1,478 research outputs found
Constrained Lp-Approximation by Generalized n-Convex Functions Induced by ECT-Systems
AbstractThe problem of finding a best Lp-approximation (1 ≤ p < ∞) to a function in Lp from a special subcone of generalized n-convex functions induced by an ECT-system is considered. Tchebycheff splines with a countably infinite number of knots are introduced and best approximations are characterized in terms of local best approximations by these splines. Various properties of best approximations and their uniqueness in L1 are investigated. Some special results for generalized monotone and convex cases are obtained
Hard diffractive quarkonium hadroproduction at high energies
We present a study of heavy quarkonium production in hard diffractive process
by the Pomeron exchange for Tevatron and LHC energies. The numerical results
are computed using recent experimental determination of the diffractive parton
density functions in Pomeron and are corrected by unitarity corrections through
gap survival probability factor. We give predictions for single as well as
central diffractive ratios. These processes are sensitive to the gluon content
of the Pomeron at small Bjorken-x and may be particularly useful in studying
the small-x physics. They may also be a good place to test the different
available mechanisms for quarkonium production at hadron colliders.Comment: 7 pages, 3 figures, 1 table. Final version to be published in
European Physical Journal
Supersymmetric Regularization, Two-Loop QCD Amplitudes and Coupling Shifts
We present a definition of the four-dimensional helicity (FDH) regularization
scheme valid for two or more loops. This scheme was previously defined and
utilized at one loop. It amounts to a variation on the standard 't
Hooft-Veltman scheme and is designed to be compatible with the use of helicity
states for "observed" particles. It is similar to dimensional reduction in that
it maintains an equal number of bosonic and fermionic states, as required for
preserving supersymmetry. Supersymmetry Ward identities relate different
helicity amplitudes in supersymmetric theories. As a check that the FDH scheme
preserves supersymmetry, at least through two loops, we explicitly verify a
number of these identities for gluon-gluon scattering (gg to gg) in
supersymmetric QCD. These results also cross-check recent non-trivial two-loop
calculations in ordinary QCD. Finally, we compute the two-loop shift between
the FDH coupling and the standard MS-bar coupling, alpha_s. The FDH shift is
identical to the one for dimensional reduction. The two-loop coupling shifts
are then used to obtain the three-loop QCD beta function in the FDH and
dimensional reduction schemes.Comment: 44 pages, minor corrections and clarifications include
Wick type deformation quantization of Fedosov manifolds
A coordinate-free definition for Wick-type symbols is given for symplectic
manifolds by means of the Fedosov procedure. The main ingredient of this
approach is a bilinear symmetric form defined on the complexified tangent
bundle of the symplectic manifold and subject to some set of algebraic and
differential conditions. It is precisely the structure which describes a
deviation of the Wick-type star-product from the Weyl one in the first order in
the deformation parameter. The geometry of the symplectic manifolds equipped by
such a bilinear form is explored and a certain analogue of the
Newlander-Nirenberg theorem is presented. The 2-form is explicitly identified
which cohomological class coincides with the Fedosov class of the Wick-type
star-product. For the particular case of K\"ahler manifold this class is shown
to be proportional to the Chern class of a complex manifold. We also show that
the symbol construction admits canonical superextension, which can be thought
of as the Wick-type deformation of the exterior algebra of differential forms
on the base (even) manifold. Possible applications of the deformed superalgebra
to the noncommutative field theory and strings are discussed.Comment: 20 pages, no figure
Prospects in the orbital and rotational dynamics of the Moon with the advent of sub-centimeter lunar laser ranging
Lunar Laser Ranging (LLR) measurements are crucial for advanced exploration
of the laws of fundamental gravitational physics and geophysics. Current LLR
technology allows us to measure distances to the Moon with a precision
approaching 1 millimeter. As NASA pursues the vision of taking humans back to
the Moon, new, more precise laser ranging applications will be demanded,
including continuous tracking from more sites on Earth, placing new CCR arrays
on the Moon, and possibly installing other devices such as transponders, etc.
