175,595 research outputs found
Vacuum polarization radiative correction to the parity violating electron scattering on heavy nuclei
The effect of vacuum polarization on the parity violating asymmetry in the
elastic electron-nucleus scattering is considered. Calculations are performed
in the high-energy approximation with an exact account for the electric field
of the nucleus. It is shown that the radiative correction to the parity
violating asymmetry is logarithmically enhanced and the value of the correction
is about -1%.Comment: 6 pages, 3 figures, REVTex
Observation potential for \chi_b at the Tevatron and LHC
We confirm the results of previous works that the internal motion of quarks
inside charmonium mesons increases the cross section of the process J/\psi\eta_c\chi_{b0,2}\to2J/\psi$ can be used to detect these scalar mesons at Tevatron
and LHC colliders.Comment: 13 pages, 5 figures, error in fig.3 correcte
Navigation and flight director guidance for the NASA/FAA helicopter MLS curved approach flight test program
The navigation and flight director guidance systems implemented in the NASA/FAA helicopter microwave landing system (MLS) curved approach flight test program is described. Flight test were conducted at the U.S. Navy's Crows Landing facility, using the NASA Ames UH-lH helicopter equipped with the V/STOLAND avionics system. The purpose of these tests was to investigate the feasibility of flying complex, curved and descending approaches to a landing using MLS flight director guidance. A description of the navigation aids used, the avionics system, cockpit instrumentation and on-board navigation equipment used for the flight test is provided. Three generic reference flight paths were developed and flown during the test. They were as follows: U-Turn, S-turn and Straight-In flight profiles. These profiles and their geometries are described in detail. A 3-cue flight director was implemented on the helicopter. A description of the formulation and implementation of the flight director laws is also presented. Performance data and analysis is presented for one pilot conducting the flight director approaches
Evaluating `elliptic' master integrals at special kinematic values: using differential equations and their solutions via expansions near singular points
This is a sequel of our previous paper where we described an algorithm to
find a solution of differential equations for master integrals in the form of
an -expansion series with numerical coefficients. The algorithm is
based on using generalized power series expansions near singular points of the
differential system, solving difference equations for the corresponding
coefficients in these expansions and using matching to connect series
expansions at two neighboring points. Here we use our algorithm and the
corresponding code for our example of four-loop generalized sunset diagrams
with three massive and two massless propagators, in order to obtain new
analytical results. We analytically evaluate the master integrals at threshold,
, in an expansion in up to . With the help of
our code, we obtain numerical results for the threshold master integrals in an
-expansion with the accuracy of 6000 digits and then use the PSLQ
algorithm to arrive at analytical values. Our basis of constants is build from
bases of multiple polylogarithm values at sixth roots of unity.Comment: Discussion extende
Continuum in the spin excitation spectrum of a Haldane chain, observed by neutron scattering in CsNiCl3
The spin excitation continuum, expected to dominate the low-energy
fluctuation spectrum in the Haldane spin chain around the Brillouin zone
center, q=0, is directly observed by inelastic magnetic neutron scattering in
the S=1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode
approximation fails, and that a finite energy width appears in the dynamic
correlation function S(q,omega) for q < 0.5pi. The width increases with
decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively
similar to that predicted for the 2-magnon continuum in the nonlinear
sigma-model.Comment: 4 pages, 3 figures, submitted to PR
QCD sum rules for the anti-charmed pentaquark
We present a QCD sum rule analysis for the anti-charmed pentaquark state with
and without strangeness. While the sum rules for most of the currents are
either non-convergent or dominated by the continuum, the one for the
non-strange pentaquark current composed of two diquarks and an antiquark, is
convergent and has a structure consistent with a positive parity pentaquark
state after subtracting out the continuum contribution. Arguments are
presented on the similarity between the result of the present analysis and that
based on the constituent quark models, which predict a more stable pentaquark
states when the antiquark is heavy.Comment: 19 pages, 8 figures, REVTex, revised version,new figures added and
references update
Coulomb corrections to bremsstrahlung in electric field of heavy atom at high energies
The differential and partially integrated cross sections are considered for
bremsstrahlung from high-energy electrons in atomic field with the exact
account of this field. The consideration exploits the quasiclassical electron
Green's function and wave functions in an external electric field. It is shown
that the Coulomb corrections to the differential cross section are very
susceptible to screening. Nevertheless, the Coulomb corrections to the cross
section summed up over the final-electron states are independent of screening
in the leading approximation over a small parameter ( is
a screening radius, is the electron mass, ). Bremsstrahlung from
an electron beam of the finite size on heavy nucleus is considered as well.
Again, the Coulomb corrections to the differential probability are very
susceptible to the beam shape, while those to the probability integrated over
momentum transfer are independent of it, apart from the trivial factor, which
is the electron-beam density at zero impact parameter. For the Coulomb
corrections to the bremsstrahlung spectrum, the next-to-leading terms with
respect to the parameters ( is the electron energy) and
are obtained.Comment: 13 pages, 4 figure
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