10,333 research outputs found

### Absence of jump discontinuity in the magnetization in quasi-one-dimensional random-field Ising models

We consider the zero-temperature random-field Ising model in the presence of
an external field, on ladders and in one dimension with finite range
interactions, for unbounded continuous distributions of random fields, and show
that there is no jump discontinuity in the magnetizations for any quasi-one
dimensional model. We show that the evolution of the system at an external
field can be described by a stochastic matrix and the magnetization can be
obtained using the eigenvector of the matrix corresponding to the eigenvalue
one, which is continuous and differentiable function of the external field.Comment: 4 pages, 5 ps figures. Minor correction

### Mode coupling theory in the FDR-preserving field theory of interacting Brownian particles

We develop a renormalized perturbation theory for the dynamics of interacting
Brownian particles, which preserves the fluctuation-dissipation relation order
by order. We then show that the resulting one-loop theory gives a closed
equation for the density correlation function, which is identical with that in
the standard mode coupling theory.Comment: version to be published in Fast Track Communication in Journal of
Physics A:Math. Theo

### Kinetics of the Wako-Saito-Munoz-Eaton Model of Protein Folding

We consider a simplified model of protein folding, with binary degrees of
freedom, whose equilibrium thermodynamics is exactly solvable. Based on this
exact solution, the kinetics is studied in the framework of a local equilibrium
approach, for which we prove that (i) the free energy decreases with time, (ii)
the exact equilibrium is recovered in the infinite time limit, and (iii) the
folding rate is an upper bound of the exact one. The kinetics is compared to
the exact one for a small peptide and to Monte Carlo simulations for a longer
protein, then rates are studied for a real protein and a model structure.Comment: 4 pages, 4 figure

### R-Invariant Topological Inflation

We propose a topological inflation model in the framework of supergravity
with $R$ invariance. This topological inflation model is not only free from the
initial value problem of the inflaton field but also gives low reheating
temperature which is favored in supergravity since the overproduction of
gravitinos is avoided. Furthermore, the predicted spectrum of the density
fluctuations is generally tilted, which will be tested by future observations
on CMB anisotropies and large scale structure of the universe.Comment: 7pages (RevTeX file

### Non-Gaussianity from Baryon Asymmetry

We study a scenario that large non-Gaussianity arises from the baryon
asymmetry of the Universe. There are baryogenesis scenarios containing a light
scalar field, which may result in baryonic isocurvature perturbations with some
amount of non-Gaussianity. As an explicit example we consider the Affleck-Dine
mechanism and show that a flat direction of the supersymmeteric standard model
can generate large non-Gaussianity in the curvature perturbations, satisfying
the observational constraints on the baryonic isocurvature perturbations. The
sign of a non-linearity parameter, f_{NL}, is negative, if the Affleck-Dine
mechanism accounts for the observed baryon asymmetry; otherwise it can be
either positive or negative.Comment: 25 pages, 7 figures; minor correction, references added; version to
appear in JCA

### Dynamic aspect of the chiral phase transition in the mode coupling theory

We analyze the dynamic aspect of the chiral phase transition. We apply the
mode coupling theory to the linear sigma model and derive the kinetic equation
for the chiral phase transition. We challenge Hohenberg and Halperin's
classification scheme of dynamic critical phenomena in which the dynamic
universality class of the chiral phase transition has been identified with that
of the antiferromagnet. We point out a crucial difference between the chiral
dynamics and the antiferromagnet system. We also calculate the dynamic critical
exponent for the chiral phase transition. Our result is $z=1-\eta/2\cong 0.98$
which is contrasted with $z=d/2=1.5$ of the antiferromagnet.Comment: 57 pages, no figure

### Non-equilibrium critical behavior : An extended irreversible thermodynamics approach

Critical phenomena in non-equilibrium systems have been studied by means of a
wide variety of theoretical and experimental approaches. Mode-coupling,
renormalization group, complex Lie algebras and diagrammatic techniques are
some of the usual theoretical tools. Experimental studies include light and
inelastic neutron scattering, X-ray photon correlation spectroscopy, microwave
interferometry and several other techniques. Nevertheless no conclusive
reatment has been developed from the basic principles of a thermodynamic theory
of irreversible processes. We have developed a formalism in which we obtain
correlation functions as field averages of the associated functions. By
applying such formalism we attempt to find out if the resulting correlation
functions will inherit the mathematical properties (integrability, generalized
homogeneity, scaling laws) of its parent potentials, and we will also use these
correlation functions to study the behavior of macroscopic systems far from
equilibrium, specially in the neighborhood of critical points or dynamic phase
transitions. As a working example we will consider the mono-critical behavior
of a non-equilibrium binary fluid mixture close to its consolute point.Comment: 23 pages, 3 figures, 1 tabl

### Stochastic Approach to Flat Direction during Inflation

We revisit the time evolution of a flat and non-flat direction system during
inflation. In order to take into account quantum noises in the analysis, we
base on stochastic formalism and solve coupled Langevin equations numerically.
We focus on a class of models in which tree-level Hubble-induced mass is not
generated. Although the non-flat directions can block the growth of the flat
direction's variance in principle, the blocking effects are suppressed by the
effective masses of the non-flat directions. We find that the fate of the flat
direction during inflation is determined by one-loop radiative corrections and
non-renormalizable terms as usually considered, if we remove the zero-point
fluctuation from the noise terms.Comment: 17 pages, 4 figures, v2: minor corrections made, published in JCA

### 511 keV line and diffuse gamma rays from moduli

We obtain the spectrum of gamma ray emissions from the moduli whose decay
into $e^+ e^-$ accounts for the 511 keV line observed by SPI/INTERGRAL. The
moduli emit gamma rays through internal bremsstrahlung, and also decay directly
into two gammas via tree and/or one-loop diagrams. We show that the internal
bremsstahlung constrains the mass of the moduli below $\sim 40$ MeV
model-independently. On the other hand, the flux of two gammas directly decayed
from the moduli through one loop diagrams will exceed the observed galactic
diffuse gamma-ray background if the moduli mass exceeds $\sim 20$ MeV in the
typical situation. Moreover, forthcoming analysis of SPI data in the range of
1-8 MeV may detect the line emisson with the energy half the moduli mass in the
near future, which confirms the decaying moduli scenario.Comment: 6 pages, 5 figures, published versio

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