We present a study of e⁺e⁻ collisions where only photons are visible in the final state in data taken with the AMY detector at TRISTAN. Data are presented at CM energies from 50 to 64 GeV, with a total integrated luminosity of 189.1 pb⁻¹. Differential cross sections for e⁺e⁻ → γγ, γγγ are measured and compared to 𝛰(α³) QED. A search for electron compositeness through an e⁺e⁻ γγ contact interaction is conducted, and limits are presented. A search for the pair production of unstable photinos is also presented with limits. Finally, the result of a search for anomalous γγ production is presented, based upon energy scan data taken in December, 1992. / Ph. D.

In dieser Arbeit wird eine systematische Methode gegeben um die Amplituden in (skalarer) Quantenelektrodynamik und nicht-Abelsche Eichtheorien in Schwinger-parametrische Form zu schreiben. Dies wird erreicht in dem der Zähler der Feynmanregeln im Impulsraum in einem Differentialoperator umgewandelt wird. Dieser Differentialoperator wirkt dann auf den parametrichen Integranden der skalaren Theorie. Für die QED ist das am einfachsten, weil die Leibnizregel hier nicht nötig ist. Im Fall der sQED und den nicht-Abelsche Eichtheorien stehen die Beiträge der Leibnizregel in Verbindung mit 4-valente Vertices. Eine andere Eigenschaft dieser Methode ist, dass mit dem hier benutzten Renormierungsschema die Subtraktionen für 1-scale Graphen signifikante Vereinfachungen verursachen. Weiterhin wurden die Ward-Identitäte für die genannten drei Theorien studiert. / In this thesis a systematic method is given for writing the amplitudes in (scalar) quantum electrodynamics and non-Abelian gauge theories in Schwinger parametric form. This is done by turning the numerator of the Feynman rules in momentum space into a differential operator. It acts then on the parametric integrand of the scalar theory. For QED it is the most straightforward, because the Leibniz rule is not involved here. In the case of sQED and non-Abelian gauge theories, the contributions from the Leibniz rule are satisfyingly related to 4-valent vertices. Another feature of this method is that in the used renormalization scheme, the subtractions for 1-scale graphs cause significant simplifications. Furthermore, the Ward identities for mentioned three theories are studied.

Thesis (MSc (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See abstract in full text / AFRIKAANSE OPSOMMING: Sien opsomming in volteks

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It is possible to reach the radiation-reaction–dominated regime in today’s high-intensity laser facilities, using the collision of a wakefield-accelerated GeV electron beam with a 30 fs laser pulse of intensity 10²² Wcm^-2. This would demonstrate that the yield of high energy gamma rays is increased by the stochastic nature of photon emission: a beam of 10⁹ electrons will emit 6300 photons with energy > 700 MeV, 60 times the number predicted classically. Detecting those photons, or a prominent low energy peak in the electron beam's post-collision energy spectrum, will provide strong evidence of quantum radiation reaction; we place constraints on the accuracy of timing necessary to achieve this. This experiment would provide benchmarking for the simulations that will be used to study the plasmas produced in the next generation of laser facilities. With focused intensities > 10²³ Wcm^-2, these will be powerful enough to generate high fluxes of gamma rays and electron-positron pairs from laser–laser and laser–solid interactions. It will become possible to test the physics of exotic astrophysical phenomena, such as pair cascades in pulsar magnetospheres, and explore fundamental aspects of quantum electrodynamics (QED). To that end we will discuss: classical theories of radiation reaction; QED processes in intense fields; and a Monte Carlo algorithm by which the latter may be included in particle-in-cell codes. The feedback between QED processes and classical plasma dynamics characterises a new regime we call QED-plasma physics.

