M. Nagy

Low-energy hadronic interactions beyond the current algebra approach

Abstract Within chiral perturbation theory at the quark level (CHPT)q with linear realization of chiral U(3) × U(3) symmetry the new low-energy AP3-interaction, produced by convergent box-constituent-quark-loop diagrams, is obtained, and its contributions to processes of low-energy interactions of low-lying mesons are investigated. The new interaction goes beyond the framework of the low-energy current algebra approach and effective chiral Lagrangians with linear realization of chiral symmetry, constructed at the hadronic level.

Linear σ model in one-quark-loop order and the low-energy theorem for the a1 → π(ππ)s-wave decay

Abstract Within the framework of the linear σ model with SU (2) × SU(2) realization of chiral symmetry we prