Yung Lit Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves p. [122]-124). / Text in English; abstracts in English and Chinese. / Yung Lit Hung. / Abstract --- p.i / Acknowledgements --- p.ii / List of Figures --- p.v / List of Tables --- p.vii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Dissipative two-state system --- p.3 / Chapter 2.1 --- Introduction --- p.3 / Chapter 2.2 --- A two-state system viewed as a spin --- p.4 / Chapter 2.3 --- Rotation of spin operators --- p.5 / Chapter 2.4 --- Dissipative two state system --- p.7 / Chapter 2.5 --- The model in consideration --- p.8 / Chapter 2.5.1 --- gk= 0 --- p.8 / Chapter 2.5.2 --- Δ0 = 0 --- p.8 / Chapter 2.5.3 --- dispersionless phonon case with constant coupling --- p.10 / Chapter 3 --- Linearized spin-wave approximation and mean-field method --- p.13 / Chapter 3.1 --- Holstein Primakoff Transformation --- p.13 / Chapter 3.2 --- Application of linearized spin-wave approxmation to our system --- p.14 / Chapter 3.3 --- Mean-field method --- p.24 / Chapter 4 --- Variational method for optical phonons with constant coupling --- p.35 / Chapter 4.1 --- Introduction --- p.35 / Chapter 4.2 --- Variational Principle --- p.35 / Chapter 4.3 --- Variational Principle applied to optical phonon case --- p.36 / Chapter 4.4 --- Results --- p.41 / Chapter 4.5 --- Conclusion --- p.54 / Chapter 5 --- Variational method for acoustic phonons with ohmic dissipation --- p.56 / Chapter 5.1 --- Introduction --- p.56 / Chapter 5.2 --- Variational Principle applied to acoustic phonon case --- p.57 / Chapter 5.3 --- μk= 0 case --- p.59 / Chapter 5.4 --- Search for any μk≠ 0 solution --- p.60 / Chapter 5.5 --- Results --- p.62 / Chapter 5.6 --- Conclusion --- p.70 / Chapter 6 --- Coupled Cluster Method --- p.72 / Chapter 6.1 --- Introduction --- p.72 / Chapter 6.2 --- Coupled Cluster Method --- p.73 / Chapter 6.2.1 --- Zeroth Level --- p.74 / Chapter 6.2.2 --- First Level --- p.74 / Chapter 6.2.3 --- The bra-state --- p.75 / Chapter 6.3 --- Coupled cluster method applied to our system --- p.76 / Chapter 6.4 --- Coupled cluster method applied to optical phonon case --- p.78 / Chapter 6.4.1 --- First Level --- p.79 / Chapter 6.4.2 --- Second Level --- p.81 / Chapter 6.5 --- Coupled cluster method applied to acoustic phonon case --- p.90 / Chapter 6.5.1 --- First Level --- p.90 / Chapter 6.5.2 --- Second Level --- p.92 / Chapter 6.6 --- Conclusion --- p.98 / Chapter 7 --- Spin system interacting with a photon field --- p.99 / Chapter 7.1 --- Rotation wave approximation --- p.100 / Chapter 7.2 --- Spin system interacting with an optical field --- p.101 / Chapter 7.3 --- Heisenberg equation of motion --- p.102 / Chapter 7.4 --- Brogoliubov transformation approach --- p.104 / Chapter 7.5 --- Conclusion --- p.106 / Chapter A --- Supplementary calculations --- p.107 / Chapter A.1 --- First level calculation for optical photon --- p.107 / Chapter A.2 --- Second level calculation for optical photon --- p.111 / Chapter A.3 --- First level calculation for acoustic photon --- p.114 / Chapter A.4 --- Second level calculation for acoustic photon --- p.118 / Bibliography --- p.121

A study is presented on the production of vector boson (W and Z0) events in association with recoiling hadronic activity in the form of hadronic jets, using proton-proton collisions at the LHC. The dataset was taken by the ATLAS detector during the 2011 data-taking run, at a centre of mass energy p s = 7 TeV, and corresponds to an integrated luminosity of 4.6 fb 1. A measurement of the cross-section ratio of W+jets Z+jets events is de ned, reducing the large systematic uncertainties inherent in the experimental measurement of such events. Inclusive and di erential cross-sections are presented for W+jets Z+jets , as a function of a range of kinematic variables, and are compared to state-of- the-art theoretical predictions.

