242 research outputs found
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
Views of the Chiral Magnetic Effect
My personal views of the Chiral Magnetic Effect are presented, which starts
with a story about how we came up with the electric-current formula and
continues to unsettled subtleties in the formula. There are desirable features
in the formula of the Chiral Magnetic Effect but some considerations would lead
us to even more questions than elucidations. The interpretation of the produced
current is indeed very non-trivial and it involves a lot of confusions that
have not been resolved.Comment: 19 pages, no figure; typos corrected, references significantly
updated, to appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
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
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
Examining Periodic Solar Wind Density Structures Observed in the SECCHI Heliospheric Imagers
We present an analysis of small-scale, periodic, solar-wind density
enhancements (length-scales as small as \approx 1000 Mm) observed in images
from the Heliospheric Imager (HI) aboard STEREO A. We discuss their possible
relationship to periodic fluctuations of the proton density that have been
identified at 1 AU using in-situ plasma measurements. Specifically, Viall,
Kepko, and Spence (2008) examined 11 years of in-situ solar-wind density
measurements at 1 AU and demonstrated that not only turbulent structures, but
also non-turbulent periodic density structures exist in the solar wind with
scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall,
Spence, and Kasper (2009) analyzed the {\alpha} to proton solar-wind abundance
ratio measured during one such event of periodic density structures,
demonstrating that the plasma behavior was highly suggestive that either
temporally or spatially varying coronal source plasma created those density
structures. Large periodic density structures observed at 1 AU, which were
generated in the corona, can be observable in coronal and heliospheric
white-light images if they possess sufficiently high density contrast. Indeed,
we identify such periodic density structures as they enter the HI field of view
and follow them as they advect with the solar wind through the images. The
smaller periodic density structures that we identify in the images are
comparable in size to the larger structures analyzed in-situ at 1 AU, yielding
further evidence that periodic density enhancements are a consequence of
coronal activity as the solar wind is formed.Comment: 15 pages, 12 figures. The final publication is available at
http://www.springerlink.co
Denominators of Eisenstein cohomology classes for GL_2 over imaginary quadratic fields
We study the arithmetic of Eisenstein cohomology classes (in the sense of G.
Harder) for symmetric spaces associated to GL_2 over imaginary quadratic
fields. We prove in many cases a lower bound on their denominator in terms of a
special L-value of a Hecke character providing evidence for a conjecture of
Harder that the denominator is given by this L-value. We also prove under some
additional assumptions that the restriction of the classes to the boundary of
the Borel-Serre compactification of the spaces is integral. Such classes are
interesting for their use in congruences with cuspidal classes to prove
connections between the special L-value and the size of the Selmer group of the
Hecke character.Comment: 37 pages; strengthened integrality result (Proposition 16), corrected
statement of Theorem 3, and revised introductio
CP Violation in Hyperon Nonleptonic Decays within the Standard Model
We calculate the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in
nonleptonic hyperon decay within the Standard Model using the framework of
heavy-baryon chiral perturbation theory (chiPT). We identify those terms that
correspond to previous calculations and discover several errors in the existing
literature. We present a new result for the lowest-order (in chiPT)
contribution of the penguin operator to these asymmetries, as well as an
estimate for the uncertainty of our result that is based on the calculation of
the leading nonanalytic corrections.Comment: 21 pages, 2 figures; discussion clarified, results & conclusions
unchanged, to appear in Phys. Rev.
Parity Violation in Proton-Proton Scattering at 221 MeV
TRIUMF experiment 497 has measured the parity violating longitudinal
analyzing power, A_z, in pp elastic scattering at 221.3 MeV incident proton
energy. This paper includes details of the corrections, some of magnitude
comparable to A_z itself, required to arrive at the final result. The largest
correction was for the effects of first moments of transverse polarization. The
addition of the result, A_z=(0.84 \pm 0.29 (stat.) \pm 0.17 (syst.)) \times
10^{-7}, to the pp parity violation experimental data base greatly improves the
experimental constraints on the weak meson-nucleon coupling constants
h^{pp}_\rho and h^{pp}_\omega, and has implications for the interpretation of
electron parity violation experiments.Comment: 17 pages RevTeX, 14 PostScript figures. Revised version with
additions suggested by Phys. Rev.
TomograPy: A Fast, Instrument-Independent, Solar Tomography Software
Solar tomography has progressed rapidly in recent years thanks to the
development of robust algorithms and the availability of more powerful
computers. It can today provide crucial insights in solving issues related to
the line-of-sight integration present in the data of solar imagers and
coronagraphs. However, there remain challenges such as the increase of the
available volume of data, the handling of the temporal evolution of the
observed structures, and the heterogeneity of the data in multi-spacecraft
studies.
We present a generic software package that can perform fast tomographic
inversions that scales linearly with the number of measurements, linearly with
the length of the reconstruction cube (and not the number of voxels) and
linearly with the number of cores and can use data from different sources and
with a variety of physical models: TomograPy
(http://nbarbey.github.com/TomograPy/), an open-source software freely
available on the Python Package Index. For performance, TomograPy uses a
parallelized-projection algorithm. It relies on the World Coordinate System
standard to manage various data sources. A variety of inversion algorithms are
provided to perform the tomographic-map estimation. A test suite is provided
along with the code to ensure software quality. Since it makes use of the
Siddon algorithm it is restricted to rectangular parallelepiped voxels but the
spherical geometry of the corona can be handled through proper use of priors.
We describe the main features of the code and show three practical examples
of multi-spacecraft tomographic inversions using STEREO/EUVI and STEREO/COR1
data. Static and smoothly varying temporal evolution models are presented.Comment: 21 pages, 6 figures, 5 table
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