Scaling in a SU(2)/Z_3 model of cosmic superstring networks

Motivated by recent developments in superstring theory in the cosmological context, we examine a field theory which contains string networks with 3-way junctions. We perform numerical simulations of this model, identify the length scales of the network that forms, and provide evidence that the length scales tend towards a scaling regime, growing in proportion to time. We infer that the presence of junctions does not in itself cause a superstring network to dominate the energy density of the early Universe.Comment: 12pp, 3 fig

A model realisation of the Jaffe-Wilczek correlation for pentaquarks

We discuss a realisation of the pentaquark structure proposed by Jaffe and Wilczek within a simple quark model with colour-spin contact interactions and coloured harmonic confinement, which accurately describes the $\Delta-N$ splitting. In this model spatially compact diquarks are formed in the pentaquark but no such compact object exists in the nucleon. The colour-spin attraction brings the Jaffe-Wilczek-like state down to a low mass, compatible with the experimental observation and below that of the naive ground state with all $S$-waves. We find, however, that although these trends are maintained, the extreme effects observed do not survive the required ``smearing'' of the delta function contact interaction. We also demonstrate the weakness of the ``schematic'' approximation when applied to a system containing a $P$-wave. An estimate of the anti-charmed pentaquark mass is made which is in line with the Jaffe-Wilczek prediction and significantly less than the value reported by the H1 collaboration.Comment: 10 pages, uses psfra

Processes maintaining tropopause sharpness in numerical models

Recent work has shown that the sharpness of the extratropical tropopause declines with lead 15 time in numerical weather prediction models, indicating an imbalance between processes act16 ing to sharpen and smooth the tropopause. In this study the systematic effects of processes 17 contributing to the tropopause sharpness are investigated using daily initialised forecasts 18 run with the Met Office Unified Model over a three-month winter period. Artificial tracers, 19 each forced by the potential vorticity tendency due to a different model process, are used 20 to separate the effects of such processes. The advection scheme is shown to result in an ex21 ponential decay of tropopause sharpness towards a finite value at short lead times with a 22 timescale of 20-24 hours. The systematic effect of non-conservative processes is to sharpen 23 the tropopause, consistent with previous case studies. The decay of tropopause sharpness 24 due to the advection scheme is stronger than the sharpening effect of non-conservative pro25 cesses leading to a systematic decline in tropopause sharpness with forecast lead time. The 26 systematic forecast errors in tropopause-level potential vorticity are comparable to the inte27 grated tendencies of the parametrized physical processes suggesting that the systematic error 28 in tropopause sharpness could be significantly reduced through realistic adjustments to the 29 model parametrization schemes

Assessment of the benefits of user involvement in health research from the Warwick Diabetes Care Research User Group : a qualitative case study

Objective  To assess the benefits of involving health-care users in diabetes research. Design and participants  For this qualitative case study, semi-structured interviews were conducted with researchers who had worked extensively with the group. During regular meetings of the Research User Group, members discussed their views of the group's effectiveness as part of the meeting's agenda. Interviews and discussions were transcribed, coded using N-Vivo software and analysed using constant comparative methods. Results  Involvement of users in research was generally seen as contributing to effective and meaningful research. However, the group should not be considered to be representative of the patient population or participants of future trials. An important contributor to the group's success was its longstanding nature, enabling users to gain more insight into research and form constructive working relationships with researchers. The user-led nature of the group asserted itself, especially, in the language used during group meetings. A partial shift of power from researchers to users was generally acknowledged. Users' main contribution was their practical expertise in living with diabetes, but their involvement also helped researchers to remain connected to the `real world' in which research would be applied. While the group's work fulfilled established principles of consumer involvement in research, important contributions relying on personal interaction between users and researchers were hard to evaluate by process measures alone. Conclusions  We demonstrated the feasibility, acceptability and effectiveness of this longstanding, experienced, lay-led research advisory group. Its impact on research stems from the continuing interaction between researchers and users, and the general ethos of learning from each other in an on-going process. Both process measures and qualitative interviews with stakeholders are needed to evaluate the contributions of service users to health research

