The formalism developed recently to study vector meson--vector meson interaction, and applied to the case of $\rho\rho$, is extended to study the interaction of the nonet of vector mesons among themselves. The interaction leads to poles of the scattering matrix corresponding to bound states or resonances. We show that 11 states (either bound or resonant) get dynamically generated in nine strangeness-isospin-spin channels. Five of them can be identified with those reported in the PDG, i.e., the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f'_2(1525)$, and $K^*_2(1430)$. The masses of the latter three tensor states have been used to fine-tune the free parameters of the unitary approach, i.e., the subtraction constants in evaluating the vector meson -vector meson loop functions in the dimensional regularization scheme. The branching ratios of these five dynamically generated states are found to be consistent with data. The existence of the other six states should be taken as predictions to be tested by future experiments.Comment: typos corrected; more discussions; one of the appendix rearrange

The axial vector meson K1(1270) was studied within the chiral unitary approach, where it was shown that it has a two-pole structure. We reanalyze the high-statistics WA3 experiment K − p → K − π + π − p at 63 GeV, which established the existence of both K1(1270) and K1(1400), and we show that it clearly favors our two-pole interpretation. We also reanalyze the traditional K-matrix interpretation of the WA3 data and find that the good fit of the data obtained there comes from large cancellations of terms of unclear physical interpretation.

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We calculate the baryon magnetic moments using covariant Chiral Perturbation Theory (χPT) within the Extended-on-mass-shell (EOMS) renormalization scheme. By fitting the two available low-energy constants (LECs), we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using Heavy Baryon (HB) χPT and covariant Infrared (IR) χPT. We also analyze the source of this improvement with particular attention on the comparison between the covariant results. PACS numbers: 12.39.Fe, 14.20.Dh, 14.20.Jn,13.40.Em In the limit that SU(3) is an exact flavour symmetry it is possible to relate the magnetic moments of the baryon-octet and the ΛΣ 0 transition to those of the proton and the neutron. These are the celebrated Coleman-Glashow formulas [1]. The improvement of this description requires the inclusion of a realistic SU(3)-breaking mechanism. Chiral Perturbation Theory (χPT), as the realization of non-perturbative QCD at lowenergies [2,3,4], should be an appropriate framework to tackle this problem in a systematic fashion. However, it was soon noticed that the leading-order chiral corrections are large and tend to worsen the results [5,6]. This problem has often been used to question the validity of SU(3)-χPT in the baryon sector.In the last decade several calculations in HBχPT up to nextto-next-to-leading order (NNLO) have been performed both with [6,7,8] and without [9] the inclusion of the baryon decuplet. The large number of LECs appearing at this order reduces the predictive power of the theory. Besides that, it is also known that there are substantial relativistic corrections [10].The development of covariant χPT has been troubled by the complications in the power counting introduced by the baryon mass as a new large scale [3]. Different ways of solving this problem, such as the IR [11] and, more recently, the EOMS [12] renormalization schemes, have been explored. In SU(3) BχPT only the self-energies have been studied with both schemes [13,14]. The baryon-octet magnetic moments have been calculated using the IR method [15] and, at NLO, the SU(3)-breaking corrections are still large. Moreover, the agreement with the data is even worse than in HBχPT. The size of NLO terms raises the question about the convergence of the chiral series [7,9,16].In this letter we present a covariant calculation of the baryon-octet magnetic moments at O(p 3 ) (NLO) using the EOMS renormalization technique. In contrast to the previous works, we find small loop-corrections leading to a considerable improvement over the SU(3)-symmetric description. We also show the results in HB and covariant IR χPT, and investigate the origin of the differences.In χPT, the power counting (PC) provides a systematic organization of amplitudes as a perturbative expansion in powers of (p/Λ χSB ) nχP T , where p is a small momentum or scale and Λ χSB , the chiral symmetry breaking scale. In the onebar...

Further work performed on this reaction revealed that the integrations over the polar angle in Eqs.(2)-(5) were numerically inaccurate. As a consequence, the integrated cross sections given in Figs. 2 and 3 are reduced by about 20%. The neutrino-energy dependence of the different curves and their relative positions stay approximately the same so we do not show these figures again.The corrected Table I is given below. See the original article for references to the neutrino fluxes and the experimental data.Notice that the results with the Aachen-Padova flux are underestimated with both sets I and II, although, as stated in the article, these theoretical results should be taken with care because the model is less reliable at such large energies.

We present a calculation of the leading SU(3)-breaking O(p 3 )-corrections to the electromagnetic moments and charge radius (CR) of the lowest-lying decuplet resonances in covariant chiral perturbation theory. In particular, the magnetic dipole moment (MDM) of the members of the decuplet is predicted fixing the only low-energy constant (LEC) present up to this order with the well measured MDM of the Ω − . We predict µ ++ ∆ = 6.04(13) and µ + ∆ = 2.84(2) which agree well with the current experimental information. For the electric quadrupole moment (EQM) and the CR we use state-of-the-art lattice QCD results to determine the corresponding LECs, whereas for the magnetic octupole moment (MOM) there is no unknown LEC up to the order considered here and we obtain a pure prediction. We compare our results with those reported in large Nc, lattice QCD, heavy-baryon chiral perturbation theory and other models.

We report a theoretical study of the pp → pK + Λ(1405) reaction, which was recently investigated at COSY-Jülich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. The reaction is driven by single kaon exchange, single pion exchange, and single rho exchange terms which have very different shapes due to the two pole structure of the Λ(1405) and the presence of background terms. The shape for the sum of the three contributions, as well as the total cross section, are consistent with present data within experimental and theoretical uncertainties, using reasonable form factors for the meson-baryon vertices.

We extend an earlier study of the baryon magnetic moments in chiral perturbation theory by the explicit inclusion of the spin-3/2 decuplet resonances. We find that the corrections induced by these heavier degrees of freedom are relatively small in a covariant framework where unphysical spin-1/2 modes are removed. Consequently, implementing the leading SU(3)-breaking corrections given by both the baryon and decuplet contributions, we obtain a description of the baryon-octet magnetic moments that is better than the Coleman-Glashow relations. Finally, we discuss the uncertainties and compare between heavy baryon and covariant approaches.