
Résumé :
Lattices consisting of cavity QED and circuit QED elements have come under focus as a platform for studying several novel quantum phenomena. In particular, a lattice of Rabi systems described by the Rabi-Hubbard model is expected to display a new Z2 parity symmetry-breaking phase transition of light between a Rabi insulator and a delocalized superradiant phase. In this thesis, we examine a superconducting circuit called the artificial trapped ion as a means to realize a nonlinear Rabi-Hubbard lattice. We use mean field theory and second-order perturbation theory to derive an expression for the boundary of the phase transition and calculate it numerically. We show that nonlinearity in the light-matter coupling results in nontrivial behavior for the phase boundary, in the form of a peak arising at a certain strength of the nonlinearity. We also see a behavior of oscillation followed by saturation as the nonlinearity increases.
41
Ogasahara, Atsushi. « Discrete flavor symmetry for lepton mixing and quark mixing ». 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/189340.
42
Hutzel, William D. « Particle-Hole Symmetry Breaking in the Fractional Quantum Hall Effect at nu = 5/2 ». Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10841528.
Résumé :
The fractional quantum Hall effect (FQHE) in the half-filled second Landau level (filling factor ν = 5/2) offers new insights into the physics of exotic emergent quasi-particles. The FQHE is due to the collective interactions of electrons confined to two-dimensions, cooled to sub-Kelvin temperatures, and subjected to a strong perpendicular magnetic field. Under these conditions a quantum liquid forms displaying quantized plateaus in the Hall resistance and chiral edge flow. The leading candidate description for the FQHE at 5/2 is provided by the Moore-Read Pfaffian state which supports non-Abelian anyonic low-energy excitations with potential applications in fault-tolerant quantum computation schemes. The Moore-Read Pfaffian is the exact zero-energy ground state of a particular three-body Hamiltonian and explicitly breaks particle-hole symmetry. In this thesis we investigate the role of two and three body interaction terms in the Hamiltonian and the role of particle hole symmetry (PHS) breaking at ν = 5/2. We start with a PHS two body Hamiltonian (H 2) that produces an exact ground state that is nearly identical with the Moore-Read Pfaffian and construct a Hamiltonian H(α) = (1 – α)H3 + α H 2 that tunes continuously between H3 and H2. We find that the ground states, and low-energy excitations, of H2 and H3 are in one-to-one correspondence and remain adiabatically connected indicating they are part of the same universality class and describe the same physics in the thermodynamic limit. In addition, evidently three body PHS breaking interactions are not a crucial ingredient to realize the FQHE at 5/2 and the non-Abelian quasiparticle excitations.
43
Elliott, Terry. « The top quark and electroweak symmetry breaking ». Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240631.
44
Cacciapaglia, Giacomo. « Models of electroweak symmetry breaking in extra dimensions ». Doctoral thesis, Scuola Normale Superiore, 2007. http://hdl.handle.net/11384/85850.
45
Mavimbela, Gcina A. « Time Reparametrization Symmetry and Spatial-Temporal Fluctuations in Glasses ». Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1354211400.
46
Bott, Christopher James. « Mirror Symmetry for K3 Surfaces with Non-symplectic Automorphism ». BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7456.
Résumé :
Mirror symmetry is the phenomenon, originally discovered by physicists, that Calabi-Yau manifolds come in dual pairs, with each member of the pair producing the same physics. Mathematicians studying enumerative geometry became interested in mirror symmetry around 1990, and since then, mirror symmetry has become a major research topic in pure mathematics. One important problem in mirror symmetry is that there may be several ways to construct a mirror dual for a Calabi-Yau manifold. Hence it is a natural question to ask: when two different mirror symmetry constructions apply, do they agree?We specifically consider two mirror symmetry constructions for K3 surfaces known as BHK and LPK3 mirror symmetry. BHK mirror symmetry was inspired by the LandauGinzburg/Calabi-Yau correspondence, while LPK3 mirror symmetry is more classical. In particular, for algebraic K3 surfaces with a purely non-symplectic automorphism of order n, we ask if these two constructions agree. Results of Artebani Boissi`ere-Sarti originally showed that they agree when n = 2, and more recently Comparin-Lyon-Priddis-Suggs showed that they agree when n is prime. However, the n being composite case required more sophisticated methods. Whenever n is not divisible by four (or n = 16), this problem was solved by Comparin and Priddis by studying the associated lattice theory more carefully. In this thesis, we complete the remaining case of the problem when n is divisible by four by finding new isomorphisms and deformations of the K3 surfaces in question, develop new computational methods, and use these results to complete the investigation, thereby showing that the BHK and LPK3 mirror symmetry constructions also agree when n is composite.
