8,068 research outputs found
Scaling property and peculiar velocity of global monopoles
We investigate the scaling property of global monopoles in the expanding
universe. By directly solving the equations of motion for scalar fields, we
follow the time development of the number density of global monopoles in the
radiation dominated (RD) universe and the matter dominated (MD) universe. It is
confirmed that the global monopole network relaxes into the scaling regime and
the number per hubble volume is a constant irrespective of the cosmic time. The
number density of global monopoles is given by during the RD era and during the MD era. We also examine the peculiar velocity of global
monopoles. For this purpose, we establish a method to measure the peculiar
velocity by use of only the local quantities of the scalar fields. It is found
that during the RD era and during
the MD era. By use of it, a more accurate analytic estimate for the number
density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.
Cosmological Evolution of Global Monopoles
We investigate the cosmological evolution of global monopoles in the
radiation dominated (RD) and matter dominated (MD) universes by numerically
solving field equations of scalar fields. It is shown that the global monopole
network relaxes into the scaling regime, unlike the gauge monopole network. The
number density of global monopoles is given by during the RD era and during the MD
era. Thus, we have confirmed that density fluctuations produced by global
monopoles become scale invariant and are given by during the RD (MD) era, where is the breaking
scale of the symmetry.Comment: 6 pages, 2 figures, to appear in Phys. Rev. D (R
Nonlocality of the NN interaction in an effective field theory
We investigate low energy nucleon dynamics in the effective field theory
(EFT) of nuclear forces. In leading order of the two-nucleon EFT we show that
nucleon dynamics is governed by the generalized dynamical equation with a
nonlocal-in-time interaction operator. This equation is shown to open new
possibilities for applying the EFT approach to the description of low energy
nucleon dynamics.Comment: 13 pages, 4 figures, REVTeX
Lagrangian evolution of global strings
We establish a method to trace the Lagrangian evolution of extended objects
consisting of a multicomponent scalar field in terms of a numerical calculation
of field equations in three dimensional Eulerian meshes. We apply our method to
the cosmological evolution of global strings and evaluate the energy density,
peculiar velocity, Lorentz factor, formation rate of loops, and emission rate
of Nambu-Goldstone (NG) bosons. We confirm the scaling behavior with a number
of long strings per horizon volume smaller than the case of local strings by a
factor of 10. The strategy and the method established here are
applicable to a variety of fields in physics.Comment: 5 pages, 2 figure
Scaling in Numerical Simulations of Domain Walls
We study the evolution of domain wall networks appearing after phase
transitions in the early Universe. They exhibit interesting dynamical scaling
behaviour which is not yet well understood, and are also simple models for the
more phenomenologically acceptable string networks. We have run numerical
simulations in two- and three-dimensional lattices of sizes up to 4096^3. The
theoretically predicted scaling solution for the wall area density A ~ 1/t is
supported by the simulation results, while no evidence of a logarithmic
correction reported in previous studies could be found. The energy loss
mechanism appears to be direct radiation, rather than the formation and
collapse of closed loops or spheres. We discuss the implications for the
evolution of string networks.Comment: 7pp RevTeX, 9 eps files (including six 220kB ones
Combination of improved multibondic method and the Wang-Landau method
We propose a method for Monte Carlo simulation of statistical physical models
with discretized energy. The method is based on several ideas including the
cluster algorithm, the multicanonical Monte Carlo method and its acceleration
proposed recently by Wang and Landau. As in the multibondic ensemble method
proposed by Janke and Kappler, the present algorithm performs a random walk in
the space of the bond population to yield the state density as a function of
the bond number. A test on the Ising model shows that the number of Monte Carlo
sweeps required of the present method for obtaining the density of state with a
given accuracy is proportional to the system size, whereas it is proportional
to the system size squared for other conventional methods. In addition, the new
method shows a better performance than the original Wang-Landau method in
measurement of physical quantities.Comment: 12 pages, 3 figure
Shot Noise in Digital Holography
We discuss on noise in heterodyne holography in an off-axis configuration. We
show that, for a weak signal, the noise is dominated by the shot noise on the
reference beam. This noise corresponds to an equivalent noise on the signal
beam of one photoelectron per pixel, for the whole sequence of images used to
build the digital hologram
Solving the riddle of codon usage preferences: a test for translational selection
Translational selection is responsible for the unequal usage of synonymous codons in protein coding genes in a wide variety of organisms. It is one of the most subtle and pervasive forces of molecular evolution, yet, establishing the underlying causes for its idiosyncratic behaviour across living kingdoms has proven elusive to researchers over the past 20 years. In this study, a statistical model for measuring translational selection in any given genome is developed, and the test is applied to 126 fully sequenced genomes, ranging from archaea to eukaryotes. It is shown that tRNA gene redundancy and genome size are interacting forces that ultimately determine the action of translational selection, and that an optimal genome size exists for which this kind of selection is maximal. Accordingly, genome size also presents upper and lower boundaries beyond which selection on codon usage is not possible. We propose a model where the coevolution of genome size and tRNA genes explains the observed patterns in translational selection in all living organisms. This model finally unifies our understanding of codon usage across prokaryotes and eukaryotes. Helicobacter pylori, Saccharomyces cerevisiae and Homo sapiens are codon usage paradigms that can be better understood under the proposed model
Coordination and chemical effects on the structural, electronic and magnetic properties in Mn pnictides
Simple structures of MnX binary compounds, namely hexagonal NiAs and
zincblende, are studied as a function of the anion (X = Sb, As, P) by means of
the all-electron FLAPW method within local spin density and generalized
gradient approximations. An accurate analysis of the structural, electronic and
magnetic properties reveals that the cubic structure greatly favours the
magnetic alignment in these compounds leading to high magnetic moments and
nearly half-metallic behaviour for MnSb and MnAs. The effect of the anion
chemical species is related to both its size and the possible hybridization
with the Mn states; both contributions are seen to hinder the magnitude of
the magnetic moment for small and light anions. Our results are in very good
agreement with experiment - where available - and show that the generalized
gradient approximation is essential to correctly recover both the equilibrium
volume and magnetic moment.Comment: 18 pages and 4 figures, Latex-file, submitted to Phys.Rev.
Anomaly-Mediated Supersymmetry Breaking with Axion
We construct hadronic axion models in the framework of the anomaly-mediated
supersymmetry breaking scenario. If the Peccei-Quinn symmetry breaking is
related to the supersymmetry breaking, mass spectrum of the minimal
anomaly-mediated scenario is modified, which may solve the negative slepton
mass problem in the minimal anomaly-mediated model. We find several classes of
phenomenologically viable models of axion within the framework of the anomaly
mediation and, in particular, we point out a new mechanism of stabilizing the
axion potential. In this class of models, the Peccei-Quinn scale is related to
the messenger scale. We also study phenomenological aspects of this class of
models. We will see that, in some case, the lightest particle among the
superpartners of the standard-model particles is stau while the lightest
superparticle becomes the axino, the superpartner of the axion. With such a
unique mass spectrum, conventional studies of the collider physics and
cosmology for supersymmetric models should be altered.Comment: 20 pages, 5 figures, added footnotes and references for section
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