Delusional Infestation:Perspectives from Scottish Dermatologists and a 10-year Case Series from a Single Centre

Perceptions of the clinical management of delusional infestation (DI) were compared with clinical outcomes in this 10-year case series from a single centre in Dundee, UK. An online questionnaire (survey-monkey, a TM brand of online survey available for free for basic use) was sent to Scottish Dermatologists to gauge their opinions and confidence in the management of DI. Also, a retrospective review of medical case notes of patients seen by dermatologists in one institution was undertaken and clinical outcomes were reported by patients’ general practitioners (GP). The survey showed that 61% of responding dermatologists encountered 1–5 cases of DI per year. Twenty-four percent respondees were ‘confident’ in managing patients with DI, 54% were ‘somewhat confident’. Forty-seven patients (62% female, 70% single) were seen over the 10 years; 43% brought a self-collected specimen to clinic, 68% of patients had a psychiatric comorbidity, 23% of patients had primary DI and 11/47 (23%) were seen by a psychiatrist. Clinical outcomes as rated by patients’ GPs were reasonable or good in 2/3 patients. A poor outcome was seen in 12 patients and associated with chronic pain in 50% (p< 0.01) and psychiatric comorbidity in 100% (p < 0.01). We conclude that good outcomes can be achieved in some patients with DI without psychiatric input and without psychoactive treatment

Paperclip at θ=π\theta=\pi

We study the ``paperclip'' model of boundary interaction with the topological angle $\theta$ equal to $\pi$. We propose exact expression for the disk partition function in terms of solutions of certain ordinary differential equation. Large distance asymptotic form of the partition function which follows from this proposal makes it possible to identify the infrared fixed point of the paperclip boundary flow at $\theta=\pi$.Comment: 22 pages, 4 figure

Vacuum defects without a vacuum

Topological defects can arise in symmetry breaking models where the scalar field potential $V(\phi)$ has no minima and is a monotonically decreasing function of $|\phi|$. The properties of such vacuumless defects are quite different from those of the ``usual'' strings and monopoles. In some models such defects can serve as seeds for structure formation, or produce an appreciable density of mini-black holes.Comment: 11 pages, REVTeX, 1 Postscript figure. Minor changes. Final version, to appear in Phys. Rev.

Integrable boundary interaction in 3D target space: the "pillow-brane" model

We propose a model of boundary interaction, with three-dimensional target space, and the boundary values of the field {\vec X}\in R^3 constrained to lay on a two-dimensional surface of the "pillow" shape. We argue that the model is integrable, and suggest that its exact solution is described in terms of certain linear ordinary differential equation.Comment: 28 pages, 4 figure

Spectral and Transport Properties of Quantum Wires with Bond Disorder

Systems with bond disorder are defined through lattice Hamiltonians that are of pure nearest neighbour hopping type, i.e. do not contain on-site contributions. Previous analyses based on the Dorokhov-Mello-Pereyra-Kumar (DMPK) transfer matrix technique have shown that both spectral and transport properties of quasi one-dimensional systems belonging to this category are highly unusual. Notably, regimes with absence of exponential Anderson localization are observed, the single particle density of states exhibits singular structure in the vicinity of the band centre, and the manifestation of these phenomena depends in an apparently topological manner on the even- or oddness of the channel number. In this paper we re-consider the problem from the complementary perspective of the non-linear sigma-model. Relying on the standard analogy between one-dimensional statistical field theories and zero-dimensional quantum mechanics, we will relate the problem to the behaviour of a quantum point particle subject to an Aharonov-Bohm flux. We will re-derive previous DMPK results, identify a new class of even/odd staggering phenomena and trace back the anomalous behaviour of the bond disordered system to a simple physical mechanism, viz. the flux periodicity of the quantum Aharonov-Bohm system. We will also touch upon connections to the low energy physics of other lattice systems, notably disordered chiral systems in 0 and 2 dimensions and antiferromagnetic spin chains.Comment: 55 pages, 2 figures include

