502 research outputs found
Computing the Loewner driving process of random curves in the half plane
We simulate several models of random curves in the half plane and numerically
compute their stochastic driving process (as given by the Loewner equation).
Our models include models whose scaling limit is the Schramm-Loewner evolution
(SLE) and models for which it is not. We study several tests of whether the
driving process is Brownian motion. We find that just testing the normality of
the process at a fixed time is not effective at determining if the process is
Brownian motion. Tests that involve the independence of the increments of
Brownian motion are much more effective. We also study the zipper algorithm for
numerically computing the driving function of a simple curve. We give an
implementation of this algorithm which runs in a time O(N^1.35) rather than the
usual O(N^2), where N is the number of points on the curve.Comment: 20 pages, 4 figures. Changes to second version: added new paragraph
to conclusion section; improved figures cosmeticall
Chiral corrections to kaon-nucleon scattering lengths
We calculate the threshold T-matrices of kaon-nucleon and antikaon-nucleon
scattering to one loop order in SU(3) heavy baryon chiral perturbation theory.
To that order the complex-valued isospin-1 threshold T-matrix can be
successfully predicted from the isospin-0 and 1 threshold T-matrices. As
expected perturbation theory fails to explain the isospin-0 threshold
T-matrix which is completely dominated by the nearby subthreshold
-resonance. Cancelations of large terms of second and third
chiral order are observed as they seem to be typical for SU(3) baryon chiral
perturbation theory calculations. We also give the kaon and eta loop
corrections to the scattering lengths and we investigate
scattering to one-loop order. The second order s-wave low-energy constants are
all of natural size and do not exceed 1 GeV in magnitude.Comment: 8 pages, 2 figures, published in Phys. Rev. C64, 045204 (2001),
corrections of numerical prefactors in Eqs.(10,11,12
NASA Platform for Autonomous Systems (NPAS)
NASA Platform for Autonomous Systems (NPAS) is a disruptive software platform and processes being developed by SSC Autonomous Systems Laboratory (ASL). Autonomous operations are critical for the success, safety and crew survival of NASA deep space missions beyond low Earth orbit, including Lunar Orbital Platform-Gateway, and for the future of cost-effective ground mission operations. NPAS represents the embodiment of an innovative implementation for "thinking" autonomy in contrast to brute-force autonomy. It also uniquely addresses the requirements and integrates five primary functionalities for autonomous operations including: (1) Integrated System Health Management (ISHM), (2) autonomy, guided by health and system concepts of operations; (3) knowledge models of applications; (4) infrastructure to create, schedule, and execute mission plans; and (5) infrastructure to integrate distributed autonomous applications across networks
Spectral functions of isoscalar scalar and isovector electromagnetic form factors of the nucleon at two-loop order
We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
and Im at the two-pion threshold
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at . In the
case of the scalar spectral function Im one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological -meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.Comment: 10 pages, 6 figures, submitted to Physical Review
Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector
We study the S-wave interaction of mesons with baryons in the strangeness S=0
sector in a coupled channel unitary approach. The basic dynamics is drawn from
the lowest order meson baryon chiral Lagrangians. Small modifications inspired
by models with explicit vector meson exchange in the t-channel are also
considered. In addition the pi pi N channel is included and shown to have an
important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure
Axial vector form factor of nucleons in a light-cone diquark model
The nucleon axial vector form factor is investigated in a light-cone quark
spectator diquark model, in which Melosh rotations are applied to both the
quark and vector diquark. It is found that this model gives a very good
description of available experimental data and the results have very little
dependence on the parameters of the model. The relation between the nucleon
axial constant and the anomalous magnetic moment of nucleons is also discussed.Comment: 8 pages, Revtex4, 1 figure, version to be published in Phys. Rev.
Femto-Photography of Protons to Nuclei with Deeply Virtual Compton Scattering
Developments in deeply virtual Compton scattering allow the direct
measurements of scattering amplitudes for exchange of a highly virtual photon
with fine spatial resolution. Real-space images of the target can be obtained
from this information. Spatial resolution is determined by the momentum
transfer rather than the wavelength of the detected photon. Quantum photographs
of the proton, nuclei, and other elementary particles with resolution on the
scale of a fraction of a femtometer is feasible with existing experimental
technology.Comment: To be published in Physical Review D. Replaces previous version with
minor changes in presentatio
Chiral dynamics of p-wave in K^- p and coupled states
We perform an evaluation of the p-wave amplitudes of meson-baryon scattering
in the strangeness S=-1 sector starting from the lowest order chiral
Lagrangians and introducing explicitly the Sigma^* field with couplings to the
meson-baryon states obtained using SU(6) symmetry. The N/D method of
unitarization is used, equivalent, in practice, to the use of the
Bethe-Salpeter equation with a cut-off. The procedure leaves no freedom for the
p-waves once the s-waves are fixed and thus one obtains genuine predictions for
the p-wave scattering amplitudes, which are in good agreement with experimental
results for differential cross sections, as well as for the width and partial
decay widths of the Sigma^*(1385).Comment: LaTeX, 18 pages, 6 figure
Lattice calculations for A=3,4,6,12 nuclei using chiral effective field theory
We present lattice calculations for the ground state energies of tritium,
helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our results were
previously summarized in a letter publication. This paper provides full details
of the calculations. We include isospin-breaking, Coulomb effects, and
interactions up to next-to-next-to-leading order in chiral effective field
theory.Comment: 38 pages, 11 figures, final publication versio
Rare charm meson decays D->Pl^+l^- and c->ul^+l^- in SM and MSSM
We study the nine possible rare charm meson decays D->Pl^+l^-
(P=pi,K,eta,eta') using the Heavy Meson Chiral Lagrangians and find them to be
dominated by the long distance contributions. The decay D^+ -> pi^+l^+l^- with
the branching ratio 1*10^(-6) is expected to have the best chances for an early
experimental discovery. The short distance contribution in the five Cabibbo
suppressed channels arises via the c->ul^+l^- transition; we find that this
contribution is detectable only in the D->pi l^+l^- decay, where it dominates
the differential spectrum at high-q^2. The general Minimal Supersymmetric
Standard Model can enhance the c->ul^+l^- rate by up to an order of magnitude;
its effect on the D->Pl^+l^- rates is small since the c->ul^+l^- enhancement is
sizable in low-q^2 region, which is inhibited in the hadronic decay.Comment: 17 page
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