2,874 research outputs found
Quantum rotor description of the Mott-insulator transition in the Bose-Hubbard model
We present the novel approach to the Bose-Hubbard model using the
quantum rotor description. The effective action formalism
allows us to formulate a problem in the phase only action and obtain an
analytical formulas for the critical lines. We show that the nontrivial
phase field configurations have an impact on the phase
diagrams. The topological character of the quantum field is governed by terms
of the integer charges - winding numbers. The comparison presented results to
recently obtained quantum Monte Carlo numerical calculations suggests that the
competition between quantum effects in strongly interacting boson systems is
correctly captured by our model.Comment: accepted to PR
Emotional experiences beyond the classroom: Interactions with the social world
Research into the emotional experiences of language learners and their impact upon the language-learning process remains relatively undernourished within second language education. The research available focuses primarily on emotions experienced within the classroom, rather than in the daily lives of learners within various social contexts. This article contends that the focus placed upon emotions within the relatively structured environment of the formal classroom is problematic, particularly within an ESL environment, as the target language is more frequently experienced beyond the classroom. Drawing on data collected within Australia, the study explored the emotional experiences of a small cohort of eight university-level ESL learners experienced within their various social interactions beyond the classroom with a specific focus on the emotions of hope, enjoyment and frustration. Semi-structured interviews revealed that their emotional experiences beyond the classroom were particularly intense in comparison to emotional experiences within the formal language-learning classroom
Power-law tails from multiplicative noise
We show that the well-known Langevin equation, modeling the Brownian motion
and leading to a Gaussian stationary distribution of the corresponding
Fokker-Planck equation, is changed by the smallest multiplicative noise. This
leads to a power-law tail of the distribution at large enough momenta. At
finite ratio of the correlation strength for the multiplicative and additive
noise the stationary energy distribution becomes exactly the Tsallis
distribution.Comment: 4 pages, LaTeX, revtex4 style, 2 figure
The role of Causality in Tunable Fermi Gas Condensates
We develop a new formalism for the description of the condensates of cold
Fermi atoms whose speed of sound can be tuned with the aid of a narrow Feshbach
resonance. We use this to look for spontaneous phonon creation that mimics
spontaneous particle creation in curved space-time in
Friedmann-Robertson-Walker and other model universes.Comment: 9 pages, 2 figures. In v.3 the formalism is different from the
existing arXiv versions, but the final results are unchanged. Title changed,
one author added. The article will be published in the special edition of
Journal of Physics: Condensed Matter on "Condensed matter analogues of
cosmology
Classical Physics and Quantum Loops
The standard picture of the loop expansion associates a factor of h-bar with
each loop, suggesting that the tree diagrams are to be associated with
classical physics, while loop effects are quantum mechanical in nature. We
discuss examples wherein classical effects arise from loop contributions and
display the relationship between the classical terms and the long range effects
of massless particles.Comment: 15 pages, 3 figure
Interactions In Space For Archaeological Models
In this article we examine a variety of quantitative models for describing
archaeological networks, with particular emphasis on the maritime networks of
the Aegean Middle Bronze Age. In particular, we discriminate between those
gravitational networks that are most likely (maximum entropy) and most
efficient (best cost/benefit outcomes).Comment: 21 pages, 6 figures, 2 tables. Contribution to special issue of
Advances in Complex Systems from the conference `Cultural Evolution in
Spatially Structured Populations', UCL, London, September 2010. To appear in
Advances in Complex System
Vortex Production in Non-Relativistic and Relativistic Media
We examine string (vortex) formation at a quench for a weakly-coupled global
U(1) theory when the excitation spectrum is non-relativistic. It is so similar
to vortex production in the corresponding relativistic plasma as to reinforce
arguments for the similarity of vortex production in the early universe and in
low-temperature many-body physics.Comment: 20 pages, RevTeX and epsf, 1 postscript figure. Resubmitted because
archive (not a bulletin board) ate the figures file first time round.
Available through anonymous ftp as LaTeX from
ftp://euclid.tp.ph.ic.ac.uk/papers/94-5_53.tex or as LaTeX or postscript at
http://euclid.tp.ph.ic.ac.uk/Papers/index.htm
Optimized perturbation theory for charged scalar fields at finite temperature and in an external magnetic field
Symmetry restoration in a theory of a self-interacting charged scalar field
at finite temperature and in the presence of an external magnetic field is
examined. The effective potential is evaluated nonperturbatively in the context
of the optimized perturbation theory method. It is explicitly shown that in all
ranges of the magnetic field, from weak to large fields, the phase transition
is second order and that the critical temperature increases with the magnetic
field. In addition, we present an efficient way to deal with the sum over the
Landau levels, which is of interest especially in the case of working with weak
magnetic fields.Comment: 18 pages, 7 eps figures. References added and some small improvements
to the tex
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