231 research outputs found
On Goldstone bosons decoupling from high-lying hadrons
In this paper, we discuss a decoupling of the Goldstone bosons from highly
excited hadrons in relation to the restoration of chiral symmetry in such
hadrons. We use a generalised Nambu-Jona-Lasinio model with the interaction
between quarks in the form of an instantaneous Lorentz-vector confining
potential. This model is known to provide spontaneous breaking of chiral
symmetry in the vacuum via the standard selfenergy loops for valence quarks.
For highly excited hadrons, where the typical momentum of valence quarks is
large, the loop contributions represent only a small correction to the
chiral-invariant classical contributions and asymptotically vanish.
Consequently the chiral symmetry violating Lorentz-scalar dynamical mass of
quarks vanishes. Then the conservation of the axial vector current in the
chiral limit requires, via the Goldberger-Treiman relation, that the valence
quarks decouple from the Goldstone boson. As a consequence, the whole hadron
decouples from the Goldstone boson as well, which implies that its axial
constant also vanishes.Comment: RevTeX4, 21 pages, 5 Postscript figures, uses epsfig.sty, new chapter
with numerical estimates added, to appear in Phys.Rev.
Generalized Weinberg's approach to the a0/f0 case
The problem of whether it is possible to distinguish composite from
elementary particles is studied in the framework of Weinberg's approach. The
possibility to extend this approach to the case of unstable particles in the
presence of inelastic channels is considered. The interplay between the
low-energy scattering data and the admixture of a bare state in the resonance
is discussed, and the implications for the a0(980)/f0(980) case are outlined.Comment: LaTeX2e, 5 pages, 2 figures, to appear in the proceedings of the
HADRON03 conference, Aschaffenburg, Germany. September 2003, typo correcte
On two- and three-body descriptions of hybrid mesons
Hybrid mesons are exotic mesons in which the color field is not in its ground
state. Their understanding deserves interest from a theoretical point of view,
because it is intimately related to nonperturbative aspects of QCD. In this
work, we analyze and compare two different descriptions of hybrid mesons,
namely a two-body system with an excited string, or a three-body
system. In particular, we show that the constituent gluon approach
is equivalent to an effective excited string in the heavy hybrid sector.
Instead of a numerical resolution, we use the auxiliary field technique. It
allows to find simplified analytical mass spectra and wave functions, and still
leads to reliable qualitative predictions. We also investigate the light hybrid
sector, and found a mass for the lightest hybrid meson which is in satisfactory
agreement with lattice QCD and other effective models.Comment: 2 figure
Microscopic derivation of the pion coupling to heavy-light mesons
The Goldberger--Treiman relation for heavy--light systems is derived in the
context of a quark model. As a paradigmatic example, the case of is studied in detail. The fundamental role played by the pion
two-component wave function, in the context of the Salpeter equation, is
emphasized.Comment: 6 pages, 2 figures, version to appear in Phys. Rev.
Light-Quark Vector Meson Spectroscopy
The current situation for vector meson spectroscopy is outlined, and it is
shown that the data are inconsistent with the generally-accepted model for
meson decay. A possible resolution in terms of exotic mesons is given. Although
this resolves some of the issues, fresh theoretical questions are raised.Comment: Plenary talk at HADRON2001, Protvin
QCD string model for hybrid adiabatic potentials
Hybrid adiabatic potentials are considered in the framework of the QCD string
model. The einbein field formalism is applied to obtain the large-distance
behaviour of adiabatic potentials. The calculated excitation curves are shown
to be the result of interplay between potential-type longitudinal and
string-type transverse vibrations. The results are compared with recent lattice
data.Comment: LATEX2e, 10 pages, 4 PS figures. Plenary talk at HADRON2001,
Protvino. Comment adde
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