No description available.

No description available.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: In this thesis, generalized Dyson boson-fermion mappings are considered. These are techniques used in the analysis of the quantum many-body problem, and are instances of so-called boson expansion methods. A generalized Dyson boson-fermion mapping, or a Dyson mapping for short, is a one-to-one linear but non-unitary operator that can be applied to vectors representing the states of a many-fermion system. A vector representing a fermion system maps onto a vector that is most naturally interpreted as representing a state of a many-body system that contains both bosons and fermions. The motivation for doing such a mapping is the hope that the mapping will reveal some property of the system that simplifies its analysis and that was hidden in the original form. The aims of this thesis are 1. to review the theory of generalized Dyson boson-fermion mappings, 2. by considering a tutorial example, to demonstrate that it is feasible to implement the theory and 3. to find a useful application for a generalized Dyson boson-fermion mapping, by considering a non-trivial model, namely the Richardson model for superconductivity. The realization of the first two aims mainly involve the collecting together of ideas that have already appeared in the literature, into one coherent text. Some subtle points that were treated only briefly due to space restrictions in the journal publications where the theory was first expounded, are elaborated on in the present work. On the other hand, the analysis of the Richardson Hamiltonian that uses a Dyson mapping, goes beyond what has already appeared in the literature. It is the first time that a boson expansion technique is implemented for a system where the roles of both collective and non-collective fermion pairs are important. (The Dyson mapping associates bosons with Cooper pairs, while the fermions not bound in Cooper pairs result in fermions being present in the mapped system as well.) What is found is that the Dyson mapping uncovers non-trivial properties of the system. These properties aid the construction of time-independent perturbation expansions for the stationary states of the system, as well as time-dependent expansions for transition amplitudes between states. The time-independent expansions agree with results that other authors obtained through methods other than boson expansions. The time-dependent expansions, that one would be hard-pressed to develop without a Dyson mapping, might in future prove useful in understanding aspects of the dynamics of ultracold fermi gases, when time-dependent magnetic fields are used to vary the atom-atom interaction strenght. / AFRIKAANSE OPSOMMING: In hierdie tesis word veralgemeende Dyson boson-fermion-afbeeldings ondersoek. Hierdie afbeeldings word gebruik in die analise van die kwantum veeldeeltjie probleem, en is voorbeelde van sogenaamde boson-uitbreidingstegnieke. 'n Veralgemeende Dyson bosonfermion- afbeelding, of kortweg 'n Dyson afbeelding, is 'n een-tot-een, lineêre maar nie-unitêre operator wat inwerk op vektore wat toestande verteenwoordig van 'n veel-fermion sisteem. 'n Vektor wat 'n fermionsisteem verteenwoordig word so afgebeeld op 'n vektor waarvoor die mees natuurlike interpretasie is dat dit 'n toestand verteenwoordig van 'n sisteem waarin beide bosone en fermione aanwesig is. So 'n afbeelding word gewoonlik gemaak in die hoop dat eienskappe van die sisteem, wat versteek was in die oorspronklike weergawe, voor-die-hand-liggend is na die afbeelding. Hierdie tesis het ten doel 1. om die teorie van veralgemeende Dyson boson-fermion-afbeeldings te hersien, 2. om 'n eenvoudige voorbeeld deur te werk, en so te demonstreer dat die teorie sonder moeite geïmplimenteer kan word en 3. om 'n nuttige toepassing te vind vir 'n veralgemeende Dyson boson-fermion-afbeelding deur 'n nie-triviale model, naamlik die Richardson model vir supergeleiding, te ondersoek. Die eerste twee van hierdie doelwitte behels hoofsaaklik dat idees wat reeds in die literatuur verskyn het, saamgevat word in een koherente teks. Sommige subtiele punte wat, vanwee beperkte ruimte, slegs kortliks bespreek is in die joernaalartikels waarin die teorie oorspronklik verskyn het, word in hierdie tesis meer breedvoering bespreek. Daarteenoor verteenwoordig die analise van die Richardson model met behulp van 'n Dyson afbeelding 'n nuwe bydra. Dit is naamlik die eerste keer dat 'n bosonuitbreiding ingespan word vir 'n sisteem waar sowel kollektiewe as nie-kollektiewe fermionpare 'n belangrike rol speel. (Die Dyson afbeelding assosieer bosone met die oorspronklike sisteem se Cooper pare, terwyl die fermione wat in die oorspronklike sisteem nie tot Cooper pare gebind is nie, sorg dat daar ook fermione teenwoordig is in die afgebeelde sisteem.) Ons vind dat die Dyson afbeelding nie-triviale eienskappe van die sisteem aan die lig bring. Hierdie eienskappe is nuttig vir die konstruksie van beide tyd-onafhanklike steuringsreekse vir die stasionêre toestande van die sisteem en vir tyd-afhanklike steuringsreekse vir oorgangsamplitudes tussen toestande. Die tyd-onafhanklike uitbreidings stem ooreen met resultate wat ander outeurs afgelei het sonder die gebruik van 'n Dyson afbeelding. Die tyd-afhanklike uitbreidings, wat kwalik afgelei kan word sonder 'n Dyson afbeelding, mag vorentoe nuttig wees om aspekte van die dinamika van baie koue Fermi gasse te verstaan, wanneer tydafhanklike magneetvelde gebruik word om die inter-atoomwisselwerking te manipuleer.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: We use Hanbury-Brown Twiss interferometry to determine Bose-Einstein correlations in the transverse and longitudinal directions. By using these two directions, we are able to determine the shape of the pion emitting source. The analysis is done with the UA1 (1985) data for pp collisions at Vs = 630 GeV. Two frames of reference, namely the laboratory frame and the Longitudinal Center-of-Mass System (LCMS) are used. A fit to a two-dimensional Gaussian parametrization yields good results. In the laboratory frame, an oblate form of the source is observed, with the value of the transverse radius (rt) larger than the longitudinal (rL) one. The LCMS analysis finds a prolate form of the source (rt < rL). A few reasons are discussed for the difference in the shape between the different reference frames. Our results are also compared with other hadron-hadron and e+ e: experiments. / AFRIKAANSE OPSOMMING: Hanbury-Brown Twiss interferometrie was gebruik om Bose-Einstein korrelasies in die transversale en longitudinale rigtings te bepaal. Deur hierdie twee rigtings te gebruik, kan die vorm van die pion-bron bepaal word. Die UA1 (1985) datastel van die pp botsings by Vs = 630 GeV is gebruik om die analise uit te voer. Twee verwysingstelsels, naamlik die laboratorium stelsel en die Longitudinale Massamiddelpunt-stelsel is aangewend. 'n Passing met 'n twee-dimensionele Gaussiese parametrisering het goeie resultate opgelewer. In die laboratorium stelsel, is 'n ovaalvormige vorm vir die bron waargeneem, met die transversale radius (rt) groter as die longitudinale radius (rl)' Die Longitudinale Massamiddelpunt stelsel het 'n prolate vorm vir die bron voorspel, met rt < ri, 'n Paar redes vir die verskil in die vorm van die pion-bron vir die verskillende verwysingstelsels word bespreek. Ons resultate word ook met ander hadron-hadron en e+e- eksperimente vergelyk.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: We present a theoretical approach that allows for the description of trapped Bose-Fermi mixtures with a tunable interspecies interaction in the vicinity of a Feshbach resonance magnetic field.The many-body physics of the system is treated at equilibrium using the well-established mean-field and local density approximations. This reduces the physics locally to that of a homogeneous system. We observe a rich local phase structure exhibiting both first and second order phase transitions between the normal and BEC phases. We also consider the global properties of the mixture at a fixed number of particles and investigate how the density profiles and the populations of the various particle species depend on the detuning and trap profile. / AFRIKAANSE OPSOMMING: Ons beskou ’n teoretiese beskrywing van gevangde Bose-Fermi mengsels met ’n verstelbare interspesie wisselwerking in die teenwoordigheid van ’n magneties-geïnduseerde Feshbach resonansie. Die veeldeeltjiefisika van die sisteem word by ekwilibrium binne die welbekende gemiddelde-veld en lokale-digtheid benaderings hanteer. Sodoende word die fisika lokaal tot die van ’n homogene sisteem gereduseer. Ons neem ’n ryk fase-struktuur waar met beide eerste- en tweede-orde fase-oorgange tussen die normale en BEK fases. Ons beskou ook die globale eienskappe van die mengsel by ’n vaste totale aantal deeltjies en ondersoek hoe die digtheidsprofiele en deeltjiegetalle van die afstemming en die profiel van die val afhang.