Successful achievement of this goal strongly demands further significant
improvement of the theoretical model of the orbital and rotational dynamics of
the Earth-Moon system. This model should inevitably be based on the theory of
general relativity, fully incorporate the relevant geophysical processes, lunar
librations, tides, and should rely upon the most recent standards and
recommendations of the IAU for data analysis. This paper discusses methods and
problems in developing such a mathematical model. The model will take into
account all the classical and relativistic effects in the orbital and
rotational motion of the Moon and Earth at the sub-centimeter level. The new
model will allow us to navigate a spacecraft precisely to a location on the
Moon. It will also greatly improve our understanding of the structure of the
lunar interior and the nature of the physical interaction at the core-mantle
interface layer. The new theory and upcoming millimeter LLR will give us the
means to perform one of the most precise fundamental tests of general
relativity in the solar system.Comment: 26 pages, submitted to Proc. of ASTROCON-IV conference (Princeton
Univ., NJ, 2007
Electronic structure, phase stability and chemical bonding in ThAl and ThAlH
We present the results of theoretical investigation on the electronic
structure, bonding nature and ground state properties of ThAl and
ThAlH using generalized-gradient-corrected first-principles
full-potential density-functional calculations. ThAlH has been reported
to violate the "2 \AA rule" of H-H separation in hydrides. From our total
energy as well as force-minimization calculations, we found a shortest H-H
separation of 1.95 {\AA} in accordance with recent high resolution powder
neutron diffraction experiments. When the ThAl matrix is hydrogenated, the
volume expansion is highly anisotropic, which is quite opposite to other
hydrides having the same crystal structure. The bonding nature of these
materials are analyzed from the density of states, crystal-orbital Hamiltonian
population and valence-charge-density analyses. Our calculation predicts
different nature of bonding for the H atoms along and . The strongest
bonding in ThAlH is between Th and H along which form dumb-bell
shaped H-Th-H subunits. Due to this strong covalent interaction there is very
small amount of electrons present between H atoms along which makes
repulsive interaction between the H atoms smaller and this is the precise
reason why the 2 {\AA} rule is violated. The large difference in the
interatomic distances between the interstitial region where one can accommodate
H in the and planes along with the strong covalent interaction
between Th and H are the main reasons for highly anisotropic volume expansion
on hydrogenation of ThAl.Comment: 14 pages, 9 figure
Dissociation cross sections of ground-state and excited charmonia with light mesons in the quark model
We present numerical results for the dissociation cross sections of
ground-state, orbitally- and radially-excited charmonia in collisions with
light mesons. Our results are derived using the nonrelativistic quark model, so
all parameters are determined by fits to the experimental meson spectrum.
Examples of dissociation into both exclusive and inclusive final states are
considered. The dissociation cross sections of several C=(+) charmonia may be
of considerable importance for the study of heavy ion collisions, since these
states are expected to be produced more copiously than the J/psi. The relative
importance of the productions of ground-state and orbitally-excited charmed
mesons in a pion-charmonium collision is demonstrated through the -dependent charmonium dissociation cross sections.Comment: 9 pages, 8 figure
Fine Splitting of Electron States in Silicon Nanocrystal with a Hydrogen-like Shallow Donor
Electron structure of a silicon quantum dot doped with a shallow hydrogen-like donor has been calculated for the electron states above the optical gap. Within the framework of the envelope-function approach we have calculated the fine splitting of the ground sixfold degenerate electron state as a function of the donor position inside the quantum dot. Also, dependence of the wave functions and energies on the dot size was obtained
Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, He, and C
Multiple emission of intermediate-mass fragments has been studied for the
collisions of p, He and C on Au with the setup FASA. The mean
IMF multiplicities (for the events with at least one IMF) are saturating at the
value of for the incident energies above 6 GeV. The observed IMF
multiplicities cannot be described in a two-stage scenario, a fast cascade
followed by a statistical multifragmentation. Agreement with the measured IMF
multiplicities is obtained by introducing an intermediate phase and modifying
empirically the excitation energies and masses of the remnants.
The angular distributions and energy spectra from the p-induced collisions
are in agreement with the scenario of ``thermal'' multifragmentation of a hot
and diluted target spectator. In the case of C+Au(22.4 GeV) and
He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are
seen in the energy spectra of the emitted fragments, which are harder than
those both from model calculations and from the measured ones for p-induced
collisions. This difference is attributed to a collective flow.Comment: 33 pages 15 figures, accepted in Nucl. Phys.
Recent glitches detected in the Crab pulsar
From 2000 to 2010, monitoring of radio emission from the Crab pulsar at
Xinjiang Observatory detected a total of nine glitches. The occurrence of
glitches appears to be a random process as described by previous researches. A
persistent change in pulse frequency and pulse frequency derivative after each
glitch was found. There is no obvious correlation between glitch sizes and the
time since last glitch. For these glitches and
span two orders of magnitude. The pulsar suffered the
largest frequency jump ever seen on MJD 53067.1. The size of the glitch is
6.8 Hz, 3.5 times that of the glitch occured in
1989 glitch, with a very large permanent changes in frequency and pulse
frequency derivative and followed by a decay with time constant 21 days.
The braking index presents significant changes. We attribute this variation to
a varying particle wind strength which may be caused by glitch activities. We
discuss the properties of detected glitches in Crab pulsar and compare them
with glitches in the Vela pulsar.Comment: Accepted for publication in Astrophysics & Space Scienc
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