12,715 research outputs found

### An Analysis of \pi\pi-Scattering Phase Shift and Existence of \sigma(555) particle

In most of the Nambu:Jona-Lasinio(NJL)-type models, realizing the hidden
chiral symmetry, the existence of a scalar particle \sigma is needed with a
mass m_\sigma=2 m_q, as a partner of the Nambu-Goldstone boson \pi. However,
the results of many analyses on \pi\pi phase-shift thus far made have been
negative for its existence. In this paper we re-analyze the phase-shift,
applying a new method, the interfering amplitude method, which treats the
T-matrix directly and describes multi-resonances in conformity with the
unitarity. As a result, the existence of \sigma has been strongly suggested
from the behavior of the \pi\pi-->\pi\pi phase shift between the \pi\pi- and
the KK- thresholds, with mass = 553.3 +- 0.5_{st} MeV and width= 242.6 +-
1.2_{st} MeV. The most crucial point in our analysis is the introduction of a
negative background phase, possibly reflecting a ``repulsive core" in \pi\pi
interactions. The properties of f_0(980) are also investigated from data
including those over the KK threshold. Its mass is obtained as 993.2 +-
6.5_{st} +- 6.9_{sys} MeV. Its width is about a hundred MeV, although this
depends largely on the treatment of the elasticity and the \pi\pi-->KK phase
shift, both of which may have large experimental uncertainties.Comment: 22 pages, Latex with Prog. Theor. Phys. format PTPTEX.sty, 4 EPS
figure

### pi^0 pi^0 Scattering Amplitudes and Phase Shifts Obtained by the pi^- P Charge Exchange Process

The results of the analysis of the pi^0 pi^0 scattering amplitudes obtained
with pi^- P charge exchange reaction, pi^- P --> pi^0 pi^0 n, data at 9 GeV/c
are presented. The pi^0 pi^0 scattering amplitudes show clear f_0(1370) and
f_2(1270) signals in the S and D waves, respectively. The pi^0 pi^0 scattering
phase shifts have been obtained below Kbar K threshold and been analyzed by the
Interfering Amplitude method with introduction of negative background phases.
The results show a S wave resonance, sigma. Its Breit-Wigner parameters are in
good agreement with those of our previous analysis on the pi^+ pi^- phase shift
data.Comment: 4 pages, 4 figures. Proceedings of the int. conf. Hadron'99 at
Beijing, Aug. 1999. Presented for the collaboration of A.M.Ma, K.Takamatsu,
M.Y.Ishida, S.Ishida, T.Ishida, T. Tsuru and H. Shimizu, and the E135
collaboration. For our activities on sigma, visit
http://amaterasu.kek.jp/sigm

### Section 337 and National Treatment under GATT: A Proposal for Legislative Reform

This Article discusses the GATT panel reports on Section 337, the U.S. reaction to the GATT findings and possible amendments to Section 337 that would put the United States in compliance with its international obligations. Taking into account the difficult balancing act necessary to change Section 337 the authors attempt to take these requirements into account in suggesting ways out of the quandary in which the United States and its trading partners now find themselves

### Mixing among light scalar mesons and L=1 q\bar{q} scalar mesons

Following the re-establishment of the \sigma(600) and the \kappa(900), the
light scalar mesons a_0(980) and f_0(980) together with the \sigma(600) and the
\kappa(900) are considered as the chiral scalar partner of pseudoscalar nonet
in SU(3) chiral symmetry, and the high mass scalar mesons a_0(1450),
K^*_0(1430), f_0(1370) and f_0(1710) turned out to be considered as the L=1
q\bar{q} scalar mesons. We assume that the high mass of the L=1 q\bar{q} scalar
mesons is caused by the mixing with the light scalar mesons. For the structure
of the light scalar mesons, we adopted the qq\bar{q}\bar{q} model in order to
explain the "scalar meson puzzle". The inter-mixing between the light scalar
nonet and the high mass L=1 q\bar{q} nonet and the intra-mixing among each
nonet are analyzed by including the glueball into the high mass scalar nonet.Comment: 16 pages, 5 figure

### Embedding approach for dynamical mean field theory of strongly correlated heterostructures

We present an embedding approach based on localized basis functions which
permits an efficient application of the dynamical mean field theory (DMFT) to
inhomogeneous correlated materials, such as semi-infinite surfaces and
heterostructures. In this scheme, the semi-infinite substrate leads connected
to both sides of the central region of interest are represented via complex,
energy-dependent embedding potentials that incorporate one-electron as well as
many-body effects within the substrates. As a result, the number of layers
which must be treated explicitly in the layer-coupled DMFT equation is greatly
reduced. To illustrate the usefulness of this approach, we present numerical
results for strongly correlated surfaces, interfaces, and heterostructures of
the single-band Hubbard model.Comment: 8 pages, 4 figures; typos correcte

### Nonlinear optical response of wave packets on quantized potential energy surfaces

We calculated the dynamics of nuclear wave packets in coupled
electron-vibration systems and their nonlinear optical responses. We found that
the quantized nature of the vibrational modes is observed in pump-probe spectra
particularly in weakly interacting electron-vibration systems such as cyanine
dye molecules. Calculated results based on a harmonic potential model and
molecular orbital calculations are compared with experimental results, and we
also found that the materials parameters regarding with the geometrical
structure of potential energy surfaces are directly determined by accurate
measurement of time-resolved spectra.Comment: 19 pages, 6 figures, 1 tabl

### On the nature of light scalar mesons from their large $N_c$ behavior

We show how to obtain information about the states of an effective field
theory in terms of the underlying fundamental theory. In particular we analyze
the spectroscopic nature of meson resonances from the meson-meson scattering
amplitudes of the QCD low energy effective theory, combined with the expansion
in the large number of colors. The vectors follow a qqbar behavior, whereas the
sigma, kappa and f_0(980) scalars disappear for large N_c, in support of a
qqqbarqbar-like nature. The a_0 shows a similar pattern, but the uncertainties
are large enough to accommodate both interpretations.Comment: 4 pages. Slightly shortened version to appear in Phys. Rev. Lett. Two
typos correcte

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