Apresento neste trabalho uma derivação alternativa da hamiltoniana efetiva para um elétron na banda de condução de uma heteroestrutura semicondutora de rede Zincblende. Partindo do modelo de Kane 8 × 8 e da aproximação das funções envelope, esta hamiltoniana efetiva foi obtida com a linearização dos denominadores (dependentes das autoenergias) presentes na equação para a banda de condução, sob a hipótese de que o gap de energia seja muito maior que todas as demais diferenças de energia envolvidas (verdade para a maioria das estruturas Zincblende). A partir de um procedimento introduzido previamente1,3, desenvolvi um procedimento mais geral que implementa sistematicamente esta linearização até segunda ordem no inverso do gap de energia e que corrige a normalização do spinor da banda de condução usando as bandas de valência. Este procedimento é idêntico à expansão em série de potência no inverso da velocidade da luz utilizada para se obter aproximações relativísticas da equação de Dirac. Uma vantagem deste procedimento é a arbitrariedade na forma dos potenciais, o que implica na validade da hamiltoniana resultante para poços, fios e pontos quânticos. Evidencio também as consequências de cada termo desta hamiltoniana efetiva para os autoestados eletrônicos em poços retangulares, incluindo termos independentes de spin inéditos (Darwin e interação momento linearcampo elétrico). Estes resultados estão de acordo com os estudos anteriores4. A fim de estudar transições ópticas dentro da banda de condução, mostro que o acoplamento mínimo pode ser realizado diretamente na hamiltoniana de Kane se os campos externos variam tão lentamente quanto as funções envelope. Repetindo a linearização dos denominadores de energia, derivo uma hamiltoniana efetiva para a banda de condução com acoplamentos elétron-fótons. Um destes acoplamentos, induzido exclusivamente pela banda de valência, origina transições mediadas pelo spin eletrônico. Estas transições assistidas por spin possibilitam mudanças, opticamente induzidas, na orientação do spin eletrônico, um fato que talvez possa ser útil na construção de dispositivos spintrônicos. Por fim, as taxas de transição deste acoplamento apresentam saturação e linhas de máximos e mínimos no espaço recíproco. Espero que estas acoplamentos ópticos possam auxiliar na observação dos efeitos dos acoplamentos spin-órbita intra (Rashba) e intersubbandas. / In this work, I present an alternative derivation of the conduction band effective hamiltonian for Zincblende semiconductor heterostructures. Starting from the 8×8 Kane model and envelope function approximation, this effective hamiltonian was obtained by means of a linearization in the eigenenergy-dependent denominators present the conduction band equation, under the hypothesis that the energy gap is bigger than any other energy difference in the system (true for mostly every Zincblende semiconductor bulk or heterostructure). Based on a previous procedure1,3, I have developed a more general procedure that implements sistematicaly (i) this linearization and (ii) renormalizes the conduction band spinor using the valence bands, both (i) and (ii) up to second order in the inverse of the energy gap. This procedure is identical to the expansion in power series of the inverse of the light speed used to derive non-relativistic approximations of the Dirac equation. One advantage of this procedure is the generality of the potentials adopted in our derivation: the same results hold for quantum wells, wires and dots. I show the consequences of each term of this hamiltonian for the electron eigenstates in retangular wells, including novel spin-independent terms (Darwin and linear momentumelectric field couplings). These resulties agree with previous works4. In order to study conduction band optical transitions, I show that the minimal substitution can be performed directly in the Kane hamiltonian if the external fields vary slowly (at least, as slowly as the envelope functions). Repeating the linearization of the energy denominators, I derive a new effective hamiltonian, up to second order in the inverse of the energy gap, with electron-photons couplings. One of these couplings, induced exclusively by the valence bands, gives rise to optical transitions mediated by the electron spin. This spin-assisted coupling enable optically-induced spin flipps in conduction subband transitions, which can be useful in the construction of spintronic devices. Finaly, the spin-assisted transitions rates show saturation and lines of maxima and minima in the reciprocal lattice. I hope that these optical couplings can be of any help in the observation of interesting effects induced by the intra and intersubband spin-orbit coupling.

Estudamos neste trabalho as contribuições de 1-loop da eletrodinâmica quântica não-comutativa a altas temperaturas. Obtivemos as amplitudes de n-pontos por meio do método de diagramas de Feynman e mostramos que os mesmos resultados podem ser obtidos pelo método das equações de transporte de Boltzmann. Em paralelo estudamos as massas de blindagem que seguem do setor não-comutativo da teoria no limite estático, assim como a ação efetiva em 1-loop que gera todas as funções de n-pontos com índices espaciais. Também estudamos a quantização do campo de gauge no espaço não-comutativo pelo método do campo de fundo, obtendo uma generalização da base de ondas planas que se transforma covariantemente. / In this work we study the 1-loop contributions for noncommutative electrodynamics at high temperature. We calculate the n-point amplitudes by the Feynman diagrams method and we show that the same results can be obtained by the method of Boltzmann transport equations. We also study the screening mass derived from the noncommutative sector in the static limit case and the effective generating functional that determine all the amplitudes at one loop with spatial indices only. We quantize noncommutative QED by the background field gauge method and obtain a generalization of plane waves that transforms covariantly.