We apply a diagrammatic approach to study Higgs boson, a color-neutral heavy particle, production in nucleus-nucleus collisions in the saturation framework without quantum evolution. We assume the strong coupling constant much smaller than one. Due to the heavy mass and colorless nature of Higgs particle, final state interactions are absent in our calculation. In order to treat the two nuclei dynamically symmetric, we use the Coulomb gauge which gives the appropriate light cone gauge for each nucleus. To further eliminate initial state interactions we choose specific prescriptions in the light cone propagators. We start the calculation from only two nucleons in each nucleus and then demonstrate how to generalize the calculation to higher orders diagrammatically. We simplify the diagrams by the Slavnov-Taylor-Ward identities. The resulting cross section is factorized into a product of two Weizsäcker-Williams gluon distributions of the two nuclei when the transverse momentum of the produced scalar particle is around the saturation momentum. To our knowledge this is the first process where an exact analytic formula has been formed for a physical process, involving momenta on the order of the saturation momentum, in nucleus-nucleus collisions in the quasi-classical approximation. Since we have performed the calculation in an unconventional gauge choice, we further confirm our results in Feynman gauge where the Weizsäcker-Williams gluon distribution is interpreted as a transverse momentum broadening of a hard gluons traversing a nuclear medium. The transverse momentum factorization manifests itself in light cone gauge but not so clearly in Feynman gauge. In saturation physics there are two different unintegrated gluon distributions usually encountered in the literature: the Weizsäcker-Williams gluon distribution and the dipole gluon distribution. The first gluon distribution is constructed by solving classical Yang-Mills equation of motion in the McLerran-Venugopalan model, while the second gluon distribution is related to the dipole scattering amplitude. So far, the quantum structure of the dipole gluon distribution has not been thoroughly investigated. Applying the same diagrammatic techniques, we carry out a detail study of the quantum structure of the color dipole gluon distribution, and then compare it with that of the Weizsäcker-Williams gluon distribution.

No description available.

Neste trabalho estudamos as propriedades termodinâmicas da Condensação de Bose-Einstein (CBE) para um gás de bósons não-interagentes confinado em potenciais bidimensionais V(x,y) que apresentam classicamente, um caos-suave (soft chaos), isto é, um espaço de fases compartilhado por ilhas de estabilidade e mares de caos. O formalismo estatístico mais apropriado para os nossos objetivos é o descrito pelo ensemble canônico, de forma que o número de partículas N é mantido fixo em cada simulação. Nosso principal objetivo é investigar se o caos pode caracterizar algum comportamento distinto nas propriedades do Condensado de Bose-Einstein. Para comparação dos nossos resultados com a literatura, mostramos em detalhes todos os cálculos para o oscilador bidimensional e a caixa bidimensional suavizados1. No potencial harmônico a suavização implica em um amortecimento da freqüência de oscilação, enquanto que para a caixa bidimensional, a suavização implica em um aumento da área da caixa quando N é aumentado. Esse recurso é necessário, uma vez que não se define rigorosamente uma transição de fase em sistemas com dimensão menor que três. Embora a suavização pareça ser mais um recurso matemático que físico, ela descreve bem a CBE em potenciais suaves. Para estudar o efeito do caos na CBE, escolhemos dois potenciais: i) O potencial Nelson, que é um potencial parabólico que descreve essencialmente dois osciladores harmônicos x e y com um termo de acoplamento não-linear que origina caos; ii) O potencial quártico, cuja base é mais achatada parecendo-se mais com uma caixa. Simulamos também a situação em que a partícula confinada é sujeita a um campo magnético perpendicular uniforme ao longo do eixoz. Os nossos resultados mostram que estatísticas que são bilineares em relação à densidade de energia do potencial de confinamento, como a variância do número de ocupação do estado fundamental, exibem assinatura do caos subjacente. / In this work we examine some of the thermodynamics propertie of Bose-Einstein Condensation (BEC) for a gas of non-interacting bosons trapped in bidimensional potentials V(x,y). We choose potentials that exhibits soft chaos in the classical regime which means they have a mixed phase space where islands of stability share the space with chaotic seas. We also describe the statistics via the canonical ensemble formalism which is more appropriate for our purposes. In this case, the number of particles N is kept fixed through each numerical simulation. Our main goal is to detect, if there is any, influence of the subjacent chaotic behavior in the BEC. For a matter of comparison, we show in details the calculations of both smoothed bidimensional harmonic oscillator and smoothed bidimensional box. The smoothing is equivalent to weakening the potential, so that it can be understood as to slowing down the oscillator frequency and to an enlargement of the box side as N is increased. This is necessary since phase transitions are rigorously violated in systems with dimension d < 3. Although this smoothing seems rather artificial, it models well BEC in non-rigid potentials. In order to study any possible fingerprint of chaos in the Bose-Einstein condensate we choose two potentials: i) Nelson Potential which is a paraboloid describing two harmonic oscillators coupled via a term that is responsible for the chaos in the system and ii) Quartic Potential which has a flat bottom resembling a box. We were also able to simulate the potentials with uniform magnetic field in the z direction. Our results show that statistics that are bilinear in the potential density of states like the particle number fluctuation of the ground state exhibit some fingerprints of the subjacent chaos.

