1,447 research outputs found
Stokes phenomenon and matched asymptotic expansions
This paper describes the use of matched asymptotic expansions to illuminate the description of functions exhibiting Stokes phenomenon. In particular the approach highlights the way in which the local structure and the possibility of finding Stokes multipliers explicitly depend on the behaviour of the coefficients of the relevant asymptotic expansions
Correlated exponential functions in high precision calculations for diatomic molecules
Various properties of the general two-center two-electron integral over the
explicitly correlated exponential function are analyzed for the potential use
in high precision calculations for diatomic molecules. A compact one
dimensional integral representation is found, which is suited for the numerical
evaluation. Together with recurrence relations, it makes possible the
calculation of the two-center two-electron integral with arbitrary powers of
electron distances. Alternative approach via the Taylor series in the
internuclear distance is also investigated. Although numerically slower, it can
be used in cases when recurrences lose stability. Separate analysis is devoted
to molecular integrals with integer powers of interelectronic distances
and the vanishing corresponding nonlinear parameter. Several methods
of their evaluation are proposed.Comment: 26 pages, includes two tables with exemplary calculation
On the distribution of the nodal sets of random spherical harmonics
We study the length of the nodal set of eigenfunctions of the Laplacian on
the \spheredim-dimensional sphere. It is well known that the eigenspaces
corresponding to \eigval=n(n+\spheredim-1) are the spaces \eigspc of
spherical harmonics of degree , of dimension \eigspcdim. We use the
multiplicity of the eigenvalues to endow \eigspc with the Gaussian
probability measure and study the distribution of the \spheredim-dimensional
volume of the nodal sets of a randomly chosen function. The expected volume is
proportional to \sqrt{\eigval}. One of our main results is bounding the
variance of the volume to be O(\frac{\eigval}{\sqrt{\eigspcdim}}).
In addition to the volume of the nodal set, we study its Leray measure. For
every , the expected value of the Leray measure is .
We are able to determine that the asymptotic form of the variance is
\frac{const}{\eigspcdim}.Comment: 47 pages, accepted for publication in the Journal of Mathematical
Physics. Lemmas 2.5, 2.11 were proved for any dimension, some other,
suggested by the referee, modifications and corrections, were mad
Statistical physics of power fluctuations in mode locked lasers
We present an analysis of the power fluctuations in the statistical steady
state of a passively mode locked laser. We use statistical light-mode theory to
map this problem to that of fluctuations in a reference equilibrium statistical
physics problem, and in this way study the fluctuations non-perturbatively. The
power fluctuations, being non-critical, are Gaussian and proportional in
amplitude to the inverse square root of the number of degrees of freedom. We
calculate explicit analytic expressions for the covariance matrix of the
overall, pulse and cw power variables, providing complete information on the
single-time power distribution in the laser, and derive a set of
fluctuation-dissipation relations between them and the susceptibilities of the
steady-state quantities.Comment: 7 pages, 1 figure, RevTe
Nearsightedness of Electronic Matter in One Dimension
The concept of nearsightedeness of electronic matter (NEM) was introduced by
W. Kohn in 1996 as the physical principal underlining Yang's electronic
structure alghoritm of divide and conquer. It describes the fact that, for
fixed chemical potential, local electronic properties at a point , like the
density , depend significantly on the external potential only at
nearby points. Changes of that potential, {\it no matter how large},
beyond a distance , have {\it limited} effects on local electronic
properties, which tend to zero as function of . This remains true
even if the changes in the external potential completely surrounds the point
. NEM can be quantitatively characterized by the nearsightedness range,
, defined as the smallest distance from ,
beyond which {\it any} change of the external potential produces a density
change, at , smaller than a given . The present paper gives a
detailed analysis of NEM for periodic metals and insulators in 1D and includes
sharp, explicit estimates of the nearsightedness range. Since NEM involves
arbitrary changes of the external potential, strong, even qualitative changes
can occur in the system, such as the discretization of energy bands or the
complete filling of the insulating gap of an insulator with continuum spectrum.
