1,700 research outputs found
Diquarks and antiquarks in exotics: a menage a trois and a menage a quatre
A menage a trois is very different from an ordinary family. Similarly, exotic
hadrons with both qq and qbar q pairs have important color-space correlations
that are completely absent in ordinary mesons and baryons. The presence of both
types of pairs requires attention to the basic QCD physics that the q qbar
interaction is much stronger than the qq interaction. This new physics in
multiquark systems produces color structures totally different from those of
normal hadrons, for example the ud system is utterly unlike the ud diquark in
the uds Lambda baryon. The color-space correlations produce unusual
experimental properties in tetraquarks with heavy quark pairs which may be
relevant for newly discovered mesons like the X(3872) resonance. Tetraquark
masses can be below the two-meson threshold for sufficiently high quark masses.
A simple model calculation shows the b q bbar ubar and b q cbar qbar
tetraquarks below the B Bbar and B Dbar thresholds. Some of these states have
exotic electric charge and their decays might have striking signatures
involving monoenergetic photons and/or pions.Comment: Journal version (PLB
A Diquark-Triquark Model for the KN Pentaquark
We propose a model for the recently discovered Theta^+ exotic KN resonance as
a novel kind of a pentaquark with an unusual color structure: a color triplet
(ud) diquark, coupled to a color anti-triplet (ud s-bar) triquark in a relative
P-wave. The state has J^P=1/2^+, I=0 and is an antidecuplet of SU(3)_f. A rough
mass estimate of this pentaquark is close to experiment.Comment: A condensed and amended version of hep-ph/0307243, as published in
PLB, to include pentaquark analysis only, with a revised title and some
additional discussion of the Xi states in the 10-ba
On Reconciling Gottfried Sum Rule Violation with Cabibbo Theory
We discuss the seemingly contradictory constraints of simultaneously
preserving the SU(3)-symmetric Cabibbo description of the weak vector baryon
matrix elements, accounting for SU(3) flavor symmetry breaking and describing
the observed violation of the Gottfried Sum Rule. We try to construct a simple
model that will satisfy these constraints and use it to explain the generic
difficulties and tradeoffs.Comment: 10 pages, late
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