Lu, Wenlong = 一维光格子中费米型原子混合物基态行为的玻色化研究 / 魯文龙. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (p. 70-72). / Abstract also in Chinese. / Lu, Wenlong = Yi wei guang ge zi zhong Feimi xing yuan zi hun he wu ji tai xing wei de Bose hua yan jiu / Lu Wenlong. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Cold-atom systems --- p.1 / Chapter 1.1.1 --- Optical lattices --- p.2 / Chapter 1.1.2 --- Feshbach resonance --- p.3 / Chapter 1.2 --- Outline of the thesis --- p.6 / Chapter 2 --- Bosonization method --- p.8 / Chapter 2.1 --- Special property of one-dimensional Fermion system --- p.9 / Chapter 2.2 --- Bosonization techniques --- p.13 / Chapter 2.2.1 --- Density operators as bosonic fields --- p.14 / Chapter 2.2.2 --- Bosonization Identities --- p.17 / Chapter 2.3 --- Renormalization analysis for Sine-Gordon field --- p.19 / Chapter 2.4 --- Summary --- p.25 / Chapter 3 --- Mass imbalance in the spin polarized fermion system --- p.26 / Chapter 3.1 --- Kinetic term --- p.29 / Chapter 3.2 --- Interaction term --- p.32 / Chapter 3.3 --- Phase separation --- p.38 / Chapter 3.4 --- Dominant order and pairing behavior --- p.47 / Chapter 3.5 --- Summary --- p.49 / Chapter 4 --- Mass imbalance in the strong repulsive interaction region --- p.50 / Chapter 4.1 --- Effective Hamiltonian at large U limit --- p.50 / Chapter 4.2 --- Bosonization of t-J-Jz model --- p.54 / Chapter 4.3 --- Phase separation --- p.60 / Chapter 4.4 --- Summary --- p.67 / Chapter 5 --- Conclusions --- p.68 / Bibliography --- p.70 / Chapter A --- Proofs of Bosonization --- p.73 / Chapter A.1 --- Anti-commutation relations between two branches of fermionic field operators --- p.73 / Chapter A.2 --- Bosonization-identities checking --- p.74 / Chapter B --- Diagonalization of Quadratic Hamiltonian with Two Bosonic Fields --- p.77 / Chapter C --- Correlation functions --- p.82

Few and many-body systems usually feature interesting and novel behaviors compared with their counterparts in three dimensions. On one hand, low dimensional physics presents challenges due to strong interactions and divergences in the perturbation theory; On the other hand, there exist powerful theoretical tools such as the renormalization group and the Bethe ansatz. In this thesis, I discuss two examples: three interacting bosons in two dimensions and interacting bosons/fermions in one dimension. In both examples, there are intraspecies repulsion as well as interspecies attraction, producing a rich spectrum of phenomena. In the former example, a universal curve of three-body binding energies versus scattering lengths is obtained efficiently by evolving a matrix renormalization group equation. In the latter example, exact solutions for the BCS-BEC crossover are obtained and the unexpected robust features in their excitation spectra are explained by a comprehensive semiclassical analysis.

In this thesis I explore the possibilities of detecting doubly charged Higgs bosons from the Higgs Triplet Model (HTM) at the Large Hadron Collider (LHC) at CERN. Higgs bosons are included into the Standard Model (SM) of particle physics in order to explain the origin of mass of the elementary particles. Even though the SM is considered to be a reliable starting point for any particle theory, no Higgs particles have to this day been found. There are therefore high expectations for the record-breaking energies of the LHC to lead to a Higgs discovery. The HTM produces seven different Higgs bosons, and among these we find the doubly charged ones. Because of their exotic charge, I focus on studying these Higgs particles in particular. To this purpose, I implement the full HTM theory as an alternative model option in standard particle physics Monte-Carlo software and then simulate LHC proton-proton collisions at a center of mass energy of 14 TeV. The investigated signal is defined as two like-signed leptons, four hard jets and missing energy in the final state. The main production mechanisms are pair-production and associated production with a singly charged Higgs. Since I choose to study a region of parameter space where the triplet vacuum expectation value is relatively large, the doubly charged Higgs decays into W's and the singly charged Higgs into WZ or tb. The results of the simulations show that the LHC could probe Higgs masses up to at least 300 GeV with an integrated luminosity of about 300 fb.1.

Reproduction de : Thèse de doctorat : Physique des particules : Lyon 1 : 2004. / Titre provenant de l'écran titre. 103 réf. bibliogr.

Thèse de doctorat : Physique des particules : Strasbourg : 2009. / Titre provenant de l'écran-titre. Bibliogr. 7 p.