arXiv subjects

J. A. Oller

Publications and source records attributed to J. A. Oller.

121 records · Page 7Linked to original sources

arXiv1998

A coupled channel unitary chiral approach to the meson-meson interaction and pion-pion scattering in a nuclear medium

A new tool which combines chiral perturbation theory and unitarity in coupled channels is applied with success to the study of the meson-meson interaction, extending the theoretical predictions up to sqrt{s} = 1.2 GeV, hence improving considerably the convergence radius of conventional chiral perturbation theory. The method is applied to obtain the meson-meson phase shifts and inelasticities as well as the isoscalar pion-pion scattering amplitude inside a nuclear medium.

hep-ph↗

arXiv1998

Non-perturbative chiral approach to Kp -->gamma Y reactions

A recently developed nonperturbative chiral approach to describe the S=-1 meson-baryon reactions has been extended to investigate the near threshold $K^- p \to γΛ, γΣ^0$ reactions. With the parameters governed by chiral SU(3) symmetry, we show that the predicted branching ratios $Γ_{K^- p \to γΛ}/Γ_{K^- p \to all}$ and $Γ_{K^-p\to γΣ^0}/Γ_{K^- p \to all}$ are close to the experimental values. The coupling with the $η$ channels, which was shown to be important in the $S=-1$ meson-baryon reactions, is also found to be significant here. Our results are consistent with the interpretation of the $Λ(1405)$ as a quasi-bound meson-baryon state as found in other similar chiral approaches.

nucl-th↗

arXiv1998

Meson-Meson and Meson-Baryon Interactions in a chiral Non-perturbative Approach

A qualitative account of the meson-meson and meson-baryon interactions using chiral Lagrangians and the inverse amplitude method in coupled channels is done. The method, imposing exact unitarity, proves to be very useful tool to extend the information contained in the chiral Lagrangians at energies beyond the realm of applicability of chiral perturbation theory.

hep-ph↗

arXiv1998

Meson-Meson interaction in a non-perturbative chiral approach

A non-perturbative method which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe the meson-meson interaction up to about 1.2 GeV. The approach uses the O(p^2) and O(p^4) chiral Lagrangians. The seven free parameters of the O(p^4) Lagrangian are fitted to the data. The results are in good agreement with a vast amount of experimental analyses. The amplitudes develop poles in the complex plane corresponding to the f0, a0, rho, K*, phi, sigma and kappa resonances; the latter two, very broad. The total and partial decay widths of the resonances are also well reproduced. Further extensions and applications of this chiral non-perturbative scheme are also discussed.

hep-ph↗

arXiv1998

Non-perturbative Approach to effective chiral Lagrangians and Meson Interactions

We develop a coupled channel unitary approach describing the behavior at higher energies of systems whose low-energy dynamics is given by effective O(p^2) and O(p^4) chiral Lagrangians. Our free parameters are those of the O(p^4) Lagrangian. When applied to the meson-meson interaction, it yields a remarkable agreement with data up to sqrt{s}=1.2 GeV, dynamically generating the sigma, f_0, a_0,rho and K^* resonances. Further applications are also proposed.

hep-ph↗

arXiv1998

The phi --> gamma K0 bar(K0) Decay

The study of the process phi-->gamma K0 bar(K0) is calculated to be 5.10^(-8) in a scheme which takes into account the different isospin channels involved, I=0,1 with the resonant, f_0(980), a_0(980), and non resonant contributions.

hep-ph↗

arXiv1997

Delta excitation in K^+-nucleus collisions

We present calculations for Δexcitation in the (K^+,K^+) reaction in nuclei. The background from quasielastic K^+ scattering in the Δregion is also evaluated and shown to be quite small in some kinematical regions, so as to allow for a clean identification of the Δexcitation strength. Nuclear effects tied to the Δrenormalization in the nucleus are considered and the reaction is shown to provide new elements to enrich our knowledge of the Δproperties in a nuclear medium.

nucl-th↗

arXiv1997

Theoretical Study of the γγ-->meson-meson Reaction

We present a unified picture which studies simultaneously the gamma gamma-->pi^+ pi^-, pi^0 pi^0, K^+ K^-, K^0 bar{K}^0, pi^0 eta reactions up to about sqrt(s)=1.4 GeV reproducing the experimental cross sections. The present work implements in an accurate way the final state interactions of the meson-meson system, which is shown to be essential in order to reproduce the data, particularly the L=0 channel. This latter channel is treated here following a recent theoretical work in which the meson-meson amplitudes are well reproduced and the f_0, a_0, sigma resonances show up clearly as poles of the t matrix. The present work, as done in earlier ones, also incorporates elements of chiral symmetry and exchange of vector and axial resonances in the crossed channels, as well as a direct coupling to the f_2(1270) and a_2(1320) resonances. We also evaluate the decay width of the f_0(980) and a_0(980) resonances into the gamma-gamma channel.

hep-ph↗

arXiv1997

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the sigma, f_0(980), a_0(980) scalar mesons (HADRON'97)

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the sigma, f_0 and a_0 resonances. The ππ--> ππ, ππ--> K bar(K) phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π^0 eta and K bar(K) mass distributions in the T=1 channel. Furthermore, the total and partial strong decay widths of the f_0 and a_0 resonances are properly reproduced.

hep-ph↗

arXiv1997

Theoretical Study of the γγ-->meson-meson Reaction (HADRON'97)

We present a unified picture which studies simultaneously the gamma gamma--> pi^+ pi^-, pi^0 pi^0,K^+ K^-, K^0 bar{K}^0, pi^0 eta reactions up to about sqrt(s)=1.4 GeV reproducing the experimental cross sections. The present work implements in an accurate way the final state interactions of the meson-meson system, which is shown to be essential in order to reproduce the data, particularly the L=0 channel. This latter channel is treated here following a recent theoretical work in which the meson-meson amplitudes are well reproduced and the f_0, a_0, sigma resonances show up clearly as poles of the t matrix. The present work, as done in earlier ones, also incorporates elements of chiral symmetry and exchange of vector and axial resonances in the crossed channels, as well as a direct coupling to the f_2(1270) and a_2(1320) resonances. We also evaluate the decay width of the f_0(980) and a_0(980) resonances into the gamma-gamma channel.

hep-ph↗

arXiv1997

Chiral symmetry amplitudes in the s-wave isoscalar and isovector channels and the $σ, f_0(980), a_0 (980)$ scalar mesons

We use a nonpertubative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the $σ$, f_0 and a_0 resonances. The $ππ\to ππ, ππ\to K \bar{K}$ phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the $π^0 η$ and $K \bar{K}$ mass distributions in the T = 1 channel. Furthermore, the total and partial decay widths of the f_0 and a_0 resonances are properly reproduced including also the decay into the $γγ$ channel. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below $\sqrt{s} \simeq 1.2 GeV$.

nucl-th↗

arXiv1997

Chiral Symmetry Amplitudes in the S-Wave Isoscalar and Isovector Channels and the σ, f_0(980), a_0(980) Scalar Mesons

We use a nonperturbative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangians. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ,f_0 and a_0 resonances. The ππ-->ππ, ππ-->K\bar{K} phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π^-ηand K^-K^0 mass distributions in the T=1 channel. Furthermore, the total and partial decay widths of the f_0 and a_0 resonances are properly reproduced including also the decay into the γγchannel. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below \sqrt(s)=1.2 GeV.

hep-ph↗

arXiv1997

Meson Exchange Currents in Kaon Scattering on the Lightest Nuclei

The K^+ scattering on the lightest nuclei, d, 3He and 4He is studied in the framework of multiple scattering theory. Effects from MEC tied to the K^+N-->KNpi reaction are evaluated. We found that at momentum transfers Q^2<0.5 (GeV/c)^2 contributions from MEC are much smaller than kaon rescattering corrections. This makes the conventional multiple scattering picture a reliable tool to study these reactions in this kinematical domain and to extract the K^+n scattering amplitude from the K^+d data. At larger transferred momentum MEC can become more relevant.

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