Noninvariance Groups and Low-Energy Meson-Baryon Scattering (original) (raw)

An indication for «three component» duality in finite-energy sum rules for pion-nucleon scattering

Il Nuovo Cimento A, 1980

fit to finite-energy sum rules for the amplitude B(-) in pion-nucleon scattering at various momentum transfers in terms of a dominant p trajectory provides much more satisfactory results if the Born-term contribution is subtracted from the sum rules. This result may give an indication in favour of what could be called <~ threecomponent duality ~>, in which, besides the well-known correspondence between pomeron and diffraction, and between moving Regge poles and resonances, there is a further correspondence between nonstandard singularities (e.g. fixed poles) and Born terms.

Meson-meson and meson-nucleon scattering and the structure of hadrons

Nuclear Physics A, 1998

Effective meson Lagrangians are the appropriate theoretical tool for the non-perturbative regime of QCD which in the present work is applied to meson-meson and meson nucleon systems. For the meson-meson part we concentrate our interest on the 1.0 GeV region where we investigate the structure of the scalar mesons f0(980) and a0(980) in 7r~r and ~rr/ scattering, respectively. It is shown that our model is compatible with all available data__ sets and provides a consistent understanding of both mesons f0(980) and a0(980) as KK threshold effects. In the second part, we investigate pion-nucleon scattering. Here we focus our interest on the first excited states of the nucleon. We discuss the interplay between genuine poles and resonance behavior due to the meson baryon dynamics. In the case of the A-isobar we find that the non-pole background plays a crucial role for the quantitative understanding of the A width. The Pll partial wave of 7rN scattering is described without inclusion of a genuine N* (Roper) resonance. In the pion production region the effect of coupling to the reaction channels 7rA and crN is investigated. 0375-9474/98/$19

Unitarity sum rules and soft-pion amplitudes

Il Nuovo Cimento A, 1972

We examine uuitarity bounds on scattering amplitudes by using ((unitarity sum rules ,~ at high energy. Threshold conditions emerge when certain mass parameters approach zero. For r:= scattering a bound similar to (but somewhat weaker than) the Adler condition is shown to be needed in ordel to avoid a dangerous mass (infra-red) singularity. A diffcrcnt argument, which uses crucially the pseudoscalar nature of the pion and a few very plausible dynamical assulnptions, yields a stronger bound as well as the possibility of extension to general pion amplitudes. We finally discuss our results as well as the possibility of understanding spontaneously broken symmetries from general S-matrix principles. ].-Introduction and snmmary of results. It has been pointed out recently (1) that a new approach to the stronginteraction bootstrap program (2.3) is obtained when we replace the usual (*) This work was supported in part through funds provided by tile Atomic Energy Commission under Contract AT(l 1-I)3069.

Meson–baryon couplings and the F/D ratio from QCD sum rules

Nuclear Physics A, 2000

Motivated by the recent work on the calculation of the πN N coupling constant using QCD sum rule beyond the chiral limit, we construct the corresponding sum rules for the couplings, ηN N , πΞΞ, ηΞΞ, πΣΣ and ηΣΣ. In constructing the η-baryon sum rules, we use the second moment of the η wave function, which we obtain from the pion wave function after SU(3) rotation. In the SU(3) symmetric limit, we can identify the term responsible for the F/D ratio in the OPE, which after the sum rule analysis gives F/D ∼ 0.2, a factor of 3 smaller than from other studies. We also present a qualitative analysis including the SU(3) breaking terms.

The pion-pion scattering amplitude

2004

We obtain reliable ππ scattering amplitudes consistent with experimental data, both at low and high energies, and fulfilling appropriate analyticity properties. We do this by first fitting experimental low energy (s^1/2≤1.42 GeV) phase shifts and inelasticities with expressions that incorporate analyticity and unitarity. In particular, for the S wave with isospin 0, we discuss in detail several sets of experimental data. This provides low energy partial wave amplitudes that summarize the known experimental information. Then, we impose Regge behaviour as follows from factorization and experimental data for the imaginary parts of the scattering amplitudes at higher energy, and check fulfillment of dispersion relations up to 0.925 GeV. This allows us to improve our fits. The ensuing ππ scattering amplitudes are then shown to verify dispersion relations up to 1.42 GeV, as well as s - t - u crossing sum rules and other consistency conditions. The improved parametrizations therefore provi...

Relativistic chiral SU(3) symmetry, large-Nc sum rules and meson–baryon scattering

Nuclear Physics A, 2002

The relativistic chiral SU (3) Lagrangian is used to describe kaon-nucleon scattering imposing constraints from the pion-nucleon sector and the axial-vector coupling constants of the baryon octet states. We solve the covariant coupled-channel Bethe-Salpeter equation with the interaction kernel truncated at chiral order Q 3 where we include only those terms which are leading in the large N c limit of QCD. The baryon decuplet states are an important explicit ingredient in our scheme, because together with the baryon octet states they form the large N c baryon ground states of QCD. Part of our technical developments is a minimal chiral subtraction scheme within dimensional regularization, which leads to a manifest realization of the covariant chiral counting rules. All SU(3) symmetry-breaking effects are well controlled by the combined chiral and large N c expansion, but still found to play a crucial role in understanding the empirical data. We achieve an excellent description of the data set typically up to laboratory momenta of p lab ≃ 500 MeV.

Aspects of meson-baryon scattering in three- and two-flavor chiral perturbation theory

Physical Review D, 2009

We analyze meson-baryon scattering lengths in the framework of covariant baryon chiral perturbation theory at leading one-loop order. We compute the complete set of matching relations between the dimension-two low-energy constants in the two-and three-flavor formulations of the theory. We derive new two-flavor low-energy theorems for pion-hyperon scattering that can be tested in lattice simulations.

It=JtRule: A New Large-NcSelection Rule for Meson-Baryon Scattering

Physical Review Letters, 1988

Quasielastic meson-baryon scattering is reformulated in t-channel language (meson exchange) instead of s-channel language (baryon-resonance formation), by use of skyrmion methods. A new selection rule emerges, valid to leading order in large N, : The isospin of the exchanged state must equal its total angular momentum (spin+orbital). Difl'erences between the two-flavor and the three-flavor approach are discussed.