38 research outputs found
The extended gaussian ensemble and metastabilities in the Blume-Capel model
The Blume-Capel model with infinite-range interactions presents analytical
solutions in both canonical and microcanonical ensembles and therefore, its
phase diagram is known in both ensembles. This model exhibits nonequivalent
solutions and the microcanonical thermodynamical features present peculiar
behaviors like nonconcave entropy, negative specific heat, and a jump in the
thermodynamical temperature. Examples of nonequivalent ensembles are in general
related to systems with long-range interactions that undergo canonical
first-order phase transitions. Recently, the extended gaussian ensemble (EGE)
solution was obtained for this model. The gaussian ensemble and its extended
version can be considered as a regularization of the microcanonical ensemble.
They are known to play the role of an interpolating ensemble between the
microcanonical and the canonical ones. Here, we explicitly show how the
microcanonical energy equilibrium states related to the metastable and unstable
canonical solutions for the Blume-Capel model are recovered from EGE, which
presents a concave "extended" entropy as a function of energy.Comment: 6 pages, 5 eps figures. Presented at the XI Latin American Workshop
on Nonlinear Phenomena, October 05-09 (2009), B\'uzios (RJ), Brazil. To
appear in JPC
Comparison among HB-inspired algorithms for continuous-spin systems and gauge fields
We propose a new local algorithm for the thermalization of n-vector spin
models, which can also be used in the numerical simulation of SU(N) lattice
gauge theories. The algorithm combines heat-bath (HB) and micro-canonical
updates in a single step -- as opposed to the hybrid overrelaxation method,
which alternates between the two kinds of update steps -- while preserving
ergodicity. We test our proposed algorithm in the case of the one-dimensional
4-vector spin model and compare its performance with the standard HB algorithm
and with other HB-inspired algorithms.Comment: 6 pages, 4 figures. Work presented at the IV Brazilian Meeting on
Simulational Physics -- Ouro Preto - MG/Brazil, August 200
Thermodynamics of Ising model with infinite-range interactions by generalized canonical ensemble
In this work we present the idea of how generalized ensembles can be used to simplify the operational study of non-additive physical systems. As alternative of the usual methods of direct integration or mean-field theory, we show how the solution of the Ising model with infinite-range interactions is obtained by using a generalized canonical ensemble. We describe how the thermodynamical properties of this model in the presence of an external magnetic field are founded by simple parametric equations. Without impairing the usual interpretation, we obtain an identical critical behaviour as observed in traditional approaches
Screening masses in quenched (2+1)d Yang-Mills theory: universality from dynamics?
We compute the spectrum of gluonic screening-masses in the channel
of quenched 3d Yang-Mills theory near the phase-transition. Our
finite-temperature lattice simulations are performed at scaling region, using
state-of-art techniques for thermalization and spectroscopy, which allows for
thorough data extrapolations to thermodynamic limit. Ratios among
mass-excitations with the same quantum numbers on the gauge theory, 2d Ising
and models are compared, resulting in a nice agreement with
predictions from universality. In addition, a gauge-to-scalar mapping,
previously employed to fit QCD Green's functions at deep IR, is verified to
dynamically describe these universal spectroscopic patternsComment: 15 pages, 4 eps figures. Revised version, to appear in Nucl. Phys.