27,410 research outputs found
Thermal Abundances of Heavy Particles
Matsumoto and Yoshimura [hep-ph/9910393] have argued that there are loop
corrections to the number density of heavy particles (in thermal equilibrium
with a gas of light particles) that are not Boltzmann suppressed by a factor of
e^(-M/T) at temperatures T well below the mass M of the heavy particle. We
argue, however, that their definition of the number density does not correspond
to a quantity that could be measured in a realistic experiment. We consider a
model where the heavy particles carry a conserved U(1) charge, and the light
particles do not. The fluctuations of the net charge in a given volume then
provide a measure of the total number of heavy particles in that same volume.
We show that these charge fluctuations are Boltzmann suppressed (to all orders
in perturbation theory). Therefore, we argue, the number density of heavy
particles is also Boltzmann suppressed.Comment: 9 pages, 1 figure; minor improvements in revised versio
The role of social networks in understanding language maintenance and shift in post-colonial multilingual communities — The case of the Republic of Palau in the Western Pacific
Conservative and innovative behaviour by female speakers in a multilingual Micronesian society
Cuntz-Pimsner C*-algebras associated with subshifts
By using C*-correspondences and Cuntz-Pimsner algebras, we associate to every
subshift (also called a shift space) a C*-algebra , which is a
generalization of the Cuntz-Krieger algebras. We show that is the
universal C*-algebra generated by partial isometries satisfying relations given
by . We also show that is a one-sided conjugacy invariant of .Comment: 28 pages. This is a slightly updated version of a preprint from 2004.
Submitted for publication. In version 2 the Introduction has been changed,
two remarks (Remark 7.6 and 7.7) have been added and the list of references
has been update
Complex-space singularities of 2D Euler flow in Lagrangian coordinates
We show that, for two-dimensional space-periodic incompressible flow, the
solution can be evaluated numerically in Lagrangian coordinates with the same
accuracy achieved in standard Eulerian spectral methods. This allows the
determination of complex-space Lagrangian singularities. Lagrangian
singularities are found to be closer to the real domain than Eulerian
singularities and seem to correspond to fluid particles which escape to
(complex) infinity by the current time. Various mathematical conjectures
regarding Eulerian/Lagrangian singularities are presented.Comment: 5 pages, 2 figures, submitted to Physica
Singularities of Euler flow? Not out of the blue!
Does three-dimensional incompressible Euler flow with smooth initial
conditions develop a singularity with infinite vorticity after a finite time?
This blowup problem is still open. After briefly reviewing what is known and
pointing out some of the difficulties, we propose to tackle this issue for the
class of flows having analytic initial data for which hypothetical real
singularities are preceded by singularities at complex locations. We present
some results concerning the nature of complex space singularities in two
dimensions and propose a new strategy for the numerical investigation of
blowup.(A version of the paper with higher-quality figures is available at
http://www.obs-nice.fr/etc7/complex.pdf)Comment: RevTeX4, 10 pages, 9 figures. J.Stat.Phys. in press (updated version
Bose-Einstein condensation of magnons in TlCuCl
A quantitative study of the field-induced magnetic ordering in TlCuCl in
terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is
shown that the hitherto proposed simple BEC scenario is in quantitative and
qualitative disagreement with experiment. It is further shown that even very
small Dzyaloshinsky-Moriya interactions or a staggered tensor component of
a certain type can change the BEC picture qualitatively. Such terms lead to a
nonzero condensate density for all temperatures and a gapped quasiparticle
spectrum. Including this type of interaction allows us to obtain good agreement
with experimental data.Comment: 2 pages, 2 figures, submitted to SCES'0
Why Two Renormalization Groups are Better than One
The advantages of using more than one renormalization group (RG) in problems
with more than one important length scale are discussed. It is shown that: i)
using different RG's can lead to complementary information, i.e. what is very
difficult to calculate with an RG based on one flow parameter may be much more
accessible using another; ii) using more than one RG requires less physical
input in order to describe via RG methods the theory as a function of its
parameters; iii) using more than one RG allows one to solve problems with more
than one diverging length scale. The above points are illustrated concretely in
the context of both particle physics and statistical physics using the
techniques of environmentally friendly renormalization. Specifically, finite
temperature theory, an Ising-type system in a film geometry, an
Ising-type system in a transverse magnetic field, the QCD coupling constant at
finite temperature and the crossover between bulk and surface critical
behaviour in a semi-infinite geometry are considered.Comment: 17 pages LaTex; to be published in the Proceedings of RG '96, Dubn
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