全光信息處理被認為是其中一種改善當今計算機網絡性能的方法。而高效率的全光信息處理需要使用可用低強度的控制激光來控制的全光學開關。最近有人提出利用橫向光學圖案製造低強度全光學開關，並已通過原子蒸氣系統的實驗證明這個計劃的可行性。此外，相關的研究正在半導體量子阱微腔中進行。 / 這篇論文以微觀多體理論研究被激光正向入射的半導體量子阱微腔系統中產生的自發性橫向光學圖案。入射光會在一定條件下於半導體量子阱微腔中發生極化子場之間的自發四波混頻，並產生橫向光學圖案。我們分別以半分析和數值模擬的方法研究這些圖案的形成和選擇方式。本論文亦研究了如何用離軸激光和腔的各向異性來控制這些圖案。 / 我們分別用「多- / Processing information all-optically is thought to be one way to improve the performance of present-day computational network. Low intensity all-optical switches are desirable for effective all-optical information processing. Recently, low intensity all-optical switching schemes utilizing transverse optical patterns have been proposed. One such scheme was successfully demonstrated experimentally in an atomic vapour system, and a similar scheme is being studied both theoretically and experimentally in semiconductor quantum well micro-cavities. / In this thesis, we present our theoretical studies on the spontaneous transverse optical patterns produced by a semiconductor quantum well microcavity, pumped by a normally incident laser, using a microscopic many-body theory. Far field transverse optical patterns are formed under certain conditions by spontaneous four-wave mixing of the exciton-photon polariton field. The formation and the selection of these patterns are studied by both semi-analytical calculations and numerical simulations. The controls of transverse patterns using anisotropy in the microcavity and an o-axis control beam are also being studied in this thesis. / Two reduced models, the ‘multi- / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Luk, Ming Ho = 對半導體量子阱微腔中橫向光學圖案的控制 / 陸名浩. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 136-141). / Abstracts also in Chinese. / Luk, Ming Ho = Dui ban dao ti liang zi jing wei qiang zhong heng xiang guang xue tu an de kong zhi / Lu Minghao. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Pattern formation and nonlinear optics --- p.5 / Chapter 1.2 --- All-optical switching --- p.8 / Chapter 1.3 --- Semiconductor quantum well microcavity --- p.9 / Chapter 2 --- Semiconductor quantum well microcavity --- p.13 / Chapter 2.1 --- The structure of semiconductor quantum well microcavity --- p.14 / Chapter 2.2 --- Coupling between the cavity mode and external fields --- p.18 / Chapter 2.3 --- Microscopic theory in the microcavity --- p.22 / Chapter 3 --- Linear stability analysis and reduced models --- p.32 / Chapter 3.1 --- Pump only system - steady state solution --- p.32 / Chapter 3.2 --- Pump only system - stability analysis --- p.37 / Chapter 3.3 --- Off-axis stability studies --- p.39 / Chapter 3.3.1 --- Stability analysis without phase-space filling --- p.40 / Chapter 3.3.2 --- Linear stability analysis with phase-space filling --- p.54 / Chapter 3.4 --- Reduced models --- p.59 / Chapter 3.4.1 --- The multi- --- p.63 / Chapter 3.4.2 --- The ring model --- p.68 / Chapter 3.5 --- Effects of system parameters --- p.71 / Chapter 3.5.1 --- Radiative loss --- p.72 / Chapter 3.5.2 --- Incident laser field/intensity --- p.73 / Chapter 3.5.3 --- Fluctuations/weak constant sources --- p.78 / Chapter 4 --- Single-hexagon model --- p.82 / Chapter 4.1 --- Numerical results of single-hexagon model --- p.82 / Chapter 4.2 --- Pattern and time scale variations with parameters --- p.86 / Chapter 4.2.1 --- Anisotropy in the cavity mode energy --- p.87 / Chapter 4.2.2 --- Control beam intensity --- p.90 / Chapter 5 --- Dynamical analysis and interplay of wave-mixing processes --- p.93 / Chapter 5.1 --- Dynamical analysis --- p.93 / Chapter 5.2 --- Interplay of wave mixing processes --- p.99 / Chapter 5.3 --- Switching between hexagons --- p.103 / Chapter 6 --- Full two-dimensional simulation --- p.111 / Chapter 6.1 --- Convolution theorem and Fast Fourier Transform --- p.112 / Chapter 6.2 --- Simulation result and difficulties --- p.114 / Chapter 7 --- Other approaches --- p.119 / Chapter 7.1 --- Real Space Simulation --- p.119 / Chapter 7.2 --- Mode competition model --- p.121 / Chapter 7.3 --- Transfer Matrix --- p.123 / Chapter 8 --- Conclusion and outlook --- p.125 / Chapter 8.1 --- Future work --- p.128 / Chapter 8.1.1 --- Double Cavities --- p.128 / Chapter 8.1.2 --- The Gross-Pitaevskii Equation and Bose-Einstein Condensation --- p.131 / Bibliography --- p.136 / Chapter A --- Dispersion of cavity photon --- p.142