337 research outputs found
Model C critical dynamics of random anisotropy magnets
We study the relaxational critical dynamics of the three-dimensional random
anisotropy magnets with the non-conserved n-component order parameter coupled
to a conserved scalar density. In the random anisotropy magnets the structural
disorder is present in a form of local quenched anisotropy axes of random
orientation. When the anisotropy axes are randomly distributed along the edges
of the n-dimensional hypercube, asymptotical dynamical critical properties
coincide with those of the random-site Ising model. However structural disorder
gives rise to considerable effects for non-asymptotic critical dynamics. We
investigate this phenomenon by a field-theoretical renormalization group
analysis in the two-loop order. We study critical slowing down and obtain
quantitative estimates for the effective and asymptotic critical exponents of
the order parameter and scalar density. The results predict complex scenarios
for the effective critical exponent approaching an asymptotic regime.Comment: 8 figures, style files include
Phase Transition in the Random Anisotropy Model
The influence of a local anisotropy of random orientation on a ferromagnetic
phase transition is studied for two cases of anisotropy axis distribution. To
this end a model of a random anisotropy magnet is analyzed by means of the
field theoretical renormalization group approach in two loop approximation
refined by a resummation of the asymptotic series. The one-loop result of
Aharony indicating the absence of a second-order phase transition for an
isotropic distribution of random anisotropy axis at space dimension is
corroborated. For a cubic distribution the accessible stable fixed point leads
to disordered Ising-like critical exponents.Comment: 10 pages, 2 latex figures and a style file include
Critical slowing down in random anisotropy magnets
We study the purely relaxational critical dynamics with non-conserved order
parameter (model A critical dynamics) for three-dimensional magnets with
disorder in a form of the random anisotropy axis. For the random axis
anisotropic distribution, the static asymptotic critical behaviour coincides
with that of random site Ising systems. Therefore the asymptotic critical
dynamics is governed by the dynamical exponent of the random Ising model.
However, the disorder influences considerably the dynamical behaviour in the
non-asymptotic regime. We perform a field-theoretical renormalization group
analysis within the minimal subtraction scheme in two-loop approximation to
investigate asymptotic and effective critical dynamics of random anisotropy
systems. The results demonstrate the non-monotonic behaviour of the dynamical
effective critical exponent .Comment: 11 pages, 4 figures, style file include
Functional renormalization group approach to non-collinear magnets
A functional renormalization group approach to -dimensional,
-component, non-collinear magnets is performed using various truncations of
the effective action relevant to study their long distance behavior. With help
of these truncations we study the existence of a stable fixed point for
dimensions between and for various values of focusing on the
critical value that, for a given dimension , separates a first
order region for . Our
approach concludes to the absence of stable fixed point in the physical -
and - cases, in agreement with -expansion and in
contradiction with previous perturbative approaches performed at fixed
dimension and with recent approaches based on conformal bootstrap program.Comment: 16 pages, 8 figure
Інформаційні ресурси з астрономії та їх використання у навчальному процесі
У статті висвітлено огляд сучасних інформаційних ресурсів з астрономії, вітчизняного і закордонного виробництва. Розглядаються найдоступніші програми, які можна використати в підготовці до занять з астрономії.The article provides an overview of modern information resources on astronomy, domestic and foreign. Сited examples the most affordable programs that can be used in preparation for classes in astronomy
Field theory of bicritical and tetracritical points. III. Relaxational dynamics including conservation of magnetization (Model C)
We calculate the relaxational dynamical critical behavior of systems of
symmetry including conservation of magnetization by
renormalization group (RG) theory within the minimal subtraction scheme in two
loop order. Within the stability region of the Heisenberg fixed point and the
biconical fixed point strong dynamical scaling holds with the asymptotic
dynamical critical exponent where is the crossover
exponent and the exponent of the correlation length. The critical
dynamics at and is governed by a small dynamical transient
exponent leading to nonuniversal nonasymptotic dynamical behavior. This may be
seen e.g. in the temperature dependence of the magnetic transport coefficients.Comment: 6 figure
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