Decay widths and scattering processes in massive QED2_2

Using mass perturbation theory, we infer the bound-state spectrum of massive QED$_2$ and compute some decay widths of unstable bound states. Further, we discuss scattering processes, where all the resonances and particle production thresholds are properly taken into account by our methods.Comment: Latex file, 5 pages, 8 ps-figures & 1 style-file; written version of a talk given at the QCD97 conference in Montpellier, Franc

Decay widths in the massive Schwinger model

By a closer inspection of the massive Schwinger model within mass perturbation theory we find that, in addition to the $n$-boson bound states, a further type of hybrid bound states has to be included into the model. Further we explicitly compute the decay widths of the three-boson bound state and of the lightest hybrid bound state.Comment: 8 pages, Latex file, no figure

General bound-state structure of the massive Schwinger model

Within the Euclidean path integral and mass perturbation theory we derive, from the Dyson-Schwinger equations of the massive Schwinger model, a general formula that incorporates, for sufficiently small fermion mass, all the bound-state mass poles of the massive Schwinger model. As an illustration we perturbatively compute the masses of the three lowest bound states.Comment: 11 pages, 7 figures, needed macro: psbox.te

Normalization of the chiral condensate in the massive Schwinger model

Within mass perturbation theory, already the first order contribution to the chiral condensate of the massive Schwinger model is UV divergent. We discuss the problem of choosing a proper normalization and, by making use of some bosonization results, we are able to choose a normalization so that the resulting chiral condensate may be compared, e.g., with lattice data.Comment: Latex file, 8 pages, 1 figure, needed macro: psbox.te

The Schwinger Mass in the Massive Schwinger Model

We derive a systematic procedure to compute Green functions for the massive Schwinger model via a perturbation expansion in the fermion mass. The known exact solution of the massless Schwinger model is used as a starting point. We compute the corrections to the Schwinger mass up to second order.Comment: Latex, 7 pages, no figure

An interactive triangle approach to student learning

Report of a CELT project on enhancing learning and teaching through innovation and research.Discusses the findings of a research project designed to improve student performance through innovative learning and teaching methods. The traditional format of the Human Physiology module (a core module in the Biomedical Science portfolio) comprising a weekly programme of two lectures and one tutorial was replaced by converting lectures into an on-line form and hosting them on the University's virtual learning environment (WOLF), linking these to key texts, on-line resources and computer software packages. Workshops and drop-in sessions provided additional support and an opportunity for lecturers to diagnose areas of difficulty and provide strategies for resolving them

Forecast performance of implied volatility and the impact of the volatility risk premium

Forecasting volatility has received a great deal of research attention, with the relative performance of econometric models based on time-series data and option implied volatility forecasts often being considered. While many studies find that implied volatility is the preferred approach, a number of issues remain unresolved. Implied volatilities are risk-neutral forecasts of spot volatility, whereas time-series models are estimated on risk-adjusted or real world data of the underlying. Recently, an intuitive method has been proposed to adjust these risk-neutral forecasts into their risk-adjusted equivalents, possibly improving on their forecast accuracy. By utilising recent econometric advances, this paper considers whether these risk-adjusted forecasts are statistically superior to the unadjusted forecasts, as well as a wide range of model based forecasts. It is found that an unadjusted risk-neutral implied volatility is an inferior forecast. However, after adjusting for the risk premia it is of equal predictive accuracy relative to a number of model based forecasts.Implied volatility, volatility forecasts, volatility models, volatility risk premium, model confidence sets

Vacuum Cherenkov radiation and photon triple-splitting in a Lorentz-noninvariant extension of quantum electrodynamics

We consider a CPT-noninvariant scalar model and a modified version of quantum electrodynamics with an additional photonic Chern-Simons-like term in the action. In both cases, the Lorentz violation traces back to a spacelike background vector. The effects of the modified field equations and dispersion relations on the kinematics and dynamics of decay processes are discussed, first for the simple scalar model and then for modified quantum electrodynamics. The decay widths for electron Cherenkov radiation in modified quantum electrodynamics and for photon triple-splitting in the corresponding low-energy effective theory are obtained to lowest order in the electromagnetic coupling constant. A conjecture for the high-energy limit of the photon-triple-splitting decay width at tree level is also presented.Comment: elsart, 30 pages, v4: published versio

Material and Process Engineering for Bulk Single Crystal Growth of High Performance Scintillator Potassium Calcium Iodide

Protection against threats of nuclear terrorism relies on the deployment of an enormous number of radiation detection devices with energy resolution to differentiate the radiological signatures of special nuclear materials amongst naturally occurring radiation and other nuisance sources. The capabilities of these devices rely upon the availability of high performance scintillator and semiconductor materials which provide useful responses in the presence of radiation. So far, few materials have been developed to a level that can supplant the use of underperforming NaI:Tl [thallium doped sodium iodide] crystals in the field due to their high cost and/or low yields of production. KCaI3[potassium calcium tri-iodide] doped with divalent europium has shown significant promise as a high performance scintillator and development to explore its potential for large scale production is necessary. KCaI3 crystallizes into an orthorhombic symmetry and exhibits a moderate amount of anisotropy in thermal expansion between its melting point of 524°C [Celsius] and room temperature. Production of large single crystals up to 1.5” in diameter can be facilitated through the vertical Bridgman method of melt growth using pyrolytic carbon-coated ampoules which eliminate cracking upon cooling. Low dopant amounts of 0.5-1.0 at% of Eu can achieve excellent energy resolutions of 3-4% at 662 keV while minimizing deleterious self-absorption effects, making it comparable to the highest performing scintillators discovered. A purpose-built multi-ampoule growth station was constructed and through the course of the investigation, a process was developed whereby several high quality, uncracked KCaI3 crystals at 1” in diameter could be grown simultaneously, in parallel, using a randomly oriented self-seeded approach. The demonstration shows great promise as a potential pathway to reduce the costs of scintillator production that is limited to a large number of boules at the 1”- 2” diameter size. Furthermore, KCaI3 possesses internal radioactivity due to the presence of naturally abundant 40K [potassium – 40] and will restrict its utility to applications where an elevated background is not critical. A significant obstacle to production of KCaI3 crystals doped with europium is the uniform distribution of the activator which can result in concentration gradients in bulk crystals and degrade spectroscopic performance

Novel surface proteins in the pathogenesis and diagnosis of Lyme disease

Lyme disease is caused by an infection with the spirochete Borrelia burgdorferi. Transmitted between mammal reservoirs by the bite of an Ixodes tick, the pathogen exists in a complex life cycle that requires long-term persistence in arthropod and mammal hosts. The mechanisms responsible for persistence and the pathogenesis of Lyme disease are not well understood, but may involve interactions between bacterial surface proteins and the host. Previous experiments have shown that differential gene expression of surface proteins assists the pathogen in adaptation and persistence in a new host. Most B. burgdorferi surface proteins have no homology to known proteins, making the identification of virulence factors difficult. Gene expression analyses can be used to identify potentially important gene products for further study, based on the conditions under which they are expressed. To this end, the B. burgdorferi in vivo transcriptome of selected potential surface proteins was analyzed to identify promising targets for further study. Based on these analyses and other observations from the literature, the lipoproteins BbCRASP-2 and BBK07 were selected for further characterization. My hypothesis is that these proteins are important for B. burgdorferi virulence and persistence in the murine host. The surface exposure of each protein was assessed, as well as a detailed transcriptional profile of each gene. Using specific antibody-mediated interference and gene inactivation, I show that neither BbCRASP-2 nor BBK07 is essential for infectivity or pathogenesis in the murine model of Lyme disease. My results also indicate that BBK07 is a novel immunodominant antigen of B. burgdorferi that could be used as a serodiagnostic marker for human Lyme disease. Using a peptide library, the most immunodominant epitopes of BBK07 were identified, and shown to improve the diagnostic accuracy over that of the full-length recombinant BBK07. Finally, I show that BBK07-based diagnosis was sensitive even in the early stages of Lyme disease, and that the addition of BBK07 epitopes to current serodiagnostic assays could improve their sensitivity