14,905 research outputs found
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 complex Langevin dynamics evade the sign problem?
I answer the question in the title for the relativistic Bose gas at finite
chemical potential using numerical lattice simulations, complemented with
analytical understanding.Comment: 7 pages, talk given at the XXVII International Symposium on Lattice
Field Theory, July 26-31 2009, Peking University, Beijing, Chin
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
'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
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
Nonequilibrium Fields: Exact and Truncated Dynamics
The nonperturbative real-time evolution of quantum fields out of equilibrium
is often solved using a mean-field or Hartree approximation or by applying
effective action methods. In order to investigate the validity of these
truncations, we implement similar methods in classical scalar field theory and
compare the approximate dynamics with the full nonlinear evolution. Numerical
results are shown for the early-time behaviour, the role of approximate fixed
points, and thermalization.Comment: 5 pages, 6 eps figures, talk presented at Strong and Electroweak
Matter (SEWM2000), Marseille, France, 14-17 June, 200
Lefschetz thimbles and stochastic quantisation: Complex actions in the complex plane
Lattice field theories with a complex action can be studied numerically by
allowing a complexified configuration space to be explored. Here we compare the
recently introduced formulation on a Lefschetz thimble with the result from
stochastic quantisation (or complex Langevin dynamics) in the case of a simple
model and contrast the distributions being sampled. We also study the role of
the residual phase on the Lefschetz thimble.Comment: 13 pages, 7 figure
Renormalizability of hot classical field theory
I discuss the possibility of using classical field theory to approximate hot,
real-time quantum field theory. I calculate, in a scalar theory, the classical
two point and four point function in perturbation theory. The counterterms
needed to make the classical correlation functions finite are dictated by the
superrenormalizability of the static theory. The classical expressions
approximate the quantum ones, when the classical parameters are chosen
according to the dimensional reduction matching rules. I end with an outlook to
gauge theories.Comment: 5 pages, 1 eps figure. To appear in the Proceedings of Strong and
Electroweak Matter '97, Eger, Hungary, 21-25 May 199
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