L. S. Geng

Leading SU(3)-breaking corrections to the baryon magnetic moments in chiral perturbation theory.

We calculate the baryon magnetic moments using covariant chiral perturbation theory (chiPT) within the extended-on-mass-shell renormalization scheme. By fitting the two available low-energy constants, 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 chiPT and covariant infrared chiPT. We also analyze the source of this improvement with particular attention to the comparison between the covariant results.

Lowest-lying baryon masses in covariant SU(3)- flavor chiral perturbation theory

We present an analysis of the baryon-octet and -decuplet masses using covariant SU(3)-flavor chiral perturbation theory up to next-to-leading order. Besides the description of the physical masses we address the problem of the lattice QCD extrapolation. Using the PACS-CS Collaboration data we show that a good description of the lattice points can be achieved at next-to-leading order with the covariant loop amplitudes and phenomenologically determined values for the meson-baryon couplings. Moreover, the extrapolation to the physical point up to this order is found to be better than the linear one given at leading-order by the Gell-Mann-Okubo approach. The importance that a reliable combination of lattice QCD and chiral perturbation theory may have for hadron phenomenology is emphasized with the prediction of the pion-baryon and strange-baryon sigma terms.

Electromagnetic structure of the lowest-lying decuplet resonances in covariant chiral perturbation theory

We present a calculation of the leading SU(3)-breaking O(p{sup 3}) corrections to the electromagnetic moments and charge radius of the lowest-lying decuplet resonances in covariant chiral perturbation theory. In particular, the magnetic dipole moment of the members of the decuplet is predicted fixing the only low-energy constant (LEC) present up to this order with the well-measured magnetic dipole moment of the {omega}{sup -}. We predict {mu}{sub {delta}}{sup ++}=6.04(13) and {mu}{sub {delta}}{sup +}=2.84(2), which agree well with the current experimental information. For the electric quadrupole moment and the charge radius, we use state-of-the-art lattice QCD results to determine the corresponding LECs, whereas for the magnetic octupole moment 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 N{sub c}, lattice QCD, heavy-baryon chiral perturbation theory, and other models.

Leading-order decuplet contributions to the baryon magnetic moments in chiral perturbation theory

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.

Clues for the existence of two K 1 ( 1270 ) resonances

The axial-vector meson K{sub 1}(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{sup -}p{yields}K{sup -}{pi}{sup +}{pi}{sup -}p at 63 GeV, which established the existence of both K{sub 1}(1270) and K{sub 1}(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.

Study of the f2(1270) , f2′(1525) , f0(1370) and f0(1710) in the J/ψ radiative decays

In this paper we present an approach to study the radiative decay modes of the J/ψ into a photon and one of the tensor mesons f2(1270) , f′2(1525) , as well as the scalar ones f0(1370) and f0(1710) . Especially, we compare predictions that emerge from a scheme where the states appear dynamically in the solution of vector meson-vector meson scattering amplitudes to those from a (admittedly naive) quark model. We provide evidence that it might be possible to distinguish amongst the two scenarios, once improved data are available.

Nature of the axial-vector mesons from their N-c behavior within the chiral unitary approach

By describing within the chiral unitary approach the s -wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone bosons, we find that the main component of the axial-vector mesons --b1(1235) , h1(1170) , h1(1380) , a1(1260) , f1(1285) and the two states associated to the K1(1270) -- does not follow the QCD dependence on the number of colors for ordinary q

Octet-baryon axial-vector charges and SU(3)-breaking effects in the semileptonic hyperon decays

\bar{{q}}

Study of the J/ψ→ϕ(ω)f2(1270), J/ψ→ϕ(ω)f2′(1525) and J/ψ→K∗0(892)K¯2∗0(1430) decays

mesons.

Nucleon-to-{delta} axial transition form factors in relativistic baryon chiral perturbation theory

The octet-baryon axial-vector charges and the g1/f1 ratios measured in the semileptonic hyperon decays are studied up to O(p^3) using the covariant baryon chiral perturbation theory with explicit decuplet contributions. We clarify the role of different low-energy constants and find a good convergence for the chiral expansion of the axial-vector charges of the baryon octet, g1(0), with O(p^3) corrections typically around 20% of the leading ones. This is a consequence of strong cancellations between different next-to-leading order terms. We show that considering only non-analytic terms is not enough and that analytic terms appearing at the same chiral order play an important role in this description. The same effects still hold for the chiral extrapolation of the axial-vector charges and result in a rather mild quark-mass dependence. As a result, we report a determination of the leading order chiral couplings, D=0.623(61)(17) and F=0.441(47)(2), as obtained from a completely consistent chiral analysis up to O(p^3). Furthermore, we note that the appearance of an unknown low-energy constant precludes the extraction of the proton octet-charge from semileptonic decay data alone, which is relevant for an analysis of the composition of the proton spin.