Spectral function at high temperature

For a weakly coupled quantum field at high temperature the classical approximation offers a possibility to gain insight into nonperturbative real-time dynamics. I use this to present a nonperturbative approach to the computation of spectral functions in real time. Results are shown for a scalar field in 2+1 dimensions.Comment: Lattice2001(hightemp), 3 pages with 3 eps figure

The Classical Approximation for Real-Time Scalar Field Theory at Finite Temperature

The use of classical thermal field to approximate real-time quantum thermal field theory is discussed. For a \lambda\phi^4 theory, it is shown that the classical Rayleigh-Jeans divergence can be canceled with the appropriate counterterms, and a comparison is made between the classical and quantum perturbative expansion. It is explained why Hard Thermal Loops prevent the same method to work for gauge theories.Comment: 5 pages, 2 eps figures, talk presented at the 5th International Workshop on Thermal Field Theories and Their Applications, Regensburg, Germany, August 10-14, 199

Can stochastic quantization evade the sign problem? -- the relativistic Bose gas at finite chemical potential

A nonperturbative study of field theories with a complex action, such as QCD at finite baryon density, is difficult due to the sign problem. We show that the relativistic Bose gas at finite chemical potential has a sign and `Silver Blaze' problem, similar to QCD. We then apply stochastic quantization and complex Langevin dynamics to study this theory with nonperturbative lattice simulations. Independence of chemical potential at small and a transition to a condensed phase at large chemical potential are found. Lattices of size N^4, with N=4,6,8,10, are used. We show that the sign problem is severe, however, we find that it has no negative effect using this approach. This improves the prospects of applying stochastic quantization to QCD at nonzero density.Comment: 4 pages, 4 eps figures, v2: minor changes, outlook expanded, references added, to appear in PR

Complex Langevin dynamics and other approaches at finite chemical potential

I review the presence of the sign problem in lattice QCD at nonzero baryon density and its relation with the overlap and Silver Blaze problems. I then discuss progress in some cases where the sign problem can be handled, either because the sign problem is absent or because it is milder than in full QCD. Some time is spent on effective three-dimensional models, which can be treated with a variety of methods. I conclude with a discussion of the applicability of complex Langevin dynamics at nonzero density.Comment: 22 pages, several figures, invited plenary talk at Lattice 2012, Cairns, Australia, June 24-29 2012; ref [36] properly correcte

Transport and spectral functions in high-temperature QCD

The current status of transport coefficients in relativistic field theories at high temperature is reviewed. I contrast weak coupling results obtained using kinetic theory/diagrammatic techniques with strong coupling results obtained using gauge/gravity duality, and describe the recent developments in extracting transport coefficients and spectral functions from lattice QCD simulations. The fate of quarkonium at high temperature as seen from the lattice is briefly mentioned as well.Comment: 15 pages, 9 eps figures, plenary talk at Lattice 2007, Regensburg, German

'Grammatici certant. Review article of 'The Cambridge Grammar of the English Language'(2002) by Rodney Huddleston and Geoffrey Pullum

The first large-scale modern grammars of English were Quirk et al.'s A grammar of contemporary English (1972) and A comprehensive grammar of the English language (1985). It has taken 18 years for a major competitor to be published. Many linguists, especially those whose main focus is English, will have looked forward to the publication of the present book. The Cambridge grammar of the English language (henceforth CaGEL) is first and foremost the brainchild of Rodney Huddleston, whose 1984 Introduction to the grammar of English had already established itself as an important text. He was joined by Geoffrey Pullum and the other authors listed above at various points in time

Meson spectral functions with chirally symmetric lattice fermions

In order to enhance our understanding of spectral functions in lattice QCD obtained with the help of the Maximum Entropy Method, we study meson spectral functions for lattice fermions with chiral symmetry. In particular we analyse lattice artefacts for standard overlap, overlap hypercube and domain wall fermions in the free field limit. We also present first results for pseudoscalar spectral functions in dynamical QCD with 2+1 flavours of domain wall fermions, using data generated by the UKQCD and RBC collaborations on QCDOC machines.Comment: 25 pages, two sentences added; to appear in JHE

Calculation of free baryon spectral densities at finite temperature

Following a recent lattice study of nucleon parity doubling at finite temperature from the computation of the two-point nucleon correlators, we study the spectral functions of free nucleons at finite temperature. Spectral densities in the continuum are presented along with a comparison to (free) results on the lattice. Particular attention is given to lattice artefacts at higher energies.Comment: 7 pages, 6 figures. Talk presented at the 33rd International Symposium on Lattice Field Theory, 14 -18 July 2015, Kobe International Conference Center, Kobe, Japa

Modelling habitat preference and estimating the spatial distribution of Australian Sea Lions (Neophoca cinerea); "A first exploration "

Managing the Australian sea lion (Neophoca cinerea) population and mitigating its interactions with commercial fisheries, requires an understanding of their spatial distribution and habitat preference at sea. Numerous wildlife telemetry devices have been attached to individual seals from different colonies, providing a detailed insight into there movement and activities. However, as data are only available from some individuals from 16 of 40 colonies in South Australia, these data represents only a small proportion of the population. Moreover, some colonies are poorly represented. To estimate the spatial distribution of the entire South Australian population, one can first investigate why individuals visit certain places and use this information to predict the spatial distribution for other regions lacking data. In this study we fit Generalized Additive Mixed Models (GAMMs) to wildlife telemetry data collected from adult female Australian sea lions to investigate the species’ habitat preference for the variables distance to the colony, depth and slope. The results show that in general they have a higher preference for shallow areas, places close to the colony and a steep slope, but they also display large individual variability. Preference for these variables does not seem to differ between individuals of different sizes. In some of the most western colonies, some individuals seem to spend more time further away from the colony, but apart from this, there is no apparent effect of the longitudinal capture position on preference. The predicted spatial distribution is largely driven by the distance from the departure colony and the actual distribution of individuals among the different colonies. Although depth and slope does seem to effect their distribution to some extent, the most important variables that explain fine-scale foraging activities at-sea are probably missing. Future studies using GPS transmitters attached to animals, that yield high resolution locations and more detailed environmental data, in combination with the analytical technique presented here, should provide more insight there foraging decisions. This should eventually also improve the spatial prediction of the population as a whole