Colour, copies and confinement

In this paper we construct a wide class of Gribov copies in Coulomb gauge SU(2) gauge theory. Infinitesimal copies are studied in some detail and their non-perturbative nature is made manifest. As an application it is shown that the copies prevent a non-perturbative definition of colour charge.Comment: 25 pages, 10 figures. Minor changes, two references added. Published versio

Non-verbal communication in meetings of psychiatrists and patients with schizophrenia

Objective Recent evidence found that patients with schizophrenia display non‐verbal behaviour designed to avoid social engagement during the opening moments of their meetings with psychiatrists. This study aimed to replicate, and build on, this finding, assessing the non‐verbal behaviour of patients and psychiatrists during meetings, exploring changes over time and its association with patients' symptoms and the quality of the therapeutic relationship. Method 40‐videotaped routine out‐patient consultations, involving patients with schizophrenia, were analysed. Non‐verbal behaviour of patients and psychiatrists was assessed during three fixed, 2‐min intervals using a modified Ethological Coding System for Interviews. Symptoms, satisfaction with communication and the quality of the therapeutic relationship were also measured. Results Over time, patients' non‐verbal behaviour remained stable, whilst psychiatrists' flight behaviour decreased. Patients formed two groups based on their non‐verbal profiles, one group (n = 25) displaying pro‐social behaviour, inviting interaction and a second (n = 15) displaying flight behaviour, avoiding interaction. Psychiatrists interacting with pro‐social patients displayed more pro‐social behaviours (P < 0.001). Patients' pro‐social profile was associated reduced symptom severity (P < 0.05), greater satisfaction with communication (P < 0.001) and positive therapeutic relationships (P < 0.05). Conclusion Patients' non‐verbal behaviour during routine psychiatric consultations remains unchanged, and is linked to both their psychiatrist's non‐verbal behaviour and the quality of the therapeutic relationship

Burglary project

This report outlines the process and findings from an innovative project for students. This work was part of the curriculum and involved students working with West Yorkshire Police as part of the safer Leeds project in designing and making a film for students n crime prevention and personal safety in Leed

The Nielsen Identities for the Two-Point Functions of QED and QCD

We consider the Nielsen identities for the two-point functions of full QCD and QED in the class of Lorentz gauges. For pedagogical reasons the identities are first derived in QED to demonstrate the gauge independence of the photon self-energy, and of the electron mass shell. In QCD we derive the general identity and hence the identities for the quark, gluon and ghost propagators. The explicit contributions to the gluon and ghost identities are calculated to one-loop order, and then we show that the quark identity requires that in on-shell schemes the quark mass renormalisation must be gauge independent. Furthermore, we obtain formal solutions for the gluon self-energy and ghost propagator in terms of the gauge dependence of other, independent Green functions.Comment: 25 pages, plain TeX, 4 figures available upon request, MZ-TH/94-0

Collinearity, convergence and cancelling infrared divergences

The Lee-Nauenberg theorem is a fundamental quantum mechanical result which provides the standard theoretical response to the problem of collinear and infrared divergences. Its argument, that the divergences due to massless charged particles can be removed by summing over degenerate states, has been successfully applied to systems with final state degeneracies such as LEP processes. If there are massless particles in both the initial and final states, as will be the case at the LHC, the theorem requires the incorporation of disconnected diagrams which produce connected interference effects at the level of the cross-section. However, this aspect of the theory has never been fully tested in the calculation of a cross-section. We show through explicit examples that in such cases the theorem introduces a divergent series of diagrams and hence fails to cancel the infrared divergences. It is also demonstrated that the widespread practice of treating soft infrared divergences by the Bloch-Nordsieck method and handling collinear divergences by the Lee-Nauenberg method is not consistent in such cases.Comment: 29 pages, 17 figure

AIDS prevention in South Africa: A perspective from other African countries

No Abstrac

Infra-Red Finite Charge Propagation

The Coulomb gauge has a long history and many uses. It is especially useful in bound state applications. An important feature of this gauge is that the matter fields have an infra-red finite propagator in an on-shell renormalisation scheme. This is, however, only the case if the renormalisation point is chosen to be the static point on the mass shell, p = (m, 0, 0, 0). In this letter we show how to extend this key property of the Coulomb gauge to an arbitrary relativistic renormalisation point. This is achieved through the introduction of a new class of gauges of which the Coulomb gauge is a limiting case. A physical explanation for this result is given.Comment: 8 pages, plain TeX, to appear in Modern Physics Letters

Asymptotic Dynamics in Quantum Field Theory

A crucial element of scattering theory and the LSZ reduction formula is the assumption that the coupling vanishes at large times. This is known not to hold for the theories of the Standard Model and in general such asymptotic dynamics is not well understood. We give a description of asymptotic dynamics in field theories which incorporates the important features of weak convergence and physical boundary conditions. Applications to theories with three and four point interactions are presented and the results are shown to be completely consistent with the results of perturbation theory.Comment: 18 pages, 3 figure

Wilson Loop and the Treatment of Axial Gauge Poles

We consider the question of gauge invariance of the Wilson loop in the light of a new treatment of axial gauge propagator proposed recently based on a finite field-dependent BRS (FFBRS) transformation. We remark that as under the FFBRS transformation the vacuum expectation value of a gauge invariant observable remains unchanged, our prescription automatically satisfies the Wilson loop criterion. Further, we give an argument for {\it direct} verification of the invariance of Wilson loop to O(g^4) using the earlier work by Cheng and Tsai. We also note that our prescription preserves the thermal Wilson loop to O(g^2).Comment: 8 pages, LaTex; some typos related to equation (18) correcte