782 research outputs found
The spectrum of an open vertex model based on the U_q[SU(2)] at roots of unity
We study the exact solution of an -state vertex model based on the
representation of the algebra at roots of unity with diagonal open
boundaries. We find that the respective reflection equation provides us one
general class of diagonal -matrices having one free-parameter. We determine
the eigenvalues of the double-row transfer matrix and the respective Bethe
ansatz equation within the algebraic Bethe ansatz framework. The structure of
the Bethe ansatz equation combine a pseudomomenta function depending on a
free-parameter with scattering phase-shifts that are fixed by the roots of
unity and boundary variables.Comment: 21 page
Bethe ansatz for the XXX-S chain with non-diagonal open boundaries
We consider the algebraic Bethe ansatz solution of the integrable and
isotropic XXX-S Heisenberg chain with non-diagonal open boundaries. We show
that the corresponding K-matrices are similar to diagonal matrices with the
help of suitable transformations independent of the spectral parameter. When
the boundary parameters satisfy certain constraints we are able to formulate
the diagonalization of the associated double-row transfer matrix by means of
the quantum inverse scattering method. This allows us to derive explicit
expressions for the eigenvalues and the corresponding Bethe ansatz equations.
We also present evidences that the eigenvectors can be build up in terms of
multiparticle states for arbitrary S.Comment: 62 page
Algebraic Bethe Ansatz for U(1) Invariant Integrable Models: The Method and General Results
In this work we have developed the essential tools for the algebraic Bethe
ansatz solution of integrable vertex models invariant by a unique U(1) charge
symmetry. The formulation is valid for arbitrary statistical weights and
respective number of edge states. We show that the fundamental commutation
rules between the monodromy matrix elements are derived by solving linear
systems of equations. This makes possible the construction of the transfer
matrix eigenstates by means of a new recurrence relation depending on
distinct types of creation fields. The necessary identities to solve the
eigenvalue problem are obtained exploring the unitarity property and the
Yang-Baxter equation satisfied by the -matrix. The on-shell and off-shell
properties of the algebraic Bethe ansatz are explicitly presented in terms of
the arbitrary -matrix elements. This includes the transfer matrix
eigenvalues, the Bethe ansatz equations and the structure of the vectors not
parallel to the eigenstates.Comment: 90 page
The Bethe ansatz approach for factorizable centrally extended S-matrices
We consider the Bethe ansatz solution of integrable models interacting
through factorized -matrices based on the central extention of the
symmetry. The respective -matrix is explicitly
related to that of the covering Hubbard model through a spectral parameter
dependent transformation. This mapping allows us to diagonalize inhomogeneous
transfer matrices whose statistical weights are given in terms of
-matrices by the algebraic Bethe ansatz. As a consequence of
that we derive the quantization condition on the circle for the asymptotic
momenta of particles scattering by the
-matrix. The result for the quantization rule may be of relevance in the
study of the energy spectrum of the string sigma model in
the thermodynamic limit. \Comment: 22 pages, published versio
Restructuring of the "Macaronesia" biogeografic unit: a marine multi-taxon biogeographical approach
The Azores, Madeira, Selvagens, Canary Islands and Cabo Verde are commonly united under the term
“Macaronesia”. This study investigates the coherency and validity of Macaronesia as a biogeographic
unit using six marine groups with very different dispersal abilities: coastal fishes, echinoderms,
gastropod molluscs, brachyuran decapod crustaceans, polychaete annelids, and macroalgae. We found
no support for the current concept of Macaronesia as a coherent marine biogeographic unit. All marine
groups studied suggest the exclusion of Cabo Verde from the remaining Macaronesian archipelagos and thus, Cabo Verde should be given the status of a biogeographic subprovince within the West African
Transition province. We propose to redefine the Lusitanian biogeographical province, in which we
include four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores, and a
new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and
the Canary Islandsinfo:eu-repo/semantics/publishedVersio
A nonlinear hydrodynamical approach to granular materials
We propose a nonlinear hydrodynamical model of granular materials. We show
how this model describes the formation of a sand pile from a homogeneous
distribution of material under gravity, and then discuss a simulation of a
rotating sandpile which shows, in qualitative agreement with experiment, a
static and dynamic angle of repose.Comment: 17 pages, 14 figures, RevTeX4; minor changes to wording and some
additional discussion. Accepted by Phys. Rev.
Stripes, Pseudogaps, and Van Hove Nesting in the Three-band tJ Model
Slave boson calculations have been carried out in the three-band tJ model for
the high-T_c cuprates, with the inclusion of coupling to oxygen breathing mode
phonons. Phonon-induced Van Hove nesting leads to a phase separation between a
hole-doped domain and a (magnetic) domain near half filling, with long-range
Coulomb forces limiting the separation to a nanoscopic scale. Strong
correlation effects pin the Fermi level close to, but not precisely at the Van
Hove singularity (VHS), which can enhance the tendency to phase separation. The
resulting dispersions have been calculated, both in the uniform phases and in
the phase separated regime. In the latter case, distinctly different
dispersions are found for large, random domains and for regular (static)
striped arrays, and a hypothetical form is presented for dynamic striped
arrays. The doping dependence of the latter is found to provide an excellent
description of photoemission and thermodynamic experiments on pseudogap
formation in underdoped cuprates. In particular, the multiplicity of observed
gaps is explained as a combination of flux phase plus charge density wave (CDW)
gaps along with a superconducting gap. The largest gap is associated with VHS
nesting. The apparent smooth evolution of this gap with doping masks a
crossover from CDW-like effects near optimal doping to magnetic effects (flux
phase) near half filling. A crossover from large Fermi surface to hole pockets
with increased underdoping is found. In the weakly overdoped regime, the CDW
undergoes a quantum phase transition (), which could be obscured
by phase separation.Comment: 15 pages, Latex, 18 PS figures Corrects a sign error: major changes,
esp. in Sect. 3, Figs 1-4,6 replace
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