No description available.

This thesis presents measurements of charged current deep inelastic scattering cross sections in e+p collisions with longitudinally polarised positron beams. The measurements are based on data taken by the ZEUS detector at the HERA collider during the 2006-2007 run- ning period. The data sample has an integrated luminosity of 132 pb-1 and was taken at a centre-of-mass energy of 318 GeY. The total cross section has been measured at positive and negative values of the longitu- dinal polarisation of the positron beam (Pe). In addition, the single differential cross sections dδ / dQ2, dδ / dx and dδ / dy have been measured for Q2 > 200 Ge y2, also using both positively and negatively polarised positron beams. The reduced cross section has been measured in nine bins of Q2 in the kinematic range 280 < Q2 < 30000 Gey2 and 0.0078 < x < 0.42. The results are compared against the descriptions provided by the CTEQ6.6, MSTW 2008, HEARPDF1.0 and ZEUS-JETS PDFs. In general, the measured cross sections are well described by these predictions. Based on the measurement of the total cross section as a function of the polarisation of the positron beam, a lower limit on the mass of a hypothetical right-handed W boson has been extracted from the upper limit of the cross-section at Pe = -1. This limit is complementary to the limits obtained from direct searches (for example at CDF and D0) because the limit presented herein is for a space-like vV, whereas for direct searches, the limit on the mass of a time-like W boson is obtained. The results of this analysis have been published and have been included ill the determination of the HERAPDF theoretical prediction and also in HI and ZEUS combined results.

