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© 2007 The American Physical Society. The authors thank Dr. T. van Cauteren, Dr. F. J. Llanes Estrada, Dr. R.A. Molina, Professor E. Moya de Guerra, Dr. J. Retamosa, and Dr. J.M. Udías for valuable comments. A. R. is supported by the Spanish program ‘‘Juan de la Cierva’’. This work has been partly supported under contracts of Ministerio de Educación y Ciencia (Spain) No. FTN2003-08337-C04-04 and No. FIS2005-00640., We study the low-lying baryon spectrum (up to 2.2 GeV) provided by experiments and different quark models using statistical tools which allow us to postulate the existence of missing levels in spectra. We confirm that the experimental spectrum is compatible with random matrix theory, the paradigmatic model of quantum chaos, and we find that the quark models are more similar to a Poisson distribution, which is not compatible with what should be expected in a correlated spectrum. From our analysis it stems that the spectral fluctuation properties of quark-model spectra are incompatible with experimental data. This result can be used to enlighten the problem of missing resonances., Spanish program ‘‘Juan de la Cierva’’, Ministerio de Educación y Ciencia (Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 The American Physical Society. This work is supported by the Japan-Europe (Spain) Research Cooperation Program of Japan Society for the Promotion of Science (JSPS) and Spanish Council for Scientific Research (CSIC), which enabled E.O. and M.J.V.V. to visit RCNP, Osaka. This work is partly supported by DGICYT Contract Numbers BFM2003-00856, FPA 2000-0956, and BFM 2002-01003 and the E.U. EURIDICE Network Contract No. HPRN-CT-2002 00311., We study the two-meson virtual cloud contribution to the self-energy of the SU(3) antidecuplet, to which the Thet (+) pentaquark is assumed to belong. This is motivated by the large branching ratio of the N(1710) decay into two pions and one nucleon. We derive effective Lagrangians that describe the N(1710) decay into N pi pi with two pions in s or p wave. We obtain increased binding for all members of the antidecuplet and a contribution to the mass splitting between states with different strangeness which is at least 20% of the empirical one. We also provide predictions for three-body decays of the pentaquark antidecuplet., Japan-Europe (Spain) Research Cooperation Program of Japan Society for the Promotion of Science (JSPS, Spanish Council for Scientific Research (CSIC), DGICYT, E.U. EURIDICE Network, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub