12,430 research outputs found
Dense loops, supersymmetry, and Goldstone phases in two dimensions
Loop models in two dimensions can be related to O(N) models. The
low-temperature dense-loops phase of such a model, or of its reformulation
using a supergroup as symmetry, can have a Goldstone broken-symmetry phase for
N<2. We argue that this phase is generic for -2< N <2 when crossings of loops
are allowed, and distinct from the model of non-crossing dense loops first
studied by Nienhuis [Phys. Rev. Lett. 49, 1062 (1982)]. Our arguments are
supported by our numerical results, and by a lattice model solved exactly by
Martins et al. [Phys. Rev. Lett. 81, 504 (1998)].Comment: RevTeX, 5 pages, 3 postscript figure
The mass of dwarf spheroidal galaxies and the missing satellite problem
We present the results from a suite of N-body simulations of the tidal
stripping of two-component dwarf galaxies comprising some stars and dark
matter. We show that recent kinematic data from the local group dwarf
spheroidal (dSph) galaxies suggests that dSph galaxies must be sufficiently
massive (M) that tidal stripping is of little
importance for the stars. We discuss the implications of these massive dSph
galaxies for cosmology and galaxy formation.Comment: 4 pages, 1 figure, to appear in the proceedings of the IAUC198
"Near-Field Cosmology with Dwarf Elliptical Galaxies", H. Jerjen & B.
Binggeli (eds.). Comments welcom
The tidal stripping of satellites
We present an improved analytic calculation for the tidal radius of
satellites and test our results against N-body simulations.
The tidal radius in general depends upon four factors: the potential of the
host galaxy, the potential of the satellite, the orbit of the satellite and
{\it the orbit of the star within the satellite}. We demonstrate that this last
point is critical and suggest using {\it three tidal radii} to cover the range
of orbits of stars within the satellite. In this way we show explicitly that
prograde star orbits will be more easily stripped than radial orbits; while
radial orbits are more easily stripped than retrograde ones. This result has
previously been established by several authors numerically, but can now be
understood analytically. For point mass, power-law (which includes the
isothermal sphere), and a restricted class of split power law potentials our
solution is fully analytic. For more general potentials, we provide an equation
which may be rapidly solved numerically. Over short times (\simlt 1-2 Gyrs
satellite orbit), we find excellent agreement between our analytic and
numerical models. Over longer times, star orbits within the satellite are
transformed by the tidal field of the host galaxy. In a Hubble time, this
causes a convergence of the three limiting tidal radii towards the prograde
stripping radius. Beyond the prograde stripping radius, the velocity dispersion
will be tangentially anisotropic.Comment: 10 pages, 5 figures. Final version accepted for publication in MNRAS.
Some new fully analytic tidal radii have been added for power law density
profiles (including the isothermal sphere) and some split power law
Condensation of `composite bosons' in a rotating BEC
We provide evidence for several novel phases in the dilute limit of rotating
BECs. By exact calculation of wavefunctions and energies for small numbers of
particles, we show that the states near integer angular momentum per particle
are best considered condensates of composite entities, involving vortices and
atoms. We are led to this result by explicit comparison with a description
purely in terms of vortices. Several parallels with the fractional quantum Hall
effect emerge, including the presence of the Pfaffian state.Comment: 4 pages, Latex, 3 figure
Bulk and edge correlations in the compressible half-filled quantum Hall state
We study bulk and edge correlations in the compressible half-filled state,
using a modified version of the plasma analogy. The corresponding plasma has
anomalously weak screening properties, and as a consequence we find that the
correlations along the edge do not decay algebraically as in the Laughlin
(incompressible) case, while the bulk correlations decay in the same way. The
results suggest that due to the strong coupling between charged modes on the
edge and the neutral Fermions in the bulk, reflected by the weak screening in
the plasma analogue, the (attractive) correlation hole is not well defined on
the edge. Hence, the system there can be modeled as a free Fermi gas of {\em
electrons} (with an appropriate boundary condition). We finally comment on a
possible scenario, in which the Laughlin-like dynamical edge correlations may
nevertheless be realized.Comment: package now includes the file epsfig.sty, needed to incorporate
properly the 8 magnificent figure
Ground State Entropy of the Potts Antiferromagnet on Cyclic Strip Graphs
We present exact calculations of the zero-temperature partition function
(chromatic polynomial) and the (exponent of the) ground-state entropy for
the -state Potts antiferromagnet on families of cyclic and twisted cyclic
(M\"obius) strip graphs composed of -sided polygons. Our results suggest a
general rule concerning the maximal region in the complex plane to which
one can analytically continue from the physical interval where . The
chromatic zeros and their accumulation set exhibit the rather
unusual property of including support for and provide further
evidence for a relevant conjecture.Comment: 7 pages, Latex, 4 figs., J. Phys. A Lett., in pres
Magnetic phenomena at and near nu =1/2 and 1/4: theory, experiment and interpretation
I show that the hamiltonian theory of Composite Fermions (CF) is capable of
yielding a unified description in fair agreement with recent experiments on
polarization P and relaxation rate 1/T_1 in quantum Hall states at filling nu =
p/(2ps+1), at and near nu = 1/2 and 1/4, at zero and nonzero temperatures. I
show how rotational invariance and two dimensionality can make the underlying
interacting theory behave like a free one in a limited context.Comment: Latex 4 pages, 2 figure
Charge order, superconductivity, and a global phase diagram of doped antiferromagnets
We investigate the interplay between lattice-symmetry breaking and
superconducting order in a two-dimensional model of doped antiferromagnets,
with long-range Coulomb interactions and Sp(2N) spin symmetry, in the large-N
limit. Our results motivate the outline of a global phase diagram for the
cuprate superconductors. We describe the quantum transitions between the
phases, the evolution of their fermion excitation spectrum, and the
experimental implications.Comment: 4 pages, 4 figs, final version as publishe
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