1,748 research outputs found

    Meson-Baryon s-wave Resonances with Strangeness -3

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    Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the s-wave meson-baryon resonances in the strangeness S=-3 and negative parity sector. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2+ octet of the nucleon and the 3/2+ decuplet of the Delta. Quantum numbers I(J^P)=0(3/2^-) are suggested for the experimental resonances Omega*(2250)- and Omega*(2380)-. Among other, resonances with I=1 are found, with minimal quark content sss\bar{l}l', being s the strange quark and l, l' any of the the light up or down quarks. A clear signal for such a pentaquark would be a baryonic resonance with strangeness -3 and electric charge of -2 or 0, in proton charge units. We suggest looking for K- Xi- resonances with masses around 2100 and 2240 MeV in the sector 1(1/2^-), and for pi Omega- and K- Xi*- resonances with masses around 2260 MeV in the sector 1(3/2^-).Comment: 3 pages, 1 Postscript figure, 7 table

    SU(6)⊃\supsetSU(3)xSU(2) and SU(8)⊃\supsetSU(4)xSU(2) Clebsch-Gordan coefficients

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    Tables of scalar factors are presented for 63x63 and 120x63 in SU(8)⊃\supsetSU(4)xSU(2), and for 35x35 and 56x35 in SU(6)⊃\supsetSU(3)xSU(2). Related tables for SU(4)⊃\supsetSU(3)xU(1) and SU(3)⊃\supsetSU(2)xU(1) are also provided so that the Clebsch-Gordan coefficients can be completely reconstructed. These are suitable to study meson-meson and baryon-meson within a spin-flavor symmetric scheme.Comment: 30 pages, mostly table

    Resonances and the Weinberg--Tomozawa 56-baryon --35-meson interaction

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    Vector meson degrees of freedom are incorporated into the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which relies on spin--flavor SU(6) symmetry. The corresponding Bethe-Salpeter approximation successfully reproduces previous SU(3)--flavor WT results for the lowest-lying s--wave negative parity baryon resonances, and it also provides some information on the dynamics of the heavier ones. Moreover, it also predicts the existence of an isoscalar spin-parity 32−\frac32^- K∗NK^*N bound state (strangeness +1) with a mass around 1.7--1.8 GeV, unstable through K∗K^* decay. Neglecting d-wave KN decays, this state turns out to be quite narrow (Γ≀15\Gamma \le 15 MeV) and it might provide clear signals in reactions like Îłp→Kˉ0pK+π−\gamma p \to \bar K^0 p K^+\pi^- by looking at the three body pK+π−p K^+\pi^- invariant mass.Comment: Talk given at the IVth International Conference on Quarks an Nuclear Physics, Madrid, June 5th-10th 2006. Minor correction

    Large Nc Weinberg-Tomozawa interaction and negative parity s--wave baryon resonances

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    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 O(Nc0){\cal O}(N_c^0), instead of the well known O(Nc−1){\cal O}(N_c^{-1}) behavior for its SU(3) counterpart. However, the WT interaction behaves as order O(Nc−1){\cal O}(N_c^{-1}) within the 56 and 1134 meson-baryon spaces. Explicit expressions for the WT couplings (eigenvalues) in the irreducible SU(2NFN_F) spaces, for arbitrary NFN_F and NcN_c, are given. This extended interaction is used as a kernel of the Bethe-Salpeter equation, to study the large NcN_c scaling of masses and widths of the lowest--lying negative parity s-wave baryon resonances. Analytical expressions are found in the Nc→∞N_c\to \infty limit, from which it can be deduced that resonance widths and excitation energies (MR−M)(M_R-M) behave as order O(Nc0){\cal O} (N^0_c), 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 O(Nc1/2){\cal O} (N_c^{1/2}) indicating that such resonances do not survive in the large NcN_c limit. The relation of this latter NcN_c 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

    Exotic dynamically generated baryons with C=−=-1

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    We follow a model based on the SU(8) symmetry for the interaction of mesons with baryons. The model treats on an equal footing the pseudo-scalars and the vector mesons, as required by heavy quark symmetry. The T-matrix calculated within an unitary scheme in coupled channels has poles which are interpreted as baryonic resonances.Comment: 5 pages. Proceedings for Chiral10 workshop, Valencia, June 21-24 201

    Large NN Weinberg-Tomozawa interaction and spin-flavor symmetry

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    The construction of an extended version of the Weinberg-Tomozawa Lagrangian, in which baryons and mesons form spin-flavor multiplets, is reviewed and some of its properties discussed, for an arbitrary number of colors and flavors. The coefficient tables of spin-flavor irreducible representations related by crossing between the ss-, tt- and uu-channels are explicitly constructed.Comment: 3 pages, no figures. Presented at the IVth International Conference on Quarks and Nuclear Physics, Madrid, June 5th-10th 200

    Odd Parity Light Baryon Resonances

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    We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian within a coupled channel unitary approach in order to calculate the T-matrix for meson-baryon scattering in s-wave. The building blocks of the scheme are the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify poles in this unitary T-matrix and interpret them as resonances. We study here the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and 5/2. Many of the poles generated can be associated with known N, Delta, Sigma, Lambda and Xi resonances with negative parity. We show that most of the low-lying three and four star odd parity baryon resonances with spin 1/2 and 3/2 can be related to multiplets of the spin-flavor symmetry group SU(6). This study allows us to predict the spin-parity of the Xi(1620), Xi(1690), Xi(1950), Xi(2250), Omega(2250) and Omega(2380) resonances, which have not been determined experimentally yet.Comment: New appendix and references adde
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