10 research outputs found
Two and Three-Dimensional Spin Systems with Gonihedric Action
We perform numerical simulations of the two and three-dimensional spin
systems with competing interaction. They describe the model of random surfaces
with linear-gonihedric action.The degeneracy of the vacuum state of this spin
system is equal to for the lattice of the size .
We observe the second order phase transition of the three-dimensional system,
at temperature which almost coincides with
of the 2D Ising model. This confirms the earlier analytical result
for the case when self-interaction coupling constant is equal to zero. We
suggest the full set of order parameters which characterize the structure of
the vacuum states and of the phase transition.Comment: 10 pages,Latex,The figures are availabl
Evidence for a first order transition in a plaquette 3d Ising-like action
We investigate a 3d Ising action which corresponds to a a class of models
defined by Savvidy and Wegner, originally intended as discrete versions of
string theories on cubic lattices. These models have vanishing bare surface
tension and the couplings are tuned in such a way that the action depends only
on the angles of the discrete surface, i.e. on the way the surface is embedded
in . Hence the name gonihedric by which they are known. We show that
the model displays a rather clear first order phase transition in the limit
where self-avoidance is neglected and the action becomes a plaquette one. This
transition persists for small values of the self avoidance coupling, but it
turns to second order when this latter parameter is further increased. These
results exclude the use of this type of action as models of gonihedric random
surfaces, at least in the limit where self avoidance is neglected.Comment: 4 pages Latex text, 4 postscript figure
String tension in gonihedric 3D Ising models
For the 3D gonihedric Ising models defined by Savvidy and Wegner the bare
string tension is zero and the energy of a spin interface depends only on the
number of bends and self-intersections, in antithesis to the standard
nearest-neighbour 3D Ising action. When the parameter kappa weighting the
self-intersections is small the model has a first order transition and when it
is larger the transition is continuous.
In this paper we investigate the scaling of the renormalized string tension,
which is entirely generated by fluctuations, using Monte Carlo simulations This
allows us to obtain an estimate for the critical exponents alpha and nu using
both finite-size-scaling and data collapse for the scaling function.Comment: Latex + postscript figures. 8 pages text plus 7 figures, spurious
extra figure now removed
The S-Wave in the 1 to 2 GeV Region from a , and () Coupled Channel Model
A simple , , and () fully
coupled channel model is proposed to predict the isoscalar S-wave phase shifts
and inelasticities for scattering in the 1.0 to 2.0 GeV region. The
S-matrix is required to exhibit poles corresponding to the established
isoscalar J = 0 resonances f(975), f(1400), and
f(1710). A dominant feature of the experimental inelasticity is
the clear opening of the channel near 1 GeV, and the opening of
another channel in the 1.4 - 1.5 GeV region. The success of our model in
predicting this observed dramatic energy dependence indicates that the effect
of multi-pion channels is adequately described by the coupling to the
channel, the (4) and (6)
channels.Comment: 11 pages (Revtex 3.0), 4 figs. avail. upon request, RU946
Three-dimensional Gonihedric Potts model
We study, by the Mean Field and Monte Carlo methods, a generalized q-state
Potts gonihedric model. The phase transition of the model becomes stronger with
increasing The value at which the phase transition becomes
second order, turns out to be an increasing function of Comment: 11 pages, 7 figure
Slow dynamics in the 3--D gonihedric model
We study dynamical aspects of three--dimensional gonihedric spins by using
Monte--Carlo methods. The interest of this family of models (parametrized by
one self-avoidance parameter ) lies in their capability to show
remarkably slow dynamics and seemingly glassy behaviour below a certain
temperature without the need of introducing disorder of any kind. We
consider first a hamiltonian that takes into account only a four--spin term
(), where a first order phase transition is well established. By
studying the relaxation properties at low temperatures we confirm that the
model exhibits two distinct regimes. For , with long lived
metastability and a supercooled phase, the approach to equilibrium is well
described by a stretched exponential. For the dynamics appears to be
logarithmic. We provide an accurate determination of . We also determine
the evolution of particularly long lived configurations. Next, we consider the
case , where the plaquette term is absent and the gonihedric action
consists in a ferromagnetic Ising with fine-tuned next-to-nearest neighbour
interactions. This model exhibits a second order phase transition. The
consideration of the relaxation time for configurations in the cold phase
reveals the presence of slow dynamics and glassy behaviour for any .
Type II aging features are exhibited by this model.Comment: 13 pages, 12 figure
Annihilation range and final-state interaction in the antiproton-proton annihilation into pi-pi+
The large set of accurate data on differential cross section and analyzing
power from the CERN LEAR experiment on in the range
from 360 to 1550 MeV/c is well reproduced within a distorted wave approximation
approach. The initial scattering wave functions originate from a
recent model. The transition operator is obtained from a combination
of the and quark-antiquark annihilation mechanisms. A good fit
to the data, in particular the reproduction of the double dip structure
observed in the analyzing powers, requires quark wave functions for proton,
antiproton, and pions with radii slightly larger than the respective measured
charge radii. This corresponds to an increase in range of the annihilation
mechanisms and consequently the amplitudes for total angular momentum J=2 and
higher are much larger than in previous approaches. The final state
wave functions, parameterized in terms of phase shifts and
inelasticities, are also a very important ingredient for the fine tuning of the
fit to the observables.Comment: 11 pages, 11 figures (Revtex 4), revised version with one additional
figure. Accepted for publication in PR
An amplitude analysis of the reaction
A simple partial wave amplitude analysis of has been performed for data in the range p_{\sl lab} = 360 -- 1000
MeV/c. Remarkably few partial waves are required to fit the data, while the
number of required values barely changes over this energy range. However,
the resulting set of partial wave amplitudes is not unique. We discuss possible
measurements with polarized beam and target which will severely restrict and
help resolve the present analysis ambiguities. New data from the reaction
alone, are insufficient for that
purpose.Comment: 16 pages (revtex), 8 figures available on request, submitted to Phys.
Rev.