Ho Lai-yin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 53-56). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Peierls Transition --- p.3 / Chapter 2.1 --- The Start of the Idea --- p.3 / Chapter 2.2 --- Peierls Transition in Second Quantization Representation --- p.5 / Chapter 2.3 --- Effect of Peierls Transition on an Antiferromagnetic Chain --- p.6 / Chapter 2.4 --- Evidence of Spin-Peierls Transition --- p.9 / Chapter 2.5 --- Materials with Spin-Peierls Transition --- p.11 / Chapter 3 --- Mean Field Calculations --- p.15 / Chapter 3.1 --- Jordan-Wigner Transformation --- p.15 / Chapter 3.2 --- Diagonalization of the XY Model --- p.17 / Chapter 3.3 --- Hartree-Fock Approximation --- p.19 / Chapter 3.4 --- Quantum Effect of Lattice --- p.21 / Chapter 4 --- Bosonization --- p.25 / Chapter 4.1 --- Continuum Limit --- p.25 / Chapter 4.2 --- Bosonization --- p.28 / Chapter 4.3 --- Relaxation of the Restriction on Lattice Distortion --- p.36 / Chapter 4.4 --- More Discussion on the Phase Hamiltonian --- p.39 / Chapter 4.5 --- Limitation of the Bosonization Technique and the Phase Hamil- tonian Approach --- p.41 / Chapter 5 --- Effect of Doping Impurities on Spin-Peierls Model --- p.43 / Chapter 5.1 --- Experimental Results --- p.43 / Chapter 5.2 --- Analytical Calculations of Doping Effect --- p.44 / Chapter 5.3 --- Criticism on the Calculations --- p.50 / Chapter 6 --- Summary and Conclusions --- p.52 / Bibliography --- p.53 / Chapter A --- Random-Phase Approximation --- p.57

Searches are made for narrow diboson resonances, ZZ and ZW, in the final states llqq and ννqq at ATLAS, with (13.2±0.4) fb−1data collected from pp-collisions with center of mass energy √ s=13 TeV during 2015 and 2016, the first two years of Run 2 of the Large Hadron Collider. The hadronic decay products of the vector boson, V → qq, are reconstructed as jets in the electromagnetic and hadronic calorimeters. When the vector boson is sufficiently boosted the decay products are reconstructed as a single anti-kt R = 1.0 jet. Otherwise two anti-kt R = 0.4 jets are matched to identify the vector boson. The Z boson in its leptonic decay is identified by either reconstructing two electrons in the calorimeters, or opposite sign muons in the muon spectrometer. Limits on the production cross section for 3 benchmark signals, a heavy scalar, a spin-1 heavy vector triplet, and a spin-2 graviton are set in the mass range 300 GeV to 5000 GeV.

A search is presented for new resonances decaying to a pair of boosted Standard Model bosons, WV, where the W boson decays leptonically (W → lν, with l = e, µ) and the other weak boson, V (V=W,Z), decays hadronically (V → qq¯ 0/qq¯, with q, q0 = u, d, c, s, b). The data were collected with the ATLAS detector at the CERN Large Hadron Collider, during the 2015 and 2016 periods of pp collisions, at a center-of-mass energy √s = 13 TeV, and correspond to a total integrated luminosity of 36.1 fb^−1. The hadronic decay of the boosted $V$ boson is reconstructed as a single large-radius jet, and the leptonic decay of the W boson is reconstructed as a lepton and missing transverse energy. The search is sensitive to resonances produced with quark-antiquark fusion, gluon-gluon fusion, and vector-boson fusion. No significant excesses are observed above the Standard Model background prediction. Upper limits on production cross section times branching ratio to WV are set at a 95 % confidence level for selected benchmark signal models. Models of a neutral, narrow scalar boson (spin-0), charged and neutral vector bosons (spin-1) coupling to the Standard Model gauge bosons, and a neutral Randall-Sundrum bulk graviton (spin-2) are considered. The search significantly improves the limits produced in recent searches.

