340 research outputs found
Forward dispersion relations and Roy equations in pi-pi scattering
We review results of an analysis of pipi interactions in S, P and D waves for
two-pion effective mass from threshold to about 1.4 GeV. In particular we show
a recent improvement of this analysis above the K anti-K threshold using more
data for phase shifts and including the S0 wave inelasticity from pipi -> K
anti-K. In addition, we have improved the fit to the f2(1270) resonance and
used a more flexible P wave parametrization above the K anti-K threshold and
included an estimation of the D2 wave inelasticity. The better accuracy thus
achieved also required a refinement of the Regge analysis above 1.42 GeV. We
have checked that the pipi scattering amplitudes obtained in this approach
satisfy remarkably well forward dispersion relations and Roy's equations.Comment: 6 pages, invited talk to the IV International Conference on Quarks
and Nuclear Physics QNP06, Madrid 5th-10th June 200
Widespread HCN maser emission in carbon-rich evolved stars
Context. HCN is a major constituent of the circumstellar envelopes of
carbon-rich evolved stars, and rotational lines from within its vibrationally
excited states probe parts of these regions closest to the stellar surface. A
number of such lines are known to show maser action. Historically, in one of
them, the 177 GHz line in the -doubled bending mode has
been found to show relatively strong maser action, with results only published
for a single object, the archetypical high-mass loss asymptotic giant branch
(AGB) star IRC+10216. Aims. To examine how common 177 GHz HCN maser emission
is, we conducted an exploratory survey for this line toward a select sample of
carbon-rich asymptotic giant branch stars that are observable from the southern
hemisphere. Methods. We used the Atacama Pathfinder Experiment 12 meter
submillimeter Telescope (APEX) equipped with a new receiver to simultaneously
observe three HCN rotational transitions, the and -doublet components, and the line from
the (0,0,0) ground state. Results. The maser line is
detected toward 11 of 13 observed sources, which all show emission in the
(0,0,0) transition. In most of the sources, the peak intensity of the
line rivals that of the (0,0,0) line; in two sources,
it is even stronger. Except for the object with the highest mass-loss rate,
IRC+10216, the line covers a smaller velocity range
than the (0,0,0) line. Conclusions. Maser emission in the 177 GHz
line of HCN appears to be common in
carbon-rich AGB stars. (Abbreviated)Comment: 12 pages (including appendix), 3 figures / Astronomy & Astrophysics
(in press
The pion-pion scattering amplitude. II: Improved analysis above threshold
We improve, in the energy region between threshold and
GeV, the energy-dependent phase shift analysis of scattering presented
in a previous paper. For the S0 wave we have included more data above
threshold and we have taken into account systematically the
elasticity data on the reaction . We here made a coupled
channel fit. For the D0 wave we have considered information on low energy
parameters, and imposed a better fit to the resonance. For both waves the
expressions we now find are substantially more precise than the previous ones.
