7 research outputs found
Pion-Pion Phase-Shifts and the Value of Quark-Antiquark Condensate in the Chiral Limit
We use low energy pion-pion phase-shifts in order to make distinction between
the alternatives for the value of the quark-antiquark condensate in the
chiral limit. We will consider the amplitude up to and including contributions within the Standard and Generalized Chiral Perturbation
Theory frameworks. They are unitarized by means of Pad\'e approximants in order
to fit experimental phase-shifts in the resonance region. As the best fits
correspond to , we conclude that pion-pion phase-shift
analysis favors the standard ChPT scenario, which assumes just one, large
leading order parameter .Comment: 5 pages, 3 figures and 1 tabl
Crossing Symmetry Violation of Unitarized Pion-Pion Amplitude in the Resonance Region
Pion-pion scattering amplitude obtained from one-loop Chiral Perturbation
Theory (ChPT) is crossing symmetric, however the corresponding partial wave
amplitudes do not respect exact unitarity relation. There are different
approaches to get unitarized partial wave amplitudes from ChPT. Here we
consider the inverse amplitude method (IAM) that is often used to fit pion-pion
phase shifts to experimental data, by adjusting free parameters. We measure the
amount of crossing symmetry violation (CSV) in this case and we show that
crossing symmetry is badly violated by the IAM unitarized ChPT amplitude in the
resonance region. Important CSV also occurs when all free parameters are set
equal to zero.Comment: 6 pages, 4 figure
Theoretical Study of the \gamma\gamma-->meson-meson Reaction
We present a unified picture which studies simultaneously the gamma
gamma-->pi^+ pi^-, pi^0 pi^0, K^+ K^-, K^0 bar{K}^0, pi^0 eta reactions up to
about sqrt(s)=1.4 GeV reproducing the experimental cross sections. The present
work implements in an accurate way the final state interactions of the
meson-meson system, which is shown to be essential in order to reproduce the
data, particularly the L=0 channel. This latter channel is treated here
following a recent theoretical work in which the meson-meson amplitudes are
well reproduced and the f_0, a_0, sigma resonances show up clearly as poles of
the t matrix. The present work, as done in earlier ones, also incorporates
elements of chiral symmetry and exchange of vector and axial resonances in the
crossed channels, as well as a direct coupling to the f_2(1270) and a_2(1320)
resonances. We also evaluate the decay width of the f_0(980) and a_0(980)
resonances into the gamma-gamma channel.Comment: 20 pages, 13 figures, LaTeX. Only significant change in the
calculation of \gamma\gamma-->pi^+ pi^- from the more careful treatment of
the tail of the f_2(1270) resonanc
Outcomes of inpatient mobilization: a literature review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106977/1/jocn12315.pd