No description available.

La Cromodinàmica Quàntica (QCD) és la teoria de camps que descriu les interaccions fortes entre quarks i gluons. La signatura més destacada de QCD en col·lisionadors hadrúnics és la producció de jets col·limats d'hadrons. La mesura de la producció d'aquests jets associats amb un bosó vectorial, W o Z/gamma*, proporciona un test estricte dels càlculs pertorbatius de QCD (pQCD). A més a més, alguns processos de nova física en col·lisionadors hadrúnics, com ara la producciÓ del bosó de Higgs i partícules supersimètriques, poden ser molt semblants a la producció de bosons vectorial associats amb jets que constitueixen un fons irreductible en aquestes cerques. Per tant l'estudi i comprensió de processos Z/gamma*+jets és una part crucial del programa de física del col·lisionador Tevatron. Durant el Run I del Tevatron, protons i antiprotons col·lidien amb una energia en el centre de masses sqrt(s) de 1.8 TeV. La producciÓ de Z/gamma*+jets es va estudiar durant el Run I amb el detector CDF utilitzant 106 pb-1 de dades. Les mesures es van comparar amb les prediccions de l'ordre més baix en teoria de pertorbacions (LO) més parton shower d'alguns generadors de Monte Carlo. Les comparacions estaven dominades per les grans incerteses en les prediccions de LO. En el Run II, el Tevatron i el detector CDF es van millorar i, entre d'altres importants millores, sqrt(s) es va augmentar a 1.96 TeV. El bon funcionament de l'accelerador i del detector van proporcionar una quantitat més gran de dades que va fer possible mesures diferencials de gran precisió.Aquesta tesi doctoral presenta la mesura de seccions eficaces inclusives de jets en esdeveniments amb Z/gamma*->ee utilitzant 1.7 fb-1 de dades obtingudes amb el detector CDF durant el Run II del Tevatron. L'algoritme de con Midpoint s'ha utilitzat per a buscar jets en els esdeveniments després d'haver identificat la presència d'un bosó Z/gamma* a través de la reconstrucció dels productes de la seva desintegració. Les mesures s'han comparat amb les prediccions del següent nivell (NLO) en pQCD per esdeveniments amb un o dos jets en l'estat final. Les prediccions pertorbatives s'han corregit per les contribucions de processos no-pertorbatius, com l'underlying event i la fragmentació dels partons en jets d'hadrons. Aquests processos no són descrits per la teoria de pertorbacions i s'han d'estimar amb models fenomenològics. En aquesta tesi, s'han realitzat un conjunt de mesures per a testejar diferents models d'underlying event i hadronització implementats en programes de Monte Carlo de LO més parton shower. / Quantum Chromodynamics (QCD) is the field theory that describes the strong interactions between quarks and gluons. The most prominent signature of QCD at hadron colliders is the production of collimated jets of hadrons. The measurement of the production of such jets in association with a vector boson, W or Z/gamma*, provides an stringent test of perturbative QCD (pQCD) calculations. Furthermore, some of new physics processes at hadron colliders, such as the production of Higgs bosons and supersymmetric particles, can be mimicked by the production of vector bosons in association with jets that constitute irreducible backgrounds to these searches. Therefore, the study and understanding of Z/gamma*+jets processes is a crucial part of the physics program of the Tevatron collider. At the Run I of the Tevatron, protons and antiprotons collided with an energy in the center-of-mass ps of 1.8 TeV. Z/gamma*+ jets production was studied during Run I with the CDF detector using 106 pb-1 of data. The measurements were compared to the predictions from leading order (LO) plus parton shower Monte Carlo generator programs. The comparisons were mainly dominated by the large scale uncertainties in the LO predictions. In Run II, the Tevatron and the CDF detector were upgraded and, among other important improvements, sqrt(s) was increased to 1.96 TeV. The good performance of the accelerator and the detector made available a larger amount of data, making possible precise differential measurements.This Ph.D. thesis presents the measurement of inclusive jet cross sections in Z/gamma*(->ee) events using 1.7 fb-1 of data collected by the upgraded CDF detector during the Run II of the Tevatron. The Midpoint cone algorithm is used to search for jets in the events after identifying the presence of a Z/gamma* boson through the reconstruction of its decay products. The measurements are compared to next-to-LO (NLO) pQCD predictions for events with one and two jets in the final state. The perturbative predictions are corrected for the contributions of non-perturbative processes, like the underlying event and the fragmentation of the partons into jets of hadrons. These processes are not described by perturbation theory and must be estimated from phenomenological models. In this thesis, a number of measurements are performed to test different models of underlying event and hadronization implemented in LO plus parton shower Monte Carlo generator programs.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 52-54). Also available online.