In spite of such drastic changes, we show that has only a limited
effect on the density, which can be quantified in terms of simple parameters of
the unperturbed system.Comment: 10 pages, 9 figure
Full-analytic frequency-domain 1pN-accurate gravitational wave forms from eccentric compact binaries
The article provides ready-to-use 1pN-accurate frequency-domain gravitational
wave forms for eccentric nonspinning compact binaries of arbitrary mass ratio
including the first post-Newtonian (1pN) point particle corrections to the
far-zone gravitational wave amplitude, given in terms of tensor spherical
harmonics. The averaged equations for the decay of the eccentricity and growth
of radial frequency due to radiation reaction are used to provide stationary
phase approximations to the frequency-domain wave forms.Comment: 28 pages, submitted to PR
High-density correlation energy expansion of the one-dimensional uniform electron gas
We show that the expression of the high-density (i.e small-) correlation
energy per electron for the one-dimensional uniform electron gas can be
obtained by conventional perturbation theory and is of the form \Ec(r_s) =
-\pi^2/360 + 0.00845 r_s + ..., where is the average radius of an
electron. Combining these new results with the low-density correlation energy
expansion, we propose a local-density approximation correlation functional,
which deviates by a maximum of 0.1 millihartree compared to the benchmark DMC
calculations.Comment: 7 pages, 2 figures, 3 tables, accepted for publication in J. Chem.
Phy
Discrete diffraction and shape-invariant beams in optical waveguide arrays
General properties of linear propagation of discretized light in homogeneous
and curved waveguide arrays are comprehensively investigated and compared to
those of paraxial diffraction in continuous media. In particular, general laws
describing beam spreading, beam decay and discrete far-field patterns in
homogeneous arrays are derived using the method of moments and the steepest
descend method. In curved arrays, the method of moments is extended to describe
evolution of global beam parameters. A family of beams which propagate in
curved arrays maintaining their functional shape -referred to as discrete
Bessel beams- is also introduced. Propagation of discrete Bessel beams in
waveguide arrays is simply described by the evolution of a complex
parameter similar to the complex parameter used for Gaussian beams in
continuous lensguide media. A few applications of the parameter formalism
are discussed, including beam collimation and polygonal optical Bloch
oscillations. \Comment: 14 pages, 5 figure
Vector and tensor perturbations in Horava-Lifshitz cosmology
We study cosmological vector and tensor perturbations in Horava-Lifshitz
gravity, adopting the most general Sotiriou-Visser-Weinfurtner generalization
without the detailed balance but with projectability condition. After deriving
the general formulas in a flat FRW background, we find that the vector
perturbations are identical to those given in general relativity. This is true
also in the non-flat cases. For the tensor perturbations, high order
derivatives of the curvatures produce effectively an anisotropic stress, which
could have significant efforts on the high-frequency modes of gravitational
waves, while for the low-frenquency modes, the efforts are negligible. The
power spectrum is scale-invariant in the UV regime, because of the particular
dispersion relations. But, due to lower-order corrections, it will eventually
reduce to that given in GR in the IR limit. Applying the general formulas to
the de Sitter and power-law backgrounds, we calculate the power spectrum and
index, using the uniform approximations, and obtain their analytical
expressions in both cases.Comment: Correct some typos and add new references. Version to be published in
Physical Reviews
Loop Corrections in the Spectrum of 2D Hawking Radiation
We determine the one-loop and the two-loop back-reaction corrections in the
spectrum of the Hawking radiation for the CGHS model of 2d dilaton gravity by
evaluating the Bogoliubov coefficients for a massless scalar field propagating
on the corresponding backgrounds. Since the back-reaction can induce a small
shift in the position of the classical horizon, we find that a positive shift
leads to a non-Planckian late-time spectrum, while a null or a negative shift
leads to a Planckian late-time spectrum in the leading-order stationary-point
approximation. In the one-loop case there are no corrections to the classical
Hawking temperature, while in the two-loop case the temperature is three times
greater than the classical value. We argue that these results are consistent
with the behaviour of the Hawking flux obtained from the operator quantization
only for the times which are not too late, in accordance with the limits of
validity of the semiclassical approximation.Comment: 20 pages, latex, no figure
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