47
Cullerne, John Paul. « The Jahn-Teller effect in icosahedral symmetry ». Thesis, University of Oxford, 1995. http://ora.ox.ac.uk/objects/uuid:cc2b3605-f7dc-488d-820d-3a830a0119b3.
Résumé :
The resurgence of interest in properties of molecules of icosahedral symmetry follows the discovery of the C60 molecule. Due to the high symmetry of the icosahedron, almost all the electronic and vibrational levels are highly degenerate, so that in dealing with properties of these systems, the Jahn-Teller interaction must almost always be allowed for. This thesis primarily explores the properties of the icosahedral G ⊗ (g ⊕ h] interaction and related subsystems in the strong coupling régime. Mappings of the adiabatic potential energy surfaces facilitate an analysis of the geometrical phase or Berry phase acquired by the quantal system on transportation around adiabatic circuits in parameter space. The Berry phase information in conjunction with an analysis of tunnelling, determines the properties of the ground state. The use of Ham factors achieves a characterization of the various coupling régimes. However, characterization of G and H Jahn-Teller systems, requires an extension of the standard definition of these Ham factors. In such cases the extended matrix elements between and within vibronic tunnelling sublevels cannot be ignored. A calculation of all the standard and extended matrix elements is presented. A further introduction of a matrix of Ham factors facilitates the description of H multiplicity within an H manifold. Finally, two problems are investigated numerically; aimed at making some allusion towards possible experimental manifestations of G ⊗(g(⊕)h). The first investigation considers the variations in the eigensystem and Ham factors of G ⊗ (g ⊕ h), as a function of the coupling to the two modes. The second investigation considers the structure in the optical absorption line shapes for the transitions from orbital singlet to quartet, G, states in an icosahedral environment. The quartet states are subject to both spin-orbit and linear Jahn-Teller interactions.
48
Athron, Peter. « Aspects of electroweak symmetry breaking in physics beyond the standard model ». Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/513/.
Résumé :
Fine tuning in the Standard Model (SM) is the basis for a widespread expectation that the minimal model for electroweak symmetry breaking, with a single Higgs boson, is not realised in nature and that new physics, in addition to (or instead of) the Higgs, will be discovered at the Large Hadron Collider (LHC). However constraints on new physics indicate that many models which go beyond the SM (BSM) may also be fine tuned (although to a much lesser extent). To test this a reliable, quantitative measure of tuning is required. We review the measures of tuning used in the literature and propose an alternative measure. We apply this measure to several toy models and a constrained version of the Minimal Supersymmetric Standard Model. The Exceptional Supersymmetric Standard Model (E6SSM) is another BSM motivated by naturalness. As a supersymmetric theory it solves the SM hierarchy problem and by breaking a new gauged U(1) symmetry it also solves the μ-problem of the MSSM. We investigate the Renormalisation Group Evolution of the model and test for radiative electroweak symmetry breaking in two versions of the model with different high scale constraints. First we briefly look at scenarios with non-universal Higgs masses at the GUT scale and present a particle spectrum that could be observed at the LHC. Secondly we study the constrained E6SSM (CE6SSM), with universal scalar (m0), trilinear (A0) and gaugino (M) masses. We reveal a large volume of CE6SSM parameter space where the correct breakdown of the gauge symmetry can be achieved and all experimental constraints can be satisfied. We present benchmark points corresponding to different patterns of the particle spectrum. A general feature of the benchmark spectra is a light sector of SUSY particles consisting of a light gluino, two light neutralinos and a light chargino. Although the squarks, sleptons and Z′ boson are typically much heavier, the exotic color triplet charge 1/3 fermions as well as the lightest stop can be also relatively light leading to spectacular new physics signals at the LHC.
49
Morin, Bertrand. « Symmetry and superconformal structures of the heterotic string ». Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61915.
50
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.
Résumé :
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.