195 research outputs found
Universality of Regge and vibrational trajectories in a semiclassical model
The orbital and radial excitations of light-light mesons are studied in the
framework of the dominantly orbital state description. The equation of motion
is characterized by a relativistic kinematics supplemented by the usual funnel
potential with a mixed scalar and vector confinement. The influence of finite
quark masses and potential parameters on Regge and vibrational trajectories is
discussed. The case of heavy-light mesons is also presented.Comment: 12 page
Bound states in a constituent quark model
We consider the existence of bound systems consisting of two quarks and two
antiquarks () within the framework of a constituent quark model.
The underlying quark dynamics is described by a linear confinement potential
and an effective interaction which has its origin in instanton
effects of QCD. We calculate the spectra and examine the internal structure of
the states found.Comment: 11 pages, needs epsf.st
Strong Two--Body Decays of Light Mesons
In this paper, we present results on strong two-body decay widths of light
mesons calculated in a covariant quark model. The model is based on
the Bethe-Salpeter equation in its instantaneous approximation and has already
been used for computing the complete meson mass spectrum and many electroweak
decay observables. Our approach relies on the use of a phenomenological
confinement potential with an appropriate spinorial Dirac structure and 't
Hooft's instanton--induced interaction as a residual force for pseudoscalar and
scalar mesons. The transition matrix element for the decay of one initial meson
into two final mesons is evaluated in lowest order by considering conventional
decays via quark loops as well as Zweig rule violating instanton--induced
decays generated by the six--quark vertex of 't Hooft's interaction; the latter
mechanism only contributes if all mesons in the decay have zero total angular
momentum. We show that the interference of both decay mechanisms plays an
important role in the description of the partial widths of scalar and
pseudoscalar mesons.Comment: 35 pages, 7 figure
Is there diquark clustering in the nucleon?
It is shown that the instanton-induced interaction in qq pairs, iterated in
t-channel, leads to a meson-exchange interactions between quarks. In this way
one can achieve a simultaneous understanding of low-lying mesons, baryons and
the nuclear force. The discussion is general and does not necessarily rely on
the instanton-induced interaction. Any nonperturbative gluonic interaction
between quarks, which is a source of the dynamical chiral symmetry breaking and
explains the - mass splitting, will imply an effective meson
exchange picture in baryons. Due to the (anti)screening there is a big
difference between the initial 't Hooft interaction and the effective
meson-exchange interaction. It is demonstrated that the effective
meson-exchange interaction, adjusted to the baryon spectrum, does not bind the
scalar diquark and does not induce any significant quark-diquark clustering in
the nucleon because of the nontrivial role played by the Pauli principle.Comment: Final version to appear in Phys. Rev. D; typos have been corrected;
some formulae have been written in a more detailed form; some references have
been update
Low-lying spectrum of the Y-string three-quark potential using hyper-spherical coordinates
We calculate the energies of three-quark states with definite permutation
symmetry (i.e. of SU(6) multiplets) in the N=0,1,2 shells, confined by the
Y-string three-quark potential. The exact Y-string potential consists of one,
so-called three-string term, and three angle-dependent two-string terms. Due to
this technical complication we treat the problem at three increasingly accurate
levels of approximation: 1) the (approximate) three-string potential expanded
to first order in trigonometric functions of hyper-spherical angles; 2) the
(approximate) three-string potential to all orders in the power expansion in
hyper-spherical harmonics, but without taking into account the transition(s) to
two-string potentials; 3) the exact minimal-length string potential to all
orders in power expansion in hyper-spherical harmonics, and taking into account
the transition(s) to two-string potentials. We show the general trend of
improvement %convergence of these approximations: The exact non-perturbative
corrections to the total energy are of the order of one per cent, as compared
with approximation 2), yet the exact energy differences between the
-plets are shifted to 2:2:0.9,
from the Bowler and Tynemouth separation rule 2:2:1, which is obeyed by
approximation 2) at the one per cent level. The precise value of the energy
separation of the first radial excitation ("Roper") -plet
from the -plet depends on the approximation, but does not become
negative, i.e. the "Roper" remains heavier than the odd-parity
-plet in all of our approximations.Comment: 19 pages, 6 figure
Towards resolution of the scalar meson nonet enigma
By the application of a linear mass spectrum to a composite system of both
the pseudoscalar and scalar meson nonets, we find three mass relations for the
masses of the scalar states which suggest the assignment for the
scalar meson nonet: Comment: 16 pages, LaTe
Bohr-Sommerfeld quantization and meson spectroscopy
We use the Bohr-Sommerfeld quantization approach in the context of
constituent quark models. This method provides, for the Cornell potential,
analytical formulae for the energy spectra which closely approximate numerical
exact calculations performed with the Schrodinger or the spinless Salpeter
equations. The Bohr-Sommerfeld quantization procedure can also be used to
calculate other observables such as r.m.s. radius or wave function at the
origin. Asymptotic dependence of these observables on quantum numbers are also
obtained in the case of potentials which behave asymptotically as a power-law.
We discuss the constraints imposed by these formulae on the dynamics of the
quark-antiquark interaction.Comment: 13 page
Baryon spectra with instanton induced forces
Except the vibrational excitations of and mesons, the main features
of spectra of mesons composed of quarks , , and can be quite well
described by a semirelativistic potential model including instanton induced
forces. The spectra of baryons composed of the same quarks is studied using the
same model. The results and the limitations of this approach are described.
Some possible improvements are suggested.Comment: 5 figure
Vector mesons in a relativistic point-form approach
We apply the point form of relativistic quantum mechanics to develop a
Poincare invariant coupled-channel formalism for two-particle systems
interacting via one-particle exchange. This approach takes the exchange
particle explicitly into account and leads to a generalized eigenvalue equation
for the Bakamjian-Thomas type mass operator of the system. The coupling of the
exchange particle is derived from quantum field theory. As an illustrative
example we consider vector mesons within the chiral constituent quark model in
which the hyperfine interaction between the confined quark-antiquark pair is
generated by Goldstone-boson exchange. We study the effect of retardation in
the Goldstone-boson exchange by comparing with the commonly used instantaneous
approximation. As a nice physical feature we find that the problem of a too
large - splitting can nearly be avoided by taking the dynamics of
the exchange meson explicitly into account.Comment: 14 pages, 1 figur
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