205 research outputs found
Disoriented chiral condensate in (1+1) Lorentz-invariant geometry
We consider isospin correlations of pions produced in a relativistic nuclear
collision, using an effective theory of the chiral order parameter. Our theory
has (1+1) Lorentz invariance as appropriate for the central rapidity region. We
argue that in certain regions of space correlations of the chiral order
parameter are described by the fixed point of the (1+1) WZNW model. The
corresponding anomalous dimension determines scaling of the probability to
observe a correlated cluster of pions with the size of this cluster in
rapidity. Though the maximal size of clusters for which this scaling is
applicable is cut off by pion mass, such clusters can still include
sufficiently many particles to make the scaling observable.Comment: 9 pages, LATEX, UCLA/93/TEP/1
Quasiparticle scattering by quantum phase slips in one-dimensional superfluids
Quantum phase slips (QPS) in narrow superfluid channels generate momentum by
unwinding the supercurrent. In a uniform Bose gas, this momentum needs to be
absorbed by quasiparticles (phonons). We show that this requirement results in
an additional exponential suppression of the QPS rate (compared to the rate of
QPS induced by a sharply localized perturbation). In BCS-paired fluids,
momentum can be transferred to fermionic quasiparticles, and we find an
interesting interplay between quasiparticle scattering on QPS and on disorder.Comment: 4 pages, revtex, no figures; to be published in Phys. Rev. Letter
Melting of the Higgs Vacuum: Conserved Numbers at High Temperature
We discuss the computation of the grand canonical partition sum describing hot matter in systems with the Higgs mechanism in the presence of non-zero conserved global charges. We formulate a set of simple rules for that computation in the high-temperature approximation in the limit of small chemical potentials. As an illustration of the use of these rules, we calculate the leading term in the free energy of the standard model as a function of baryon number B. We show that this quantity depends continuously on the Higgs expectation value , with a crossover at where Debye screening overtakes the Higgs mechanism---the Higgs vacuum ``melts". A number of confusions that exist in the literature regarding the B dependence of the free energy is clarified
A remark on sphaleron erasure of baryon asymmetry
We complete an existing result for how the baryon asymmetry left over after a
period of full thermal equilibrium depends on different lepton asymmetries.Comment: 5 pages; small clarifications and a reference added; to appear in PR
The current of fermions scattered off a bubble wall
Proceeding from WKB quantization conditions, we derive a semiclassical
expression for the current of fermions scattered off a propagating bubble wall
in the presence of longitudinal gauge field. It agrees with the expression used
by Nasser and Turok in semiclassical analysis of instability of electroweak
bubble walls with respect to longitudinal condensation. We discuss the
resulting dispersion relation for longitudinal field and show that light
species are important for the analysis of stability, because of their large
contribution to plasma frequency.Comment: 7 pages, latex, no figures; misprint in eq.(12) correcte
Magnus Force in Discrete and Continuous Two-Dimensional Superfluids
Motion of vortices in two-dimensional superfluids in the classical limit is
studied by solving the Gross-Pitaevskii equation numerically on a uniform
lattice. We find that, in the presence of a superflow directed along one of the
main lattice periods, vortices move with the superflow on fine lattices but
perpendicular to it on coarse ones. We interpret this result as a transition
from the full Magnus force in the Galilean-invariant limit to vanishing
effective Magnus force in a discrete system, in agreement with the existing
experiments on vortex motion in Josephson junction arrays.Comment: 6 pages, 7 figures; published in Phys. Rev.
Quantum Dew
We consider phase separation in nonequilibrium Bose gas with an attractive
interaction between the particles. Using numerical integrations on a lattice,
we show that the system evolves into a state that contains drops of
Bose-Einstein condensate suspended in uncondensed gas. When the initial gas is
sufficiently rarefied, the rate of formation of this quantum dew scales with
the initial density as expected for a process governed by two-particle
collisions.Comment: 4 pages, revtex, 5 figure
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