Unified model for vortex-string network evolution

We describe and numerically test the velocity-dependent one-scale (VOS) string evolution model, a simple analytic approach describing a string network with the averaged correlation length and velocity. We show that it accurately reproduces the large-scale behaviour (in particular the scaling laws) of numerical simulations of both Goto-Nambu and field theory string networks. We explicitly demonstrate the relation between the high-energy physics approach and the damped and non-relativistic limits which are relevant for condensed matter physics. We also reproduce experimental results in this context and show that the vortex-string density is significantly reduced by loop production, an effect not included in the usual `coarse-grained' approach.Comment: 5 pages; v2: cosmetic changes, version to appear in PR

Interface free energies in p-spin glass models

The replica method has been used to calculate the interface free energy associated with the change from periodic to anti-periodic boundary conditions in finite-dimensional p-spin glass models in the phase which at mean-field level has one-step replica symmetry breaking (1RSB). In any finite dimension the interface free energy is exponentially small for a large system. This result implies that in finite dimensions, the 1RSB state does not exist, as it is destroyed by thermal excitation of arbitrarily large droplets. The implications of this for the theory of structural glasses are discussed.Comment: 4 page

Recognising Desire: A psychosocial approach to understanding education policy implementation and effect

It is argued that in order to understand the ways in which teachers experience their work - including the idiosyncratic ways in which they respond to and implement mandated education policy - it is necessary to take account both of sociological and of psychological issues. The paper draws on original research with practising and beginning teachers, and on theories of social and psychic induction, to illustrate the potential benefits of this bipartisan approach for both teachers and researchers. Recognising the significance of (but somewhat arbitrary distinction between) structure and agency in teachers’ practical and ideological positionings, it is suggested that teachers’ responses to local and central policy changes are governed by a mix of pragmatism, social determinism and often hidden desires. It is the often underacknowledged strength of desire that may tip teachers into accepting and implementing policies with which they are not ideologically comfortable

Entanglement entropy of random quantum critical points in one dimension

For quantum critical spin chains without disorder, it is known that the entanglement of a segment of N>>1 spins with the remainder is logarithmic in N with a prefactor fixed by the central charge of the associated conformal field theory. We show that for a class of strongly random quantum spin chains, the same logarithmic scaling holds for mean entanglement at criticality and defines a critical entropy equivalent to central charge in the pure case. This effective central charge is obtained for Heisenberg, XX, and quantum Ising chains using an analytic real-space renormalization group approach believed to be asymptotically exact. For these random chains, the effective universal central charge is characteristic of a universality class and is consistent with a c-theorem.Comment: 4 pages, 3 figure

Origin of the Growing Length Scale in M-p-Spin Glass Models

Two versions of the M-p-spin glass model have been studied with the Migdal-Kadanoff renormalization group approximation. The model with p=3 and M=3 has at mean-field level the ideal glass transition at the Kauzmann temperature and at lower temperatures still the Gardner transition to a state like that of an Ising spin glass in a field. The model with p=3 and M=2 has only the Gardner transition. In the dimensions studied, d=2,3 and 4, both models behave almost identically, indicating that the growing correlation length as the temperature is reduced in these models -- the analogue of the point-to-set length scale -- is not due to the mechanism postulated in the random first order transition theory of glasses, but is more like that expected on the analogy of glasses to the Ising spin glass in a field.Comment: 5 pages, 3 figures, revised versio

The Near-Infrared Extinction Law in Regions of High Av

We present a spectroscopic study of the shape of the dust-extinction law between 1.0 and 2.2um towards a set of nine ultracompact HII regions with Av > 15 mag. We find some evidence that the reddening curve may tend to flatten at higher extinctions, but just over half of the sample has extinction consistent with or close to the average for the interstellar medium. There is no evidence of extinction curves significantly steeper than the standard law, even where water ice is present. Comparing the results to the predictions of a simple extinction model, we suggest that a standard extinction law implies a robust upper limit to the grain-size distribution at around 0.1 - 0.3um. Flatter curves are most likely due to changes in this upper limit, although the effects of flattening due to unresolved clumpy extinction cannot be ruled out.Comment: 9 pages, 7 figure

Chern-Simons Number Diffusion and Hard Thermal Loops on the Lattice

We develop a discrete lattice implementation of the hard thermal loop effective action by the method of added auxiliary fields. We use the resulting model to measure the sphaleron rate (topological susceptibility) of Yang-Mills theory at weak coupling. Our results give parametric behavior in accord with the arguments of Arnold, Son, and Yaffe, and are in quantitative agreement with the results of Moore, Hu, and Muller.Comment: 43 pages, 6 figure

Sphaleron Transition Rate in Presence of Dynamical Fermions

We investigate the effect of dynamical fermions on the sphaleron transition rate at finite temperature for the Abelian Higgs model in one spatial dimension. The fermion degrees of freedom are included through bosonization. Using a numerical simulation, we find that massless fermions do not change the rate within the measurement accuracy. Surprisingly, the exponential dependence of the sphaleron energy on the Yukawa coupling is not borne out by the transition rate, which shows a very weak dependence on the fermion mass.Comment: 20 pages, 7 figures, LaTeX, psfi