A thesis submitted to the Faculty of Science University of the Witwatersrand Johannesburg in fulfillment of the requirements for the Master of Science Johannesburg 1997

Thesis presented in fulfilment of the requirements for the degree of Master of Science in Physics at the University of the Witwatersrand School of Physics, University of the Witwatersrand, 2015. / A search for the pseudoscalar A boson, which is predicted by in many models with an extended Higgs sector, gives a gateway to searches for physics beyond the Standard Model (SM). This thesis presents the results of a search for gluon-fusion produced A in the decay to Zh, with a final state of two electrons or muons and two τ leptons, in 20.3 fb−1of proton-proton collision data at √s = 8 TeV. Each tau lepton is allowed to dacay either leptonically, τlep, or hadronically,τhad, giving rise to three final states, τlepτlep, τlepτhad and τhadτhad. Focus is placed on the methodology and results of the fully hadronic channel. No evidence for the existence of an A boson is found in the scanned range of 220 ≤ mA ≤ 1000 GeV and 95% CL upper limits are placed on the gluon-fusion cross section times branching ratio, σ × BR(A → Zh) × BR(h → ℓℓττ). The results are combined with a complementing A → Zh search, where h → b¯b, and interpreted in view of two-Higgs-Doublet-Models (2HDMs), where exclusion limits are placed on large sections of phasepace.

Neste trabalho estudou-se a fenomenologia da observação de novos bósons vetoriais com massa da ordem de 1 TeV no LHC. Em particular, a análise foi feita para um bóson vetorial neutro que se acopla com os bósons carregados do Modelo Padrão e esses bósons decaem hadronicamente deixando uma assinatura com jatos no detector. Esse tipo de sinal possui um enorme fundo de QCD devido ao ambiente hadrônico intrínseco ao LHC, de maneira que o uso de técnicas de análise de subestrutura de jatos se tornam indispensáveis. A motivação do trabalho vem dos modelos com dimensões extras curvas que possuem torres de Kaluza-Klein de novos bósons de gauge. Estes são responsáveis por garantir a unitariedade nos espalhamentos dos bósons vetoriais do MP, estudamos em especial a primeira excitação do \'Z POT. 0\', o bóson \'Z POT. 1\'. Na análise fenomenológica vericamos que o LHC possui um grande potencial de descoberta e exclusão dessas classes de modelos além do MP. Para tanto estudamos o sinal pp -> \'Z POT. 1\' -> WW -> jatos e os processos do MP do tipo pp -> jatos, com pelo menos dois jatos na janela de massa do W. Vericamos que para um \'Z POT. 1\' de largura \'M IND. z \'IND. 1\'/10, com massa da ordem de 1 TeV e acoplamentos da ordem de \'10 POT. 3\' vezes menores que os acoplamentos do MP é possível observá-lo no LHC com 30 \'fb IND. -1\' de luminosidade integrada com 14 TeV de energia no centro de massa. / In this work we present a phenomenological study of the observation of new vector bosons with mass around 1 TeV at the LHC. We analyse a neutral vector boson that couples to the charged bosons of the Standard Model and this bosons decay hadronically leaving a multiple jets signature on the detector. This kind of signal has an enormous QCD background due to the hadronic enviroment of the LHC, making the analysis of jet substruture indispensable. The motivation for this work comes from warped extra dimensions models, wich have Kaluza-Klein towers of new gauge bosons. These are responsable for assuring the unitarity of the vector bosons scatterings in the SM. We studied the first excitation of the Z0 bosons, the Z1 boson. We veried that the LHC has a great potential of discovery or exclusion for this classes of theories beyond the SM. For the analysis, we studied the process pp -> Z1 -> WW -> jets and the background processes of the SM of the type pp -> jets, with at least two jets in the W mass window. We veried that for a Z1 with width MZ1/10 , mass of O(1 TeV) and couplings 10^3 times more weakly than those of the SM, it is possible to observe it in the LHC with 30 fb-1 of integrated luminosity in the 14 TeV run.