1,908 research outputs found
Ground states for a class of deterministic spin models with glassy behaviour
We consider the deterministic model with glassy behaviour, recently
introduced by Marinari, Parisi and Ritort, with \ha\ , where is the discrete sine Fourier transform. The
ground state found by these authors for odd and prime is shown to
become asymptotically dege\-ne\-ra\-te when is a product of odd primes,
and to disappear for even. This last result is based on the explicit
construction of a set of eigenvectors for , obtained through its formal
identity with the imaginary part of the propagator of the quantized unit
symplectic matrix over the -torus.Comment: 15 pages, plain LaTe
On critical phases in anisotropic spin-1 chains
Quantum spin-1 chains may develop massless phases in presence of Ising-like
and single-ion anisotropies. We have studied c=1 critical phases by means of
both analytical techniques, including a mapping of the lattice Hamiltonian onto
an O(2) nonlinear sigma model, and a multi-target DMRG algorithm which allows
for accurate calculation of excited states. We find excellent quantitative
agreement with the theoretical predictions and conclude that a pure Gaussian
model, without any orbifold construction, describes correctly the low-energy
physics of these critical phases. This combined analysis indicates that the
multicritical point at large single-ion anisotropy does not belong to the same
universality class as the Takhtajan-Babujian Hamiltonian as claimed in the
past. A link between string-order correlation functions and twisting vertex
operators, along the c=1 line that ends at this point, is also suggested.Comment: 9 pages, 3 figures, svjour format, submitted to Eur. Phys. J.
Deterministic spin models with a glassy phase transition
We consider the infinite-range deterministic spin models with Hamiltonian
, where is the quantization of a
chaotic map of the torus. The mean field (TAP) equations are derived by summing
the high temperature expansion. They predict a glassy phase transition at the
critical temperature .Comment: 8 pages, no figures, RevTex forma
Investigation of the Neutron Form Factors by Inclusive Quasi-Elastic Scattering of Polarized Electrons off Polarized He: A Theoretical Overview
The theory of quasi-elastic inclusive scattering of polarized leptons off
polarized He is critically reviewed and the origin of different expressions
for the polarized nuclear response function appearing in the literature is
explained. The sensitivity of the longitudinal asymmetry upon the neutron form
factors is thoroughly investigated and the role played by the polarization
angle for minimizing the proton contribution is illustrated.Comment: Phys. Rev C in press; 9 figs. (available upon request
Phase separation and pairing regimes in the one-dimensional asymmetric Hubbard model
We address some open questions regarding the phase diagram of the
one-dimensional Hubbard model with asymmetric hopping coefficients and balanced
species. In the attractive regime we present a numerical study of the passage
from on-site pairing dominant correlations at small asymmetries to
charge-density waves in the region with markedly different hopping
coefficients. In the repulsive regime we exploit two analytical treatments in
the strong- and weak-coupling regimes in order to locate the onset of phase
separation at small and large asymmetries respectively.Comment: 13 pages, RevTeX 4, 12 eps figures, some additional refs. with
respect to v1 and citation errors fixe
Ground-state energies, densities and momentum distributions in closed-shell nuclei calculated within a cluster expansion approach and realistic interactions
A linked cluster expansion suitable for the treatment of ground-state
properties of complex nuclei, as well as of various particle-nucleus scattering
processes, has been used to calculate the ground-state energy, density and
momentum distribution of 16-O and 40-Ca using realistic interactions. First of
all, a benchmark calculation for the ground-state energy has been performed
using the truncated V8' potential, and consisting in the comparison of our
results with the ones obtained by the Fermi Hypernetted Chain approach,
adopting in both cases the same mean field wave functions and the same
correlation functions. The results exhibited a nice agreement between the two
methods. Therefore, the approach has been applied to the calculation of the
ground-state energy, density and momentum distributions of 16-O and 40-Ca using
the full V8' potential, finding again a satisfactory agreement with the results
based on more advanced approaches where higher order cluster contributions are
taken into account. It appears therefore that the cluster expansion approach
can provide accurate approximations for various diagonal and non diagonal
density matrices, so that it could be used for a reliable evaluation of nuclear
effects in various medium and high energy scattering processes off nuclear
targets. The developed approach can be readily generalized to the treatment of
Glauber type final state interaction effects in inclusive, semi-inclusive and
exclusive processes off nuclei at medium and high energies.Comment: 42 pages, 18 figure
Can neutron electromagnetic form factors be obtained by polarized inclusive electron scattering off polarized three-nucleon bound states?
The investigation of the electromagnetic inclusive responses of polarized
He within the plane wave impulse approximation is briefly reported. A
particular emphasys is put on the extraction, from the inclusive responses at
the quasielastic peak, of the neutron form factors from feasible experiments.Comment: 6 pages, Latex, 4 Postscript figures. Presented to XVth Conference on
"Few-body problems in Physics", Groningen July 1997.To appear in Nucl. Phys.
Rapidly-converging methods for the location of quantum critical points from finite-size data
We analyze in detail, beyond the usual scaling hypothesis, the finite-size
convergence of static quantities toward the thermodynamic limit. In this way we
are able to obtain sequences of pseudo-critical points which display a faster
convergence rate as compared to currently used methods. The approaches are
valid in any spatial dimension and for any value of the dynamic exponent. We
demonstrate the effectiveness of our methods both analytically on the basis of
the one dimensional XY model, and numerically considering c = 1 transitions
occurring in non integrable spin models. In particular, we show that these
general methods are able to locate precisely the onset of the
Berezinskii-Kosterlitz-Thouless transition making only use of ground-state
properties on relatively small systems.Comment: 9 pages, 2 EPS figures, RevTeX style. Updated to published versio
Relative entropy via non-sequential recursive pair substitutions
The entropy of an ergodic source is the limit of properly rescaled 1-block
entropies of sources obtained applying successive non-sequential recursive
pairs substitutions (see P. Grassberger 2002 ArXiv:physics/0207023 and D.
Benedetto, E. Caglioti and D. Gabrielli 2006 Jour. Stat. Mech. Theo. Exp. 09
doi:10.1088/1742.-5468/2006/09/P09011). In this paper we prove that the cross
entropy and the Kullback-Leibler divergence can be obtained in a similar way.Comment: 13 pages , 2 figure
Escape orbits and Ergodicity in Infinite Step Billiards
In a previous paper we defined a class of non-compact polygonal billiards,
the infinite step billiards: to a given decreasing sequence of non-negative
numbers , there corresponds a table \Bi := \bigcup_{n\in\N} [n,n+1]
\times [0,p_{n}].
In this article, first we generalize the main result of the previous paper to
a wider class of examples. That is, a.s. there is a unique escape orbit which
belongs to the alpha and omega-limit of every other trajectory. Then, following
a recent work of Troubetzkoy, we prove that generically these systems are
ergodic for almost all initial velocities, and the entropy with respect to a
wide class of ergodic measures is zero.Comment: 27 pages, 8 figure
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