arXiv subjects

C. Garcia-Recio

Publications and source records attributed to C. Garcia-Recio.

45 records · Page 3Linked to original sources

arXiv2002

Meson-Baryon Interactions in Unitarized Chiral Perturbation Theory

Meson-Baryon Interactions can be successfully described using both Chiral Symmetry and Unitarity. The $s-$wave meson-baryon scattering amplitude is analyzed in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry in the potential. Two body coupled channel unitarity is exactly preserved. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. Off-shell behavior is parameterized in terms of low energy constants. The relation to the heavy baryon limit is discussed. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths baryonic resonances of the N(1535), N(1670), $Λ(1405)$ and $Λ(1670)$ resonances which compare well with accepted numbers.

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arXiv2002

S=--1 Meson-Baryon Scattering in Coupled Channel Unitarized Chiral Perturbation Theory

The $s-$wave meson-baryon scattering amplitude is analyzed for the strangeness $S=-1$ and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four two-body channels have been considered: $\bar K N$, $πΣ$, $ηΛ$, $ K Ξ$. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. Off-shell behaviour is parameterized in terms of low energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths of the $Λ(1405)$ and $Λ(1670)$ resonances which compare well with accepted numbers.

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arXiv2002

Chiral restoration from pionic atoms?

We evaluate widths and shifts of pionic atoms using a theoretical microscopical potential in which the pion decay constant $f_π$ is changed by an in--medium density dependent one ($f_π(ρ)$), predicted by different partial Chiral restoration calculations. We show that the results obtained for shifts and widths are worse than if this modification were not implemented. On the other hand, we argue that in microscopic many body approaches for the pion selfenergy, based on effective Lagrangians, the mechanisms responsible for the change of $f_π$ in the medium should be automatically incorporated. Therefore, the replacement of $f_π$ by $f_π(ρ)$ in the many body derivation of the microscopic potential would be inappropriate.

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arXiv2001

Non-localities and Fermi motion corrections in $K^-$ atoms

We evaluate the p-wave $K^-N$ amplitudes from the chiral Lagrangians and from there construct the p-wave part of the $K^-$ nucleus optical potential plus a small s-wave part induced from the elementary p-wave amplitude and the nuclear Fermi motion. Simultaneously, the momentum and energy dependence of the s-wave optical potential, previously developed, are taken into account and shown to generate a small p-wave correction to the optical potential. All the corrections considered are small compared to the leading s-wave potential, and lead to changes in the shifts and widths which are smaller than the experimental errors. A thorough study of the threshold region and low densities is conducted, revealing mathematical problems for which a physical solution is given.

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arXiv2001

Optical Potentials in Kaonic Atoms

A microscopic optical potential based on a chiral model is used as a starting point for studying kaonic atoms levels. We add to this potential a phenomenological part fitted to the experimentally known shifts and widths of kaonic levels. This fitted potential is used to predict deeply bound atomic levels, as well as nuclear levels. Comparison with the predictions of other optical models found in the literature is done. Also the effects on the kaonic atoms levels of certain known non-local contributions to the optical potential are also analyzed.

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arXiv2000

Deeply bound levels in kaonic atoms

Using a microscopic antikaon-nucleus optical potential recently developed by Ramos and Oset (nucl-th/9906016, in print in Nuclear Physics A) from a chiral model, we calculate strong interaction shifts and widths for $K^-$ atoms. This purely theoretical potential gives an acceptable description of the measured data ($χ^2/{\rm num.data}= 3.8$), though it turns out to be less attractive than what can be inferred from the existing kaon atomic data. We also use a modified potential, obtained by adding to the latter theoretical one a s-wave term which is fitted to known experimental kaonic data ($χ^2/{\rm degree of freedom}= 1.6$), to predict deeply bound $K^-$ atomic levels, not detected yet. This improved potential predicts, in general, states even narrower than those recently reported by Friedman and Gal. (Phys.Let.B459, 1999, 43). This reinforces the idea that these deeply atomic states can be detected and resolved by using suitable nuclear reactions. Besides, we also study $K^-$ and $\bar K^0$ nuclear bound states and compute binding energies and widths, for both species of antikaons, in $^{12}$C, $^{40}$Ca and $^{208}$Pb. Despite of restricting our study only to potentials obtained from best fits to the known kaonic atom data, the dynamics of these nuclear bound states depend dramatically on the particular optical potential used.

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arXiv1998

Double $Λ$ Hypernuclei and the Nuclear Medium Effective $ΛΛ$ Interaction

We fit the $^1 S_0 ΛΛ$ interaction in the nuclear medium to the masses of the experimentally known double-$Λ$ hypernuclei: $^{\phantom{6}6}_{ΛΛ}$He, $^{10}_{ΛΛ}$Be and $^{13}_{ΛΛ}$B. We derive this effective interaction from OBE Jülich $ΛΛ$-type potentials and using both Hartree-Fock and variational approaches. We find that the inclusion of $ΛΛ$ correlations in the variational scheme leads to significant differences and a better understanding of the dynamical features of the system. We investigate the sensitivity of the binding energies and the mesonic decay widths of the above double-$Λ$ hypernuclei to the $ωΛΛ$ coupling and the form factor at the $σΛΛ$ vertex. We also use this effective interaction to predict binding energies and pionic decay widths of heavier double-$Λ$ hypernuclei, not discovered yet. Finally, we discard the existence of $^1 S_0$ $ΛΛ$ bound states provided the $ΛΛ-ΞN$ coupling can be neglected.

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arXiv1997

Quasielastic K-nucleus scattering

Quasielastic K^+ - nucleus scattering data at q=290, 390 and 480 MeV/c are analyzed in a finite nucleus continuum random phase approximation framework, using a density-dependent particle-hole interaction. The reaction mechanism is consistently treated according to Glauber theory, keeping up to two-step inelastic processes. A good description of the data is achieved, also providing a useful constraint on the strength of the effective particle-hole interaction in the scalar-isoscalar channel at intermediate momentum transfers. We find no evidence for the increase in the effective number of nucleons participating in the reaction which has been reported in the literature.

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arXiv1994

Pion Cloud Contribution to K+ Nucleus Scattering

A careful reanalysis is done of the contribution to $K^{+}$ nucleus scattering from the interaction of the kaon with the virtual pion cloud. The usual approximations made in the evaluation of the related kaon selfenergy are shown to fail badly. We also find new interaction mechanisms which provide appreciable corrections to the kaon selfenergy. Some of these contribute to the imaginary part below pion creation threshold. The inclusion of these new mechanisms in the inelastic part of the optical potential produces a significant improvement in the differential and total $K^{+}$ nuclear cross sections. Uncertainties remain in the dispersive part of the optical potential.

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