We also provide slightly improved D2 and P waves, including the estimated
inelasticity for the first, and a more flexible parametrization between 1 and
1.42 GeV for the second. The accuracy of our amplitudes is now such that it
requires a refinement of the Regge analysis, for GeV, which
we also carry out. We show that this more realistic input produces
scattering amplitudes that satisfy better forward dispersion relations,
particularly for scattering.Comment: Plain TeX. 12 figures. Minor anomaly in the K-matrix fit corrected by
moving matching point to 932 MeV, and pole to 910.6 MeV. Results
unaltere
The pion-pion scattering amplitude. III: Improving the analysis with forward dispersion relations and Roy equations
We complete and improve the fits to experimental scattering
amplitudes, both at low and high energies, that we performed in the previous
papers of this series. We then verify that the corresponding amplitudes satisfy
analyticity requirements, in the form of partial wave analyticity at low
energies, forward dispersion relations (FDR) at all energies, and Roy equations
below threshold; the first by construction, the last two, inside
experimental errors. Then we repeat the fits including as constraints FDR and
Roy equations. The ensuing central values of the various scattering amplitudes
verify very accurately FDR and, especially, Roy equations, and change very
little from what we found by just fitting data, with the exception of the D2
wave phase shift, for which one parameter moves by . These improved
parametrizations therefore provide a reliable representation of pion-pion
amplitudes with which one can test various physical relations. We also present
a list of low energy parameters and other observables. In particular, we find
,
and .Comment: Plain TeX. 29 figures. Version to be published in PRD, with improved
P and F wave
Precise dispersive data analysis of the f0(600) pole
We review how the use of recent precise data on kaon decays together with
forward dispersion relations (FDR) and Roy's equations allow us to determine
the sigma resonance pole position very precisely, by using only experimental
input. In addition, we present preliminary results for a modified set of
Roy-like equations with only one subtraction, that show a remarkable
improvement in the precision around the sigma region. We also improve the
matching between the parametrizations at low and intermediate energy of the S0
wave, and show that the effect of this on the sigma pole position is
negligible.Comment: 4 pages, 1 figure. To appear in the proceedings of the Meson 2008
conference, June 6-10, Cracow, Polan
Eikonal perturbation theory in photoionization
The eikonal perturbation theory is formulated and applied to photoionization by strong laser pulses. A special emphasis is put on the first order approximation with respect to the binding potential, which is known as the generalized eikonal approximation [2015 Phys. Rev. A 91 053417]. The ordinary eikonal approximation and its domain of applicability is derived from the generalized eikonal approximation. While the former approach is singular for the electron trajectories which return to the potential center, the generalized eikonal avoids this problem. This property makes it a promising tool for further investigations of rescattering and high-order harmonic generation processes
Vortex Structures and Momentum Sharing in Dynamic Sauter-Schwinger Process
Vortex pattern formation in electron-positron pair creation from vacuum by a
time-dependent electric field of linear polarization is analyzed. It is
demonstrated that in such scenario the momentum distributions of created
particles exhibit vortex-antivortex pairs. Their sensitivity to the laser field
parameters such as the field frequency and intensity is also studied.
Specifically, it is shown that with increasing field frequency accross the
one-photon threshold additional vortex-antivortex pairs appear. Their location
in the momentum space is consistent with a general threshold behavior of
probability distributions of created electrons (positrons). Namely, while for
small field frequencies the particles tend to be created along the field
polarization direction, for large enough frequencies they are predominantly
generated in the perpendicular direction. Such change in longitudinal and
transverse momentum sharing of created particles occurs accross the one-photon
threshold.Comment: This article belongs to the special issue of Acta Physica Polonica A
printed in honor of Professor Iwo Bialynicki-Birula on the occasion of his
90th birthday (Ed. Tomasz Sowinski, DOI:10.12693/APhysPolA.143.S0
Masses and widths of scalar-isoscalar multi-channel resonances from data analysis
Peculiarities of obtaining parameters for broad multi-channel resonances from
data are discussed analyzing the experimental data on processes
in the channel in a
model-independent approach based on analyticity and unitarity and using an
uniformization procedure. We show that it is possible to obtain a good
description of the scattering data from the threshold to 1.89 GeV with
parameters of resonances cited in the PDG tables as preferred. However, in this
case, first, representation of the background is unsatisfactory;
second, the data on the coupled process are not well
described even qualitatively above 1.15 GeV when using the resonance parameters
from the only scattering analysis. The combined analysis of these
coupled processes is needed, which is carried out satisfactorily. Then both
above-indicated flaws, related to the analysis of solely the
-scattering, are cured. The most remarkable change of parameters with
respect to the values of only scattering analysis appears for the mass
of the which is now in some accordance with the Weinberg prediction
on the basis of mended symmetry and with an analysis using the large-
consistency conditions between the unitarization and resonance saturation. The
obtained -scattering length in case when we restrict to the
analysis of the scattering or consider so-called A-solution (with a
lower mass and width of meson) agrees well with prediction of chiral
perturbation theory (ChPT) and with data extracted at CERN by the NA48/2
Collaboration from the analysis of the decay and by the DIRAC
Collaboration from the measurement of the lifetime.Comment: 21 pages, 3 figures, 6 table
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