91,302 research outputs found
Large Nc Weinberg-Tomozawa interaction and negative parity s--wave baryon resonances
It is shown that in the 70 and 700 SU(6) irreducible spaces, the SU(6)
extension of the Weinberg-Tomozawa (WT) s-wave meson-baryon interaction
incorporating vector mesons ({\it hep-ph/0505233}) scales as ,
instead of the well known behavior for its SU(3)
counterpart. However, the WT interaction behaves as order
within the 56 and 1134 meson-baryon spaces. Explicit expressions for the WT
couplings (eigenvalues) in the irreducible SU(2) spaces, for arbitrary
and , are given. This extended interaction is used as a kernel of
the Bethe-Salpeter equation, to study the large scaling of masses and
widths of the lowest--lying negative parity s-wave baryon resonances.
Analytical expressions are found in the limit, from which it
can be deduced that resonance widths and excitation energies behave
as order , in agreement with model independent arguments, and
moreover they fall in the 70-plet, as expected in constituent quark models for
an orbital excitation. For the 56 and 1134 spaces, excitation energies and
widths grow indicating that such resonances do not
survive in the large limit. The relation of this latter behavior
with the existence of exotic components in these resonances is discussed. The
interaction comes out repulsive in the 700.Comment: 21 pages, 3 figures, requires wick.sty and young.sty. Subsection
added. Conclusions revised. To appear in Physical Review
Invariance principles for switched systems with restrictions
In this paper we consider switched nonlinear systems under average dwell time
switching signals, with an otherwise arbitrary compact index set and with
additional constraints in the switchings. We present invariance principles for
these systems and derive by using observability-like notions some convergence
and asymptotic stability criteria. These results enable us to analyze the
stability of solutions of switched systems with both state-dependent
constrained switching and switching whose logic has memory, i.e., the active
subsystem only can switch to a prescribed subset of subsystems.Comment: 29 pages, 2 Appendixe
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