970 research outputs found
Quark Model Explanation of the Branching Ratios
The constituent quark model can explain the strong selectivity of the
decay branching ratios of the nucleon resonances if the fine structure
interaction between the constituent quarks is described in terms of Goldstone
boson exchange. This chiral quark model predicts that the resonances ,
, , , which have mixed flavor and spin
symmetry wavefunctions in lowest order, should have
large branching ratios, while decay of the other resonances
that have different flavor-spin symmetry should be strongly suppressed in
agreement with the experimental branching ratios.Comment: Latex 7 p, no figure
Chiral symmetry restoration and the string picture of hadrons
QCD string picture of highly excited hadrons very naturally explains parity
doubling once the chiral symmetry is restored high in the spectrum. In
particular, the spin-orbit and tensor interactions of quarks at the ends of the
string, related to dynamics of the string, vanish. High in the spectrum there
appears higher degree of degeneracy, namely parity doublets with different
angular momentum cluster around energy of the string in the given quantum
state.Comment: 7 pages, LaTeX, 2 figs. The paper has been further expanded in order
to make the point and physics more clear. To appear in Phys. Lett.
Chiral multiplets of excited mesons
It is shown that experimental meson states with spins J=0,1,2,3 in the energy
range 1.9 - 2.4 GeV obtained in recent partial wave analysis of
proton-antiproton annihilation at LEAR remarkably confirm all predictions of
chiral symmetry restoration. Classification of excited mesons
according to the representations of chiral group is
performed. There are two important predictions of chiral symmetry restoration
in highly excited mesons: (i) physical states must fill out approximately
degenerate parity-chiral multiplets; (ii) some of the physical states with the
given are members of one parity-chiral multiplet, while the other
states with the same are members of the other parity-chiral
multiplet. For example, while some of the excited states are
systematically degenerate with states forming (0,1)+(1,0)
chiral multiplets, the other excited states are degenerate
with states ((1/2,1/2) chiral multiplets). Hence, one of the
predictions of chiral symmetry restoration is that the combined amount of
and states must coincide with the amount of
states in the chirally restored regime. It is shown that the
same rule applies (and experimentally confirmed) to many other meson states.Comment: 14 pages, discussion and conclusion section is largely extende
Effective chiral restoration in the hadronic spectrum and QCD
Effective chiral restoration in the hadronic spectrum has been conjectured as
an explanation of multiplets of nearly degenerate seen in highly excited
hadrons. The conjecture depends on the states being insensitive to the dynamics
of spontaneous chiral symmetry breaking. A key question is whether this concept
is well defined in QCD. This paper shows that it is by means of an explicit
formal construction. This construction allows one to characterize this
sensitivity for any observable calculable in QCD in Euclidean space via a
functional integral. The construction depends on a generalization of the
Banks-Casher theorem. It exploits the fact that {\it all} dynamics sensitive to
spontaneous chiral symmetry breaking observables in correlation functions arise
from fermion modes of zero virtuality (in the infinite volume limit), while
such modes make {\it no} contribution to any of the dynamics which preserves
chiral symmetry. In principle this construction can be implemented in lattice
QCD. The prospect of a practical lattice implementation yielding a direct
numerical test of the concept of effective chiral restoration is discussed
Chiral symmetry restoration in hadron spectra
The evidence and the theoretical justification of chiral symmetry restoration
in high-lying hadrons is presented.Comment: Invited talk given at Int. School on Nuclear Physics "Quarks in
Hadrons and Nuclei", September 2002, Erice/Sicily/Italy; to appear in Progr.
Part. Nucl. Phys., vol. 50; 10 page
Can low-lying Roper states be explained as antidecuplet members?
It is shown that the anomalously low-lying Roper states cannot be assigned as
pentaquarks with the scalar diquark - scalar diquark - antiquark structure as
suggested by Jaffe and Wilczek.Comment: Will appear in Phys. Rev. Lett. as a comment on the paper by R. Jaffe
and F. Wilczek, Phys. Rev. Lett., 91, 232003 (2003
Baryon Spectrum and Chiral Dynamics
New results on baryon structure and spectrum developed in collaboration with
Dan Riska [1-4] are reported. The main idea is that beyond the chiral symmetry
spontaneous breaking scale light and strange baryons should be considered as
systems of three constituent quarks with an effective confining interaction and
a chiral interaction that is mediated by the octet of Goldstone bosons
(pseudoscalar mesons) between the constituent quarks.Comment: 12 pages + 1 fig., LaTeX, fig. is available from author, to appear in
Proceedings of the Int. School of Nucl. Physics: Quarks in Hadrons and Nuclei
(Erice, 19-27 September, 1995) - Progr. Part. Nucl. Phys., v. 36 (1996
Chiral symmetry breaking and the spin content of hadrons
From the parton distributions in the infinite momentum frame one finds that
only about 30% of the nucleon spin is carried by spins of the valence quarks,
which gave rise to the term "spin crisis". Similar results hold for the lowest
mesons, as it follows from the lattice simulations. We define the spin content
of a meson in the rest frame and use a complete and orthogonal
chiral basis and a unitary transformation from the chiral basis to the (2S+1)LJ
basis. Then, given a mixture of different allowed chiral representations in the
meson wave function at a given resolution scale, one can obtain its spin
content at this scale. To obtain the mixture of the chiral representations in
the meson we measure in dynamical lattice simulations a ratio of couplings of
interpolarors with different chiral structure. For the rho meson we obtain
practically the 3S1 state with no trace of the spin crisis. Then a natural
question arises: which definition does reflect the spin content of a hadron?Comment: 7 pp, Presented at Int. School of Nuclear Physics: "From Quarks and
Gluons to Hadrons and Nuclei", Erice-Sicily, 16 - 24 September, 201
Why the high lying glueball does not mix with the neighbouring
Chiral symmetry restoration in high-lying hadron spectra implies that hadrons
which belong to different irreducible representations of the parity-chiral
group cannot mix. This explains why the , which was suggested
to be a glueball, and hence must belong to the scalar (0,0) representation of
the chiral group, cannot mix with the neighbouring , which
was interpreted as a state, and that belongs to the
representation of the chiral group. If confirmed, then we have an access to a
"true" glueball of QCD.Comment: 4 pages, LaTeX, final version, Eur. Phys. J. A 19 (2004) 15
Why the OZI rule is so strongly violated in J/Psi decays?
The new meson recently observed by BES collaboration in
-decay, is seen only in the OZI-forbidden channel. It is shown that
chiral symmetry restoration in excited hadrons implies a new selection rule of
dynamical origin that forbids some of the OZI-favoured mechanisms of decays.
Hence decays into channels that are suppressed by OZI can become dominant.Comment: 5 pages, 5 figures. The paper has been expanded. A new figure as well
as implications of chiral symmetry for the search of missing a_0 mesons in
charmonium decays have been added. To appear in Phys. Rev.
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