2,265 research outputs found
piN scattering and electromagnetic corrections in the perturbative chiral quark model
We apply the perturbative chiral quark model to give predictions for the
electromagnetic O(p^2) low-energy couplings of the ChPT effective Lagrangian
that define the electromagnetic mass shifts of nucleons and first-order (e^2)
radiative corrections to the piN scattering amplitude. We estimate the leading
isospin-breaking correction to the strong energy shift of the pi(-)p atom in
the 1s state, which is relevant for the experiment "Pionic Hydrogen" at PSI.Comment: 12 pages, 2 figure
Relativistic Kinetic Equations for Electromagnetic, Scalar and Pseudoscalar Interactions
We derive the kinetic equations for both the covariant and equal-time Wigner
functions of Dirac particles with electromagnetic, scalar and pseudoscalar
interactions. We emphasize the constraint equations for the spinor components
in the equal-time formulation.Comment: 12 pages, no figures, revte
Axial form factor of the nucleon in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyze
the axial form factor of the nucleon. This chiral quark model is based on an
effective Lagrangian, where baryons are described by relativistic valence
quarks and a perturbative cloud of Goldstone bosons as dictated by chiral
symmetry. We apply the formalism to obtain analytical expressions for the axial
form factor of the nucleon, which is given in terms of fundamental parameters
of low-energy pion-nucleon physics (weak pion decay constant, strong
pion-nucleon form factor) and of only one model parameter (radius of the
nucleonic three-quark core).Comment: 23 pages, 5 figures, accepted for publication in J. Phys.
Expectation values of four-quark operators in pions
The values of four-quark operators averaged over pions are expressed through
those averaged over vacuum. The specific values are obtained in the framework
of the factorization assumption. For the condensates of the light quarks of the
same flavour \bar q\Gamma q\bar q\Gamma q the scalar condensate is shown to be
an order of magnitude larger than the other ones. The condensates containing
the strange quarks \bar q q\bar s s appear to be only about twice smaller than
those of the light quarks. The degeneracy of the ground state in the
Nambu--Jona--Lasinio model is shown explicitly.Comment: 9 pages, no figures, typos correcte
The Standard Model in Strong Fields: Electroweak Radiative Corrections for Highly Charged Ions
Electroweak radiative corrections to the matrix elements are calculated for highly charged hydrogenlike ions. These
matrix elements constitute the basis for the description of the most parity
nonconserving (PNC) processes in atomic physics. The operator
represents the parity nonconserving relativistic effective atomic Hamiltonian
at the tree level. The deviation of these calculations from the calculations
valid for the momentum transfer demonstrates the effect of the strong
field, characterized by the momentum transfer ( is the
electron mass). This allows for a test of the Standard Model in the presence of
strong fields in experiments with highly charged ions.Comment: 27 LaTex page
Detection of interstellar CH_3
Observations with the Short Wavelength Spectrometer (SWS) onboard the {\it
Infrared Space Observatory} (ISO) have led to the first detection of the methyl
radical in the interstellar medium. The branch at 16.5
m and the (0) line at 16.0 m have been unambiguously detected
toward the Galactic center SgrA. The analysis of the measured bands gives a
column density of (8.02.4) cm and an excitation
temperature of K. Gaseous at a similarly low excitation
temperature and are detected for the same line of sight. Using
constraints on the column density obtained from and
visual extinction, the inferred abundance is
. The chemically related
molecule is not detected, but the pure rotational lines of are seen
with the Long Wavelength Spectrometer (LWS). The absolute abundances and the
and ratios are inconsistent with published
pure gas-phase models of dense clouds. The data require a mix of diffuse and
translucent clouds with different densities and extinctions, and/or the
development of translucent models in which gas-grain chemistry, freeze-out and
reactions of with polycyclic aromatic hydrocarbons and solid
aliphatic material are included.Comment: 2 figures. ApJL, Accepte
Semiquantum Chaos in the Double-Well
The new phenomenon of semiquantum chaos is analyzed in a classically regular
double-well oscillator model. Here it arises from a doubling of the number of
effectively classical degrees of freedom, which are nonlinearly coupled in a
Gaussian variational approximation (TDHF) to full quantum mechanics. The
resulting first-order nondissipative autonomous flow system shows energy
dependent transitions between regular behavior and semiquantum chaos, which we
monitor by Poincar\'e sections and a suitable frequency correlation function
related to the density matrix. We discuss the general importance of this new
form of deterministic chaos and point out the necessity to study open
(dissipative) quantum systems, in order to observe it experimentally.Comment: LaTeX, 25 pages plus 7 postscript figures. Replaced figure 3 with a
non-bitmapped versio
Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and two-pair diagrams
Two-meson-exchange nucleon-nucleon potentials are derived where either one or
both nucleons contains a pair vertex. Physically, the meson-pair vertices are
meant to describe in an effective way (part of) the effects of heavy-meson
exchange and meson-nucleon resonances. {}From the point of view of ``duality,''
these two kinds of contribution are roughly equivalent. The various
possibilities for meson pairs coupling to the nucleon are inspired by the
chiral-invariant phenomenological Lagrangians that have appeared in the
literature. The coupling constants are fixed using the linear model.
We show that the inclusion of these two-meson exchanges gives a significant
improvement over a potential model including only the standard one-boson
exchanges.Comment: 21 pages RevTeX, 7 postscript figures; revised version as to appear
in Phys. Rev.
Time-resolved investigation of nanometer scale deformations induced by a high flux x-ray beam
We present results of a time-resolved pump-probe experiment where a Si sample was exposed to an intense 15 keV beam and its surface monitored by measuring the wavefront deformation of a reflected optical laser probe beam. By reconstructing and back propagating the wavefront, the deformed surface can be retrieved for each time step. The dynamics of the heat bump, build-up and relaxation, is followed with a spatial resolution in the nanometer range. The results are interpreted taking into account results of finite element method simulations. Due to its robustness and simplicity this method should find further developments at new x-ray light sources (FEL) or be used to gain understanding on thermo-dynamical behavior of highly excited materials. (C) 2011 Optical Society of Americ
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