Thèse doctorat : Physique Théorique : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr. 5 p.

Reproduction de : Thèse de doctorat : Physique nucléaire : Lyon 1 : 2002. / Titre provenant de l'écran titre. 85 réf. bibliogr.

If there is a general theme to this thesis, it is the effects of strong correlations in both bosons and fermions. The bosonic system considered here consists of ultracold alkali atoms trapped by interfering lasers, so called optical lattices. Strong interactions, realized by increasing the depth of the lattice potential, or through the phenomenon of Feshbach resonances induce strong correlations amongst the atoms, rendering attempts to describe the systems in terms of single particle type physics unsuccessful. Of course strong correlations are not the exclusive domain of bosons, and also are not caused only by strong interactions. Other factors such as reduced dimensionality, in one-dimensional electron gases, or strong magnetic fields, in two-dimensional electron gases are known to induce strong correlations. In this thesis, we explore the manifestations of strong correlations in ultracold atoms in optical lattices and interacting electron gases. Optical lattices provide a near-perfect realization of lattice models, such as the bosonic Hubbard model (BHM) that have been formulated to study solid state systems. This follows from the absence of defects or impurities that usually plague real solid state systems. Another novel feature of optical lattices is the unprecedented control experimenters have in tuning the different lattice parameters, such as the lattice spacing and the intensity of the lasers. This control enables one to study the model Hamiltonians over a wide range of variables, such as the interaction strength between the atoms, thereby opening the door towards the observation of diverse and interesting phenomena. The BHM, and also its variants, predict various quantum phases, such as the strongly correlated Mott insulator (MI) phase that appears as a function of the parameter t/U, the ratio of the nearest neighbor hopping amplitude to the on-site interaction, which one varies experimentally over a wide range of values simply by switching the intensity of the lasers. But as always, even in these designer-made "solid state" systems, practical considerations introduce complications that blur the theoretical interpretation of experimental results, such as inhomogeneities in the lattice structure. The first part of this thesis presents a quantum theory of ultracold bosonic atoms in optical lattices capable of describing the properties of the various phases and the transitions between them. Its usefulness, compared to other approaches, we believe rests in its broad applicability and in the relative ease it handles the complications while producing quantitatively accurate results. / text

Geometric quantization is a subject of finding irreducible representations of certain group or algebra and identifying those equivalent representations by geometric means. Geometric quantization of even dimensional fermionic system has been constructed based on the spinor representation of even dimensional Clifford algebras. Although geometric quantization of odd dimensional fermionic system has not been done, the existence of spinor representations in odd dimension indicates that the geometric quantization is possible. In quantum field theory, charge conjungation can be defined on complex bosons and fermions. Without interaction, the particles and anti-particles essentially have same physical properties. In this thesis, we will first recall the setup of geometric quantization of even dimensional fermion and bosons. Then we will show how to quantize odd dimensional fermion. After that, charge conjungation on complex fermion and boson will be defined and the remaining effort will be put on how to identify the Hilbert spaces produced by different charge conjungations. / published_or_final_version / Mathematics / Master / Master of Philosophy