From band insulator to Mott insulator in one dimension

We derive the phase diagram for the one-dimensional model of a ferroelectric perovskite recently introduced by Egami, Ishihara and Tachiki [Science, {\bf 261}, 1307 (1993)]. We show that the interplay between covalency, ionicity and strong correlations results in a spontaneously dimerized phase which separates the weak-coupling band insulator from the strong-coupling Mott insulator. The transition from the band insulator to the dimerized phase is identified as an Ising critical point. The charge gap vanishes at this single point with the optical conductivity diverging as $\sigma(\omega)\sim \omega^{-3/4}$. The spin excitations are gapless above the second transition to the Mott insulator phase.Comment: 4 pages LaTex (RevTex) and 1 postscript figure included by eps

Gravitational field of vacuumless defects

It has been recently shown that topological defects can arise in symmetry breaking models where the scalar field potential $V(\phi)$ has no minima and is a monotonically decreasing function of $|\phi|$. Here we study the gravitational fields produced by such vacuumless defects in the cases of both global and gauge symmetry breaking. We find that a global monopole has a strongly repulsive gravitational field, and its spacetime has an event horizon similar to that in de Sitter space. A gauge monopole spacetime is essentially that of a magnetically charged black hole. The gravitational field of a global string is repulsive and that of a gauge string is attractive at small distances and repulsive at large distances. Both gauge and global string spacetimes have singularities at a finite distance from the string core.Comment: 19 pages, REVTeX, 6 Postscript figure

Semiclassical transition in \phi^4 theory

We have shown an example of semiclassical transition in $\phi^{4}$ theory with positive coupling constant. This process can be described by the classical $O(4)$-invariant solution, considered on a contour in the complex time plane. The transition is technically analogous to the one-instanton transition in the electroweak model. It is suppressed by the factor $\exp(-2S_{0})$, where $S_{0}$ is Lipatov instanton action. This process describes a semiclassical transition between two coherent states with much smaller number of particles in the initial state than in the final state. Therefore, it could be relevant to the problem of calculation of amplitudes for multiparticle production in $\phi^4$-type models.Comment: 26 pages, JHU-TIPAC-930013, (correct 2 typos, some notations

Anderson-Yuval approach to the multichannel Kondo problem

We analyze the structure of the perturbation expansion of the general multichannel Kondo model with channel anisotropic exchange couplings and in the presence of an external magnetic field, generalizing to this case the Anderson-Yuval technique. For two channels, we are able to map the Kondo model onto a generalized resonant level model. Limiting cases in which the equivalent resonant level model is solvable are identified. The solution correctly captures the properties of the two channel Kondo model, and also allows an analytic description of the cross-over from the non Fermi liquid to the Fermi liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques

Theories of Low-Energy Quasi-Particle States in Disordered d-Wave Superconductors

The physics of low-energy quasi-particle excitations in disordered d-wave superconductors is a subject of ongoing intensive research. Over the last decade, a variety of conceptually and methodologically different approaches to the problem have been developed. Unfortunately, many of these theories contradict each other, and the current literature displays a lack of consensus on even the most basic physical observables. Adopting a symmetry-oriented approach, the present paper attempts to identify the origin of the disagreement between various previous approaches, and to develop a coherent theoretical description of the different low-energy regimes realized in weakly disordered d-wave superconductors. We show that, depending on the presence or absence of time-reversal invariance and the microscopic nature of the impurities, the system falls into one of four different symmetry classes. By employing a field-theoretical formalism, we derive effective descriptions of these universal regimes as descendants of a common parent field theory of Wess-Zumino-Novikov-Witten type. As well as describing the properties of each universal regime, we analyse a number of physically relevant crossover scenarios, and discuss reasons for the disagreement between previous results. We also touch upon other aspects of the phenomenology of the d-wave superconductor such as quasi-particle localization properties, the spin quantum Hall effect, and the quasi-particle physics of the disordered vortex lattice.Comment: 42 Pages, 8 postscript figures, published version with updated reference