33,988 research outputs found
Zero-temperature TAP equations for the Ghatak-Sherrington model
The zero-temperature TAP equations for the spin-1 Ghatak-Sherrington model
are investigated. The spin-glass energy density (ground state) is determined as
a function of the anisotropy crystal field for a large number of spins.
This allows us to locate a first-order transition between the spin-glass and
paramagnetic phases within a good accuracy. The total number of solutions is
also determined as a function of .Comment: 11 pages, 2 ps figures include
Effects of Random Biquadratic Couplings in a Spin-1 Spin-Glass Model
A spin-1 model, appropriated to study the competition between bilinear
(J_{ij}S_{i}S_{j}) and biquadratic (K_{ij}S_{i}^{2}S_{j}^{2}) random
interactions, both of them with zero mean, is investigated. The interactions
are infinite-ranged and the replica method is employed. Within the
replica-symmetric assumption, the system presents two phases, namely,
paramagnetic and spin-glass, separated by a continuous transition line. The
stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the
random biquadratic couplings between the spins.Comment: 16 pages plus 2 ps figure
Modelagem de Nicho EcolĆ³gico: implicaƧƵes na priorizaĆ§Ć£o de Ć”reas para exploraĆ§Ć£o e liberaĆ§Ć£o de agentes de biocontrole do capim-annoni-2 (Eragrostis plana Nees) no Brasil.
bitstream/item/127272/1/documento-292.pd
Effective restoration of the U_A(1) symmetry with temperature and density
We investigate the full U(3)U(3) chiral symmetry restoration, at
finite temperature and density, on the basis of a quark model which
incorporates the most relevant properties of QCD in this context: explicit and
spontaneous breaking of chiral symmetry and axial U(1) symmetry breaking. A
specific lattice-inspired behavior of the topological susceptibility, combined
with the convergence of chiral partners, signals the onset of an effective
chiral symmetry restoration. The results suggest that the axial part of the
symmetry is restored before the possible restoration of the full
U(3)U(3) chiral symmetry can occur. This conclusion is valid in the
context of both finite temperature and density.Comment: 5 pages, 2 figures; PRD versio
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Can the lack of symmetry in the COBE/DMR maps constrain the topology of the universe?
Although the cubic T^3 ``small universe" has been ruled out by COBE/DMR results as an interesting cosmological model, we still have the possibility of living in a universe with a more anisotropic topology such as a rectangular T^3 ``small universe" with one or two of its dimensions significantly smaller than the present horizon (which we refer to as T^1- and T^2-models, respectively). In order to rule out these anisotropic topologies as well, we apply a new data analysis method that searches for the specific kind of symmetries that these models should produce. We find that the 2 year COBE/DMR data set a lower limit on the smallest cell size for T^1- and T^2-models of 3000 h^{-1} Mpc, at 95% confidence, for a scale invariant power spectrum (n=1). These results imply that {\it all} toroidal universes (cubes and rectangles) are ruled out as interesting cosmological models
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