Scaling solutions and geodesics in moduli space

In this paper we consider cosmological scaling solutions in general relativity coupled to scalar fields with a non-trivial moduli space metric. We discover that the scaling property of the cosmology is synonymous with the scalar fields tracing out a particular class of geodesics in moduli space - those which are constructed as integral curves of the gradient of the log of the potential. Given a generic scalar potential we explicitly construct a moduli metric that allows scaling solutions, and we show the converse - how one can construct a potential that allows scaling once the moduli metric is known.Comment: 10 pages, 3 figure

Gravitating Fluxbranes

We consider the effect that gravity has when one tries to set up a constant background form field. We find that in analogy with the Melvin solution, where magnetic field lines self-gravitate to form a flux-tube, the self-gravity of the form field creates fluxbranes. Several exact solutions are found corresponding to different transverse spaces and world-volumes, a dilaton coupling is also considered.Comment: 14 pages, 5 figure

Inflaton Fragmentation and Oscillon Formation in Three Dimensions

Analytical arguments suggest that a large class of scalar field potentials permit the existence of oscillons -- pseudo-stable, non-topological solitons -- in three spatial dimensions. In this paper we numerically explore oscillon solutions in three dimensions. We confirm the existence of these field configurations as solutions to the Klein-Gorden equation in an expanding background, and verify the predictions of Amin and Shirokoff for the characteristics of individual oscillons for their model. Further, we demonstrate that significant numbers of oscillons can be generated via fragmentation of the inflaton condensate, consistent with the analysis of Amin. These emergent oscillons can easily dominate the post-inflationary universe. Finally, both analytic and numerical results suggest that oscillons are stable on timescales longer than the post-inflationary Hubble time. Consequently, the post-inflationary universe can contain an effective matter-dominated phase, during which it is dominated by localized concentrations of scalar field matter.Comment: See http://easther.physics.yale.edu/downloads.html for numerical codes. Visualizations available at http://www.mit.edu/~mamin/oscillons.html and http://easther.physics.yale.edu/fields.html V2 Minor fixes to reference lis

Adiabatic and isocurvature perturbation projections in multi-field inflation

Current data are in good agreement with the predictions of single field inflation. However, the hemispherical asymmetry seen in the cosmic microwave background data, may hint at a potential problem. Generalizing to multi-field models may provide one possible explanation. A useful way of modeling perturbations in multi-field inflation is to investigate the projection of the perturbation along and perpendicular to the background fields' trajectory. These correspond to the adiabatic and isocurvature perturbations. However, it is important to note that in general there are no corresponding adiabatic and isocurvature fields. The purpose of this article is to highlight the distinction between a field redefinition and a perturbation projection. We provide a detailed derivation of the evolution of the isocurvature perturbation to show that no assumption of an adiabatic or isocurvature field is needed. We also show how this evolution equation is consistent with the field covariant evolution equations for the isocurvature perturbation in the flat field space limit

Fluxbranes from p-branes

It is shown how magnetic fluxbrane, Fp-brane, solutions are related to electric black p-branes by analytic continuation. Viewing the transverse space of branes as a warped cone, one finds that the cone base of the p-brane becomes the world-volume of the F(D-p-3)-brane and the world volume of the p-brane becomes the cone base of the F(D-p-3)-brane. An explicit example of the correspondence is given for a 2-brane and F6-brane of 11D supergravity.Comment: 7 pages, no figure

Coleman meets Schwinger

It is well known that spherical D-branes are nucleated in the presence of an external RR electric field. Using the description of D-branes as solitons of the tachyon field on non-BPS D-branes, we show that the brane nucleation process can be seen as the decay of the tachyon false vacuum. This process can describe the decay of flux-branes in string theory or the decay of quintessence potentials arising in flux compactifications.Comment: 5 pages, 2 figure