202 research outputs found
pi N --> Multi-pi N Scattering in the 1/N_c Expansion
We extend the 1/N_c expansion meson-baryon scattering formalism to cases in
which the final state contains more than two particles. We first show that the
leading-order large N_c processes proceed through resonant intermediate states
(e.g., rho N or pi Delta). We then tabulate linear amplitude expressions for
relevant processes and find that the pole structure of baryon resonances can be
uniquely identified by their (non)appearance in eta N or mixed partial-wave pi
Delta final states. We also show that quantitative predictions of pi N to pi
Delta branching ratios predicted at leading order alone do not agree with
measurements, but the inclusion of 1/N_c corrections is ample to explain the
discrepancies.Comment: 23 pages, 3 eps figures, ReVTeX4, added reference and discussion,
identical to PRD versio
Diabatic Representation of Exotic Hadrons in the Dynamical Diquark Model
We apply the diabatic formalism, an extension of the adiabatic approximation
inherent to the Born-Oppenheimer (BO) approach of atomic physics, to the
problem of mixing between exotic multiquark hadrons and their nearby di-hadron
thresholds. The unperturbed BO eigenstates are obtained using the dynamical
diquark model, while the diabatic calculation introduces a mixing potential
between these states and the threshold states. We solve the resulting coupled
Schr\"{o}dinger equations numerically for hidden-charm tetraquarks of both open
and closed strangeness to obtain physical mass eigenvalues, and explore the
di-hadron state content and spatial extent of the eigenstates. As an explicit
example, emerges with a dominant component, but
also contains a considerable diquark-antidiquark component that can contribute
significantly to its radiative decay widths, and this component also generates
a full multiplet of other diquark-based exotic hadrons to be compared with
experiment.Comment: 9 pages - Version accepted to Physical Review
Pion-Nucleon Scattering Relations at Next-to-Leading Order in 1/N_c
We obtain relations between partial-wave amplitudes for pi-N-->pi-N and
pi-N-->pi-Delta directly from large N_c QCD. While linear relations among
certain amplitudes holding at leading order (LO) in 1/N_c were derived in the
context of chiral soliton models two decades ago, the present work employs a
fully model-independent framework based on consistency with the large N_c
expansion. At LO we reproduce the soliton model results; however, this method
allows for systematic corrections. At next-to-leading order (NLO), most
relations require additional unknown functions beyond those appearing at
leading order (LO) and thus have little additional predictive power. However,
three NLO relations for the pi-N-->pi-Delta reaction are independent of unknown
functions and make predictions accurate at this order. The amplitudes relevant
to two of these relations were previously extracted from experiment. These
relations describe experiment dramatically better than their LO counterparts.Comment: 8 pages, 2 figures; references adde
Pion Photoproduction Amplitude Relations in the 1/N_c Expansion
We derive expressions for pion photoproduction amplitudes in the 1/N_c
expansion of QCD, and obtain linear relations directly from this expansion that
relate electromagnetic multipole amplitudes at all energies. The leading-order
relations in 1/N_c compare favorably with available data, while the
next-to-leading order relations seem to provide only a small improvement.
However, when resonance parameters are compared directly, the agreement at
O(1/N_c) or O(1/N_c^2) is impressive.Comment: 19 pages, ReVTeX, 50 eps files combine into 5 compound figure
SU(3) Clebsch-Gordan Coefficients for Baryon-Meson Coupling at Arbitrary N_c
We present explicit formulae for the SU(3) Clebsch-Gordan coefficients that
are relevant for the couplings of large N_c baryons to mesons. In particular,
we compute the Clebsch-Gordan series for the coupling of the octet (associated
with mesons, and remains the correct representation at large N_c) to the large
N_c analogs of the baryon octet and decuplet representations.Comment: 8 pages, no figures, ReVTe
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