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, f0 and a0 resonances. The ππ → ππ , ππ → K...

The role of pion rescattering in ππ decay of radially excited heavy quarkonia modeled in terms of a Qππ coupling, is investigated within the framework of the covariant Blankenbecler-Sugar equation. The effects of pion rescattering (or pion exchange) are shown to be large, unless the coupling of the two-pion system to the heavy quarks is mediated by a fairly light scalar σ meson, which couples t...

Extended analysis of the " penguin " part of K → ππ amplitude Abstract We make an attempt to clarify the role of the annihilation or " penguin " mode in the description of the K → ππ decay within the Standard Model. The attention is concentrated on new operators in the effective ∆S = 1 Hamiltonian and the violation of factorization for mesonic matrix elements of the local four-quark operators. ...

The decays of B mesons to the charmless final states ππ and Kπ are a rich source of information on the fundamental parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, but the extraction of this information from data requires the separation of weak interaction effects from strong-interaction quantities such as magnitudes of operator matrix elements and strong phases. A number of model-inde...

The decays of B mesons to the charmless final states ππ and Kπ are a rich source of information on the fundamental parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, but the extraction of this information from data requires the separation of weak interaction effects from strong-interaction quantities such as magnitudes of operator matrix elements and strong phases. A number of model-inde...

The influence of the hadronic ππ interaction on the wave functions of pionium (the Coulomb bound π+π− system) at distances ≤ 10 fm is calculated for s-states with principal quantum numbers n ≤ 4. Hadronic ππ potentials are used that reproduce the scattering phase shifts of two-loop chiral perturbation theory. The pionium wave functions ψn(r) are obtained by integrating the coupled Schrödinger e...

Chiral nonperturbative approach to the isoscalar s-wave ππ interaction in a nuclear medium Abstract The s-wave isoscalar amplitude for ππ scattering in a nuclear medium is evaluated using a nonperturbative unitary coupled channels method and the standard chiral Lagrangians. The method has proved successful to describe the ππ properties in the scalar isoscalar channel up to 1.2 GeV giving rise t...

We investigate the structure of the scalar mesons f0(975) and a0(980) within realistic meson-exchange models of the ππ and πη interactions. Starting from a modified version of the Jülich model for ππ scattering we perform an analysis of the pole structure of the resulting scattering amplitude and find, in contrast to existing models, a somewhat large mass for the f0(975) (mf0 = 1015 MeV, Γf0 = ...

Final state interactions in the S–wave ππ system (I=0,2) are reexamined on the basis of the Omnès-Muskhelishvili equation and the coupled channel formalism. The contributions to the pion scalar form factor from ρ and f 2 (1270) exchange in the t–channel and from the f 0 (980) s–channel resonance are separately evaluated and the role of the nontrivial polynomial in the Omnès function in a couple...

K → ππ decays are investigated in the framework of the SU (2) L × U (1) gauge theory of J = 0 mesons proposed in [1], to which is added an interaction between mesons respecting the two symmetries generally attributed to strong interactions, flavour symmetry and parity conservation. It is shown that the damping of the K + → π + π 0 amplitude with respect to the ones of K s → ππ results from a ca...