2,482 research outputs found

### A Classical Solution in Six-dimensional Gauge Theory with Higher Derivative Coupling

We show that the spin connection of the standard metric on a six-dimensional
sphere gives an exact solution to the generalized self-dual equations suggested
by Tchrakian some years ago. We work on an SO(6) gauge theory with a
higher-derivative coupling term. The model consists of vector fields only. The
pseudo-energy is bound from below by a topological charge which is proportional
to the winding number of spatial S^5 around the internal space SO(6). The fifth
homotopy group of SO(6) is, indeed, Z. The coupling constant of higher
derivative term is quadratic in the radius of the underlying space S^6.Comment: 7 pages, comments and a reference added, typos correcte

### Long term ordering kinetics of the two dimensional q-state Potts model

We studied the non-equilibrium dynamics of the q-state Potts model in the
square lattice, after a quench to sub-critical temperatures. By means of a
continuous time Monte Carlo algorithm (non-conserved order parameter dynamics)
we analyzed the long term behavior of the energy and relaxation time for a wide
range of quench temperatures and system sizes. For q>4 we found the existence
of different dynamical regimes, according to quench temperature range. At low
(but finite) temperatures and very long times the Lifshitz-Allen-Cahn domain
growth behavior is interrupted with finite probability when the system stuck in
highly symmetric non-equilibrium metastable states, which induce activation in
the domain growth, in agreement with early predictions of Lifshitz [JETP 42,
1354 (1962)]. Moreover, if the temperature is very low, the system always gets
stuck at short times in a highly disordered metastable states with finite life
time, which have been recently identified as glassy states. The finite size
scaling properties of the different relaxation times involved, as well as their
temperature dependency are analyzed in detail.Comment: 10 pages, 17 figure

### Multiferroic properties of an \aa kermanite Sr$_2$CoSi$_2$O$_7$ single crystal in high magnetic fields

The magnetic and dielectric properties of \aa kermanite Sr$_2$CoSi$_2$O$_7$
single crystals in high magnetic fields were investigated. We have observed
finite induced electric polarization along the c axis in high fields, wherein
all Co spins were forcibly aligned to the magnetic field direction. Existence
of the induced polarization in the spin-polarized state accompanied with the
finite slope in the magnetization curve suggests the possible role of the
orbital angular momenta in the excited states as its microscopic origin. The
emergence of the field-induced polarization without particular magnetic order
can be regarded as the magnetoelectric effects of the second order from the
symmetry point of view. A low magnetic field-driven electric polarization flip
induced by a rotating field, even at room temperature, has been successfully
demonstrated.Comment: 12 pages, 4 figure

### Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard sphere solvents

Monte Carlo computer simulations are used to study transient cavities and the
solvation of hard-spheroid solutes in dipolar hard sphere solvents. The
probability distribution of spheroidal cavities in the solvent is shown to be
well described by a Gaussian function, and the variations of fit parameters
with cavity elongation and solvent properties are analyzed. The excess chemical
potentials of hard-spheroid solutes with aspect ratios $x$ in the range $1/5
\leq x \leq 5$, and with volumes between one and twenty times that of a solvent
molecule, are presented. It is shown that for a given molecular volume and
solvent dipole moment (or temperature) a spherical solute has the lowest excess
chemical potential and hence the highest solubility, while a prolate solute
with aspect ratio $x$ should be more soluble than an oblate solute with aspect
ratio $1/x$. For a given solute molecule, the excess chemical potential
increases with increasing temperature; this same trend is observed in the case
of hydrophobic solvation. To help interpret the simulation results, comparison
is made with a scaled-particle theory that requires prior knowledge of a
solute-solvent interfacial tension and the pure-solvent equation of state,
which parameters are obtained from simulation results for spherical solutes.
The theory shows excellent agreement with simulation results over the whole
range of solute elongations considered.Comment: 10 pages, 10 figure

### Scale Invariance in a Perturbed Einstein-de Sitter Cosmology

This paper seeks to check the validity of the "apparent fractal conjecture"
(Ribeiro 2001ab: gr-qc/9909093, astro-ph/0104181), which states that the
observed power-law behaviour for the average density of large-scale
distribution of galaxies arises when some observational quantities, selected by
their relevance in average density profile determination, are calculated along
the past light cone. Implementing these conditions in the proposed set of
observational relations profoundly changes the behaviour of many observables in
the standard cosmological models. In particular, the average density becomes
observationally inhomogeneous, even in the spatially homogeneous spacetime of
standard cosmology, change which was already analysed by Ribeiro (1992b, 1993,
1994, 1995: astro-ph/9910145) for a non-perturbed model. Here we derive
observational relations in a perturbed Einstein-de Sitter cosmology by means of
the perturbation scheme proposed by Abdalla and Mohayaee (1999:
astro-ph/9810146), where the scale factor is expanded in power series to yield
perturbative terms. The differential equations derived in this perturbative
context, and other observables necessary in our analysis, are solved
numerically. The results show that our perturbed Einstein-de Sitter cosmology
can be approximately described by a decaying power-law like average density
profile, meaning that the dust distribution of this cosmology has a scaling
behaviour compatible with the power-law profile of the density-distance
correlation observed in the galaxy catalogues. These results show that, in the
context of this work, the apparent fractal conjecture is correct.Comment: 18 pages, 1 figure, LaTeX. Final version (small changes in the figure
plus some references update). Fortran code included with the LaTeX source. To
be published in "Fractals

### Magnetic and Dielectric Properties in Multiferroic Cu3Mo2O9 under High Magnetic Fields

The magnetic and dielectric properties under high magnetic fields are studied
in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted
tetrahedral spin chains. The effects of the quasi-one dimensionality and the
geometrical spin frustration are expected to appear simultaneously. We measure
the magnetoelectric current and the differential magnetization under the pulsed
magnetic field up to 74 T. We also measure the electric polarization versus the
electric field curve/loop under the static field up to 23 T. Dielectric
properties change at the magnetic fields where the magnetization jumps are
observed in the magnetization curve. Moreover, the magnetization plateaus are
found at high magnetic fields.Comment: 6 pages, 3 figures, in press in JPS Conf. Proc. as a part of SCES2013
Proceeding

### Dynamical Compactification and Inflation in Einstein-Yang-Mills Theory with Higher Derivative Coupling

We study cosmology of the Einstein-Yang-Mills theory in ten dimensions with a
quartic term in the Yang-Mills field strength. We obtain analytically a class
of cosmological solutions in which the extra dimensions are static and the
scale factor of the four-dimensional Friedmann-Lemaitre-Robertson-Walker metric
is an exponential function of time. This means that the model can explain
inflation. Then we look for solutions that describe dynamical compactification
of the extra dimensions. The effective cosmological constant $\lambda_1$ in the
four-dimensional universe is determined from the gravitational coupling,
ten-dimensional cosmological constant, gauge coupling and higher derivative
coupling. By numerical integration, the solution with $\lambda_1=0$ is found to
behave as a matter-dominated universe which asymptotically approaches flat
space-time, while the solution with a non-vanishing $\lambda_1$ approaches de
Sitter space-time in the asymptotic future.Comment: 30 pages, 7 figure

### Internal Energy of the Potts model on the Triangular Lattice with Two- and Three-body Interactions

We calculate the internal energy of the Potts model on the triangular lattice
with two- and three-body interactions at the transition point satisfying
certain conditions for coupling constants. The method is a duality
transformation. Therefore we have to make assumptions on uniqueness of the
transition point and that the transition is of second order. These assumptions
have been verified to hold by numerical simulations for q=2, 3 and 4, and our
results for the internal energy are expected to be exact in these cases.Comment: 9 pages, 4 figure

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