Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics

In the quenched approximation, the gauge covariance properties of three vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy are analysed in three- and four- dimensional quantum electrodynamics. Based on the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the spectral representation used for the vertex in the gauge technique cannot support dynamical chiral symmetry breaking. A criterion for establishing whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson equation is presented and the Curtis and Pennington Ansatz is shown to satisfy this constraint. We obtain an analytic solution of the Schwinger-Dyson equation for quenched, massless three-dimensional quantum electrodynamics for arbitrary values of the gauge parameter in the absence of dynamical chiral symmetry breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE

Vector Positronium States in QED3

The homogeneous Bethe-Salpeter equation is solved in the quenched ladder approximation for the vector positronium states of 4-component quantum electrodynamics in 2 space and 1 time dimensions. Fermion propagator input is from a Rainbow approximation Dyson-Schwinger solution, with a broad range of fermion masses considered. This work is an extension of earlier work on the scalar spectrum of the same model. The non-relativistic limit is also considered via the large fermion mass limit. Classification of states via their transformation properties under discrete parity transformations allows analogies to be drawn with the meson spectrum of QCD.Comment: 24 pages, 2 encapsulated postscript figure

The analytic structure of heavy quark propagators

The renormalised quark Dyson-Schwinger equation is studied in the limit of the renormalised current heavy quark mass m_R --> infinity. We are particularly interested in the analytic pole structure of the heavy quark propagator in the complex momentum plane. Approximations in which the quark-gluon vertex is modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau gauge gluon propagator takes either a gaussian form or a gaussian form with an ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this paper has been considerably extended to include a formalism dealing with the renormalised heavy quark Dyson-Schwinger equation and uses a more realistic Ansatz for the gluon propagator

Gauge covariant fermion propagator in quenched, chirally-symmetric quantum electrodynamics

We discuss the chirally symmetric solution of the massless, quenched, Dyson-Schwinger equation for the fermion propagator in three and four dimensions. The solutions are manifestly gauge covariant. We consider a gauge covariance constraint on the fermion--gauge-boson vertex, which motivates a vertex Ansatz that both satisfies the Ward identity when the fermion self-mass is zero and ensures gauge covariance of the fermion propagator.Comment: 11 pages. REVTEX 3.0. ANL-PHY-7711-TH-9

Nonperturbative Vertices in Supersymmetric Quantum Electrodynamics

We derive the complete set of supersymmetric Ward identities involving only two- and three- point proper vertices in supersymmetric QED. We also present the most general form of the proper vertices consistent with both the supersymmetric and U(1) gauge Ward identities. These vertices are the supersymmetric equivalent of the non supersymmetric Ball-Chiu vertices.Comment: seventeen pages late

Improvement, dynamical fermions, and heavy quark screening in QCD_3

First results from simulations of improved actions for both gauge fields and staggered fermion fields in three dimensional QCD are presented. This work provides insight into some issues of relevance to lattice theories in four dimensions. In particular, the renormalization of the bare lattice coupling is dramatically reduced when the tree-level $O(a^2)$ improved action is used. Naik improvement of the staggered fermion action produces little reduction in scaling violations of the rho meson mass. String breaking in the heavy quark potential in the unquenched theory is also clearly resolved, using Wilson loops to bound the ground state energy.Comment: LATTICE98(improvement), 3 pages, 3 figures (psfig format

Patients with Diabetic Nephropathy in Established Renal Failure: Demographics, Survival and Biochemical Variables (Chapter 16)

Diabetic nephropathy is now the most common renal disease leading to renal replacement therapy in developed countries1,2,3,4. Within the UK, the number of DN patients accepted for RRT rose steadily in the 1990s5 especially in the African–Caribbean and South Asian populations3,4,5,6. This may be related to the increased prevalence of Type 2 diabetes in the general population, the ageing population and the liberalisation of attitudes to acceptance for RRT5,7. The overall rise has slowed in the last 4 years8 . DN patients starting RRT are likely to have more co-morbidity than other patients, in particular cardiovascular disease, and consequently worse survival on RRT9,10,11. In recent years there has been some reduction in the high mortality of such patients, so the prevalence of diabetic nephropathy patients on RRT (currently lower than the percentage of incident patients, see Chapter 3) might increase12,13. The National Service Frameworks for Diabetes14 and for Renal Services15 have highlighted the importance of the primary prevention of DN in diabetic patients by early detection and aggressive management of hypertension, glucose control and cardiovascular risk factors and of the timely referral (recommendation >1 yr before RRT) of those with progressive renal disease in order to plan for RRT. 251 There is a key policy drive to reduce health inequalities in England16. In the UK there is evidence that diabetic patients in more socially deprived areas have higher all cause mortality even after adjustment for smoking and blood pressure9 , and lower rates of attendance at GP and hospital clinics17. The UK Renal Registry 2003 Report highlighted the possible role of social deprivation in the context of DN. This chapter examines the characteristics of patients developing established renal failure from DN, their access to modalities of treatment and their survival on RRT relative to other incident patients. It also includes data on quality of care (HbA1c, cholesterol and blood pressure). These analyses were undertaken before individual patient data from the Scottish Registry became available and therefore only includes England and Wales

The Ethics and Impact of Digital Immortality

The concept of digital immortality has emerged over the past decade and is defined here as the continuation of an active or passive digital presence after death. Advances in knowledge management, machine to machine communication, data mining and artificial intelligence are now making a more active presence after death possible. This paper examines the research and literature around active digital immortality and explores the emotional, social, financial, and business impact of active digital immortality on relations, friends, colleagues and institutions. The issue of digital immortality also raises issues about the legal implications of a possible autonomous presence that reaches beyond mortal existence, and this will also be investigated. The final section of the paper questions whether digital immortality is really a concern and reflects on the assumptions about it in relation to neoliberal capitalism. It suggests that digital immortality may in fact merely be a clever ruse which in fact is likely to have little, if any legal impact despite media assumptions and hyperbole

QED in external fields, a functional point of view

A functional partial differential equation is set for the proper graphs generating functional of QED in external electromagnetic fields. This equation leads to the evolution of the proper graphs with the external field amplitude and the external field gauge dependence of the complete fermion propagator and vertex is derived non-perturbativally.Comment: 8 pages, published versio