14,096 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
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Mass Uncertainties of f0(600) and f0(1370) and their Effects on Determination of the Quark and Glueball Admixtures of the I=0 Scalar Mesons
Within a nonlinear chiral Lagrangian framework the correlations between the
quark and glueball admixtures of the isosinglet scalar mesons below 2 GeV and
the current large uncertainties on the mass of the f0(600) and the f0(1370) are
studied. The framework is formulated in terms of two scalar meson nonets (a
two-quark nonet and a four-quark nonet) together with a scalar glueball. It is
shown that while some properties of these states are sensitive to the mass of
f0(600) and f0(1370), several relatively robust conclusions can be made: The
f0(600), the f0(980), and the f0(1370) are admixtures of two and four quark
components, with f0(600) being dominantly a non-strange four-quark state, and
f0(980) and f0(1370) having a dominant two-quark component. Similarly, the
f0(1500) and the f0(1710) have considerable two and four quark admixtures, but
in addition have a large glueball component. For each state, a detailed
analysis providing the numerical estimates of all components is given. It is
also shown that this framework clearly favors the experimental values:
m[f0(600)] < 700 MeV and m[f0(1370)] = 1300-1450 MeV. Moreover, an overall fit
to the available data shows a reciprocal substructure for the f0(600) and the
f0(1370), and a linear correlation between their masses of the form m
[f0(1370)] = 0.29 m[f0(600)] + 1.22 GeV. The scalar glueball mass of 1.5-1.7
GeV is found in this analysis.Comment: placement of figures inside text improved. Content unchange
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
Phase Transition in Hot Pion Matter
The equation of state for the pion gas is analyzed within the third virial
approximation. The second virial coefficient is found from the pion-pion-
scattering data, while the third one is considered as a free parameter. The
proposed model leads to a first-order phase transition from the pion gas to a
more dense phase at the temperature T_pt < 136 MeV. Due to relatively low
temperature this phase transition cannot be related to the deconfinement. This
suggests that a new phase of hadron matter - 'hot pion liquid' - may exist.Comment: 11 pages, Latex, 4 PS-figures. V2: A few misprints are corrected.
Acknowledgments are adde
Effect of Dynamical Coulomb Correlations on the Fermi Surface of Na_0.3CoO_2
The t2g quasi-particle spectra of Na_0.3CoO_2 are calculated within the
dynamical mean field theory. It is shown that as a result of dynamical Coulomb
correlations charge is transfered from the nearly filled e_g' subbands to the
a_1g band, thereby reducing orbital polarization among Co t2g states. Dynamical
correlations therefore stabilize the small e_g' Fermi surface pockets, in
contrast to angle-resolved photoemission data, which do not reveal these
pockets.Comment: 4 pages, to appear in PR
Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB
We examine the superconducting anisotropy
of a metallic high- superconductor MgB by measuring the magnetic
torque of a single crystal. The anisotropy does not depend
sensitively on the applied magnetic field at 10 K. We obtain the anisotropy
parameter . The torque curve shows the sharp
hysteresis peak when the field is applied parallel to the boron layers. This
comes from the intrinsic pinning and is experimental evidence for the
occurrence of superconductivity in the boron layers.Comment: REVTeX 4, To be published in Physical Review
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