arXiv subjects

D. Jido

Publications and source records attributed to D. Jido.

At least 73 records · Page 4Linked to original sources

arXiv2004

Chiral dynamics of the two Lambda(1405) states

The Lambda(1405) resonance is studied by a chiral unitary approach, in which the resonance is dynamically generated in coupled-channel meson-baryon scattering. Investigating the analytic structure of the scattering amplitudes obtained by the chiral unitary approach, we find two poles around the energies of the Lambda(1405) coupling differently to the meson-baryon states. We reach the conclusion that the Lambda(1405) resonance seen in experiments is not just one single resonance, but a superposition of these two states.

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arXiv2003

Chiral doublet model for the positive and negative parity nucleons

We discuss the properties of the nucleon (N) and its excited state with odd parity (N*) under the aspect of chiral symmetry, identifying them with suitable representations of the chiral group. It is shown that there are two distinctive schemes to assign the chiral multiplet to N and N*. We construct linear sigma models for N and N* with the two assignments to show their physical implications. We also discuss the in-medium properties of N(1535), comparing the present model with the other chiral model based on the different picture of N*.

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arXiv2003

Regulariztion dependence of S=0 and S=-1 meson-baryon system in the chiral unitary model

We investigate the dependence of s-wave meson-baryon scattering amplitudes on different regularizations within the framework of the chiral unitary model. We employ two different regularization schemes, i.e. dimensional and form-factor regulariaztions to tame the divergences in the model. We also study the analytic structures of T-matrices, using those regularization schemes. We find that while the form-factor regularizaion produces almost the same results as the dimensional regularization did, the on-shell approximation is to some extent limited in the case of the form-factor regularization. Having chosen parameters properly, we show that the regularization dependences can be minimized.

hep-ph↗

arXiv2003

eta-Nucleus interactions and in-medium properties of N*(1535) in chiral models

The properties of eta-nucleus interaction and their experimental consequences are investigated with eta-nucleus optical potentials obtained by postulating the N*(1535) dominance for eta-N system. The N*(1535) properties in nuclear medium are evaluated by two kinds of chiral effective models based on distinct pictures of N*(1535). We find that these two models provide qualitatively different optical potentials of the eta meson, reflecting the in-medium properties of N*(1535) in these models. In order to compare these models in physical observables, we calculate spectra of (d,3He) reactions for the eta mesic nucleus formation with various kinds of target nuclei. We show that the (d,3He) spectra obtained in these models are significantly different and are expected to be distinguishable in experiments.

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arXiv2003

Chiral symmetry aspects of positive and negative parity baryons

Chiral symmetry aspects for baryon properties are studied. After a brief discussion on general framework, we introduce two distinctive chiral group representations for baryons: the naive and mirror assignments. Using linear sigma models, nucleon properties are studied in both representations. Finally, we propose an experiment to distinguish the two assignments in the reactions of pion and eta productions.

hep-ph↗

arXiv2003

Magnetic moments of the N(1535) resonance in the chiral unitary model

We calculate the magnetic moments of the N(1535) resonance using the chiral unitary model, where the resonance is dynamically generated in the scatterings of the lowest-lying mesons and baryons. We obtain the magnetic moments of the resonance as +1.1 and -0.25 for p(1535) and n(1535), respectively, in units of the nuclear magneton. We discuss the origin of these numbers within the chiral unitary model, then we compare the present results with those of the quark model and the chiral doublet model. The possibility to observe the magnetic moments in experiments is also investigated.

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arXiv2003

Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings

We examine flavor SU(3) breaking effects on meson-baryon scattering amplitudes in the chiral unitary model. It turns out that the SU(3) breaking, which appears in the leading quark mass term in the chiral expansion, can not explain the channel dependence of the subtraction parameters of the model, which are crucial to reproduce the observed scattering amplitudes and resonance properties.

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arXiv2003

Chiral Dynamics of the Two Λ(1405) States

Using a chiral unitary approach for the meson--baryon interactions, we show that two octets of J^π=1/2^- baryon states, which are degenerate in the limit of exact SU(3) symmetry, and a singlet are generated dynamically. The SU(3) breaking produces the splitting of the two octets, resulting in the case of strangeness S=-1 in two poles of the scattering matrix close to the nominal Λ(1405) resonance. These poles are combinations of the singlet state and the octets. We show how actual experiments see just one effective resonance shape, but with properties which change from one reaction to another.

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arXiv2002

The $ρNN$ coupling with direct coupling and loops

Starting from a gauge formalism of $ρ$ mesons, pions and baryons we evaluate the $ρ$ coupling to the nucleon, including the direct coupling provided by the Lagrangians, plus contributions from loops with the virtual pion cloud. We find a contribution to the magnetic $ρ$ coupling to the nucleon from pionic loops of the same size as the direct coupling, which is, however, still small compared to the empirical values. This finding goes in line with chiral formulations of the strong interaction of mesons at low energies where, unlike the scalar mesons which are mostly built of a pion (kaon) cloud, the $ρ$ meson stands as a genuine QCD state with intrinsic properties not tied to those of the pion cloud.

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arXiv2002

Medium effects to the N(1535) resonance and eta mesic nuclei

The structure of eta-nucleus bound systems (eta mesic nuclei) is investigated as one of the tools to study in-medium properties of the N(1535) (N*) resonance. We show that, as a general consequence, the eta-nucleus potential has a repulsive core at the nuclear center with an attractive part at the nuclear surface, if sufficient reduction of the mass difference of N and N* stems from the in-medium effects to N*. The (d,3He) spectra are evaluated for the formation of these bound states to investigate the experimental feasibility.

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arXiv2002

Chiral dynamics in systems with strangeness

In this talk a brief review of several problems involving systems with strangeness is made. In the first place one shows how the $Λ(1405)$, $Λ(1670)$ and $Σ(1620)$ states, for $S = -1$, and the $Ξ(1620)$ for $S= -2$ are generated dynamically in the context of unitarized chiral perturbation theory. The results for the $\bar{K}N$ interaction are then used to evaluate the $K^- d$ scattering length. Results obtained for the kaon selfenergy in a nuclear medium within this approach, with application to $K^-$ atoms, are also mentioned. Finally a few words are said about recent developments in the weak decay of $Λ$ hypernuclei and the puzzle of the $Γ_n/Γ_p$ ratio.

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arXiv2002

Medium effects to N(1535) resonance and eta mesic nuclei

The structure of eta-nucleus bound systems (eta mesic nuclei) is investigated as one of the tools to study in-medium properties of the N(1535) (N^*) resonance by using the chiral doublet model to incorporate the medium effects of the N^* resonance in a chiral symmetric way. We find that the shape and the depth of the eta-nucleus optical potential are strongly affected by the in-medium properties of the N^* and the nucleon. Especially, as a general feature of the potential, the existence of a repulsive core of the eta-nucleus potential at the nuclear center with an attractive part at the nuclear surface is concluded. We calculate the level structure of bound states in this 'central-repulsive and surface-attractive' optical potential and find that the level structure is sensitive to the in-medium properties of the N^*. The (d,3He) spectra are also evaluated for the formation of these bound states to investigate the experimental feasibility. We also make comments on the possible existence of halo-like eta states in beta-unstable halo nuclei.

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arXiv2002

Chiral dynamics of p-wave in K^- p and coupled states

We perform an evaluation of the p-wave amplitudes of meson-baryon scattering in the strangeness S=-1 sector starting from the lowest order chiral Lagrangians and introducing explicitly the Sigma^* field with couplings to the meson-baryon states obtained using SU(6) symmetry. The N/D method of unitarization is used, equivalent, in practice, to the use of the Bethe-Salpeter equation with a cut-off. The procedure leaves no freedom for the p-waves once the s-waves are fixed and thus one obtains genuine predictions for the p-wave scattering amplitudes, which are in good agreement with experimental results for differential cross sections, as well as for the width and partial decay widths of the Sigma^*(1385).

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arXiv2002

Magnetic moments of the Lambda(1405) and Lambda(1670) resonances

By using techniques of unitarized chiral perturbation theory, where the $Λ(1405)$ and $Λ(1670)$ resonances are dynamically generated, we evaluate the magnetic moments of these resonances and their transition magnetic moment. The results obtained here differ appreciably from those obtained with existing quark models. The width for the $Λ(1670) \to Λ(1405) γ$ transition is also evaluated leading to a branching ratio of the order of $2 \times 10^{-6}$.

hep-ph↗

arXiv2002

Determination of the axial coupling constant $g_{A}$ in the linear representations of chiral symmetry

If a baryon field belongs to a certain linear representation of chiral symmetry of $SU(2) \otimes SU(2)$, the axial coupling constant $g_{A}$ can be determined algebraically from the commutation relations derived from the superconvergence property of pion-nucleon scattering amplitudes. This establishes an algebraic explanation for the values of $g_{A}$ of such as the non-relativistic quark model, large-$N_{c}$ limit and the mirror assignment for two chiral partner nucleons. For the mirror assignment, the axial charges of the positive and negative parity nucleons have opposite signs. Experiments of eta and pion productions are proposed in which the sign difference of the axial charges can be observed.

hep-ph↗

arXiv2001

Meson exchange in the weak decay of Lambda hypernuclei and the Gamma_n/Gamma_p ratio

We take an approach to the Lambda non-mesonic weak decay in nuclei based on the exchange of mesons. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange (sigma-like exchange), or uncorrelated (box diagrams). Extra effects of omega exchange in the scalar-isoscalar channel are also considered. Constraints of chiral dynamics are used to generate these exchanges. A drastic reduction of the OPE results for the Gamma_n/Gamma_p ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in good agreement with experiment.

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arXiv2000

Chiral symmetry and meson exchange approach to hypernuclear decay

We take an approach to the $Λ$ nonmesonic weak decay in nuclei based on the exchange of mesons under the guidelines of chiral Lagrangians. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange ($σ$-like exchange), or uncorrelated (box diagrams). A drastic reduction of the OPE results for the $Γ_n/Γ_p$ ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in fair agreement with experiment.

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arXiv2000

In-medium pi-pi Correlation Induced by Partial Restoration of Chiral Symmetry

We show that both the linear and the non-linear chiral models give an enhancement of the pi-pi cross section near the 2pi threshold in the scalar-iso-scalar (I=J=0) channel in nuclear matter. The reduction of the chiral condensate, i.e., the partial chiral restoration in nuclear matter, is responsible for the enhancement in both cases. We extract an effective 4pi-nucleon vertex which is responsible for the enhancement but has not been considered in the non-liear models for in-medium pi-pi interaction. Relation of this vertex and a next-to-leading order terms in the heavy-baryon chiral lagrangian, L_piN^(2), is also discussed.

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