3,034 research outputs found
Various Approaches to Cosmological Gravitational Lensing in Inhomogeneous Models
Gravitational lensing of distant objects caused by gravitational tidal forces
from inhomogeneities in the universe is weak in most cases, but it is noticed
that it gives a great deal of information about the universe, especially
regarding the distribution of dark matter. The statistical values of optical
quantities such as convergence, amplification and shear have been derived by
many people using various approaches, which include the linear perturbational
treatment in the weak limit and the nonlinear treatment considering small-scale
matter distribution.
In this review paper we compare the following three main approaches: (a) the
approach in the multi-lens-plane theory; (b) the approach due to the direct
integration method; and (c) the perturbational approach.
In the former two approaches inhomogeneous matter distributions are produced
in the CDM model using -body simulations (the PM code and the tree-code,
respectively). In (c) the power spectrum corresponding to the CDM model is used
for the large-scale matter distribution.Comment: 30 pages, 13 figure
Motion of the Tippe Top : Gyroscopic Balance Condition and Stability
We reexamine a very classical problem, the spinning behavior of the tippe top
on a horizontal table. The analysis is made for an eccentric sphere version of
the tippe top, assuming a modified Coulomb law for the sliding friction, which
is a continuous function of the slip velocity at the point of
contact and vanishes at . We study the relevance of the gyroscopic
balance condition (GBC), which was discovered to hold for a rapidly spinning
hard-boiled egg by Moffatt and Shimomura, to the inversion phenomenon of the
tippe top. We introduce a variable so that corresponds to the GBC
and analyze the behavior of . Contrary to the case of the spinning egg,
the GBC for the tippe top is not fulfilled initially. But we find from
simulation that for those tippe tops which will turn over, the GBC will soon be
satisfied approximately. It is shown that the GBC and the geometry lead to the
classification of tippe tops into three groups: The tippe tops of Group I never
flip over however large a spin they are given. Those of Group II show a
complete inversion and the tippe tops of Group III tend to turn over up to a
certain inclination angle such that , when they are
spun sufficiently rapidly. There exist three steady states for the spinning
motion of the tippe top. Giving a new criterion for stability, we examine the
stability of these states in terms of the initial spin velocity . And we
obtain a critical value of the initial spin which is required for the
tippe top of Group II to flip over up to the completely inverted position.Comment: 52 pages, 11 figures, to be published in SIAM Journal on Applied
Dynamical Syste
Quantum Electrodynamics at Large Distances III: Verification of Pole Factorization and the Correspondence Principle
In two companion papers it was shown how to separate out from a scattering
function in quantum electrodynamics a distinguished part that meets the
correspondence-principle and pole-factorization requirements. The integrals
that define the terms of the remainder are here shown to have singularities on
the pertinent Landau singularity surface that are weaker than those of the
distinguished part. These remainder terms therefore vanish, relative to the
distinguished term, in the appropriate macroscopic limits. This shows, in each
order of the perturbative expansion, that quantum electrodynamics does indeed
satisfy the pole-factorization and correspondence-principle requirements in the
case treated here. It also demonstrates the efficacy of the computational
techniques developed here to calculate the consequences of the principles of
quantum electrodynamics in the macroscopic and mesoscopic regimes.Comment: latex, 39 pages, 2 Figures included as uuencoded, tarred, gzipped,
encapsulated postscript files, uses math_macros.te
Cyclotron radiation and emission in graphene
Peculiarity in the cyclotron radiation and emission in graphene is
theoretically examined in terms of the optical conductivity and relaxation
rates to propose that graphene in magnetic fields can be a candidate to realize
the Landau level laser, proposed decades ago [H. Aoki, Appl. Phys. Lett. {\bf
48}, 559 (1986)].Comment: 4 pages, 3 figure
Deformable self-propelled particles
A theory of self-propelled particles is developed in two dimensions assuming
that the particles can be deformed from a circular shape when the propagating
velocity is increased. A coupled set of equations in terms of the velocity and
a tensor variable to represent the deformation is introduced to show that there
is a bifurcation from a straight motion to a circular motion of a single
particle. Dynamics of assembly of the particles is studied numerically where
there is a global interaction such that the particles tend to cause an
orientational order.Comment: 4pages, 4figure
RegPT: Direct and fast calculation of regularized cosmological power spectrum at two-loop order
We present a specific prescription for the calculation of cosmological power
spectra, exploited here at two-loop order in perturbation theory (PT), based on
the multi-point propagator expansion. In this approach power spectra are
constructed from the regularized expressions of the propagators that reproduce
both the resummed behavior in the high-k limit and the standard PT results at
low-k. With the help of N-body simulations, we show that such a construction
gives robust and accurate predictions for both the density power spectrum and
the correlation function at percent-level in the weakly non-linear regime. We
then present an algorithm that allows accelerated evaluations of all the
required diagrams by reducing the computational tasks to one-dimensional
integrals. This is achieved by means of pre-computed kernel sets defined for
appropriately chosen fiducial models. The computational time for two-loop
results is then reduced from a few minutes, with the direct method, to a few
seconds with the fast one. The robustness and applicability of this method are
tested against the power spectrum cosmic emulator from which a wide variety of
cosmological models can be explored. The fortran program with which direct and
fast calculations of power spectra can be done, RegPT, is publicly released as
part of this paper.Comment: 28 pages, 15 figure
Momentum-Dependent Hybridization Gap and dispersive in-gap state of The Kondo Semiconductor SmB6
We report the temperature-dependent three-dimensional angle-resolved
photoemission spectra of the Kondo semiconductor SmB. We found a difference
in the temperature dependence of the peaks at the X and points, due to
hybridization between the Sm 5d conduction band and the nearly localized Sm 4f
state. The peak intensity at the X point has the same temperature dependence as
the valence transition below 120 K, while that at the point is
consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This
suggests that the hybridization with the valence transition mainly occurs at
the X point, and the initial state of the magnetic excitation is located at the
point.Comment: 5 pages, 3 figure
Generalized Jarzynski Equality under Nonequilibrium Feedback Control
The Jarzynski equality is generalized to situations in which nonequilibrium
systems are subject to a feedback control. The new terms that arise as a
consequence of the feedback describe the mutual information content obtained by
measurement and the efficacy of the feedback control. Our results lead to a
generalized fluctuation-dissipation theorem that reflects the readout
information, and can be experimentally tested using small thermodynamic
systems. We illustrate our general results by an introducing "information
ratchet," which can transport a Brownian particle in one direction and extract
a positive work from the particle
Quantum-number projection in the path-integral renormalization group method
We present a quantum-number projection technique which enables us to exactly
treat spin, momentum and other symmetries embedded in the Hubbard model. By
combining this projection technique, we extend the path-integral
renormalization group method to improve the efficiency of numerical
computations. By taking numerical calculations for the standard Hubbard model
and the Hubbard model with next nearest neighbor transfer, we show that the
present extended method can extremely enhance numerical accuracy and that it
can handle excited states, in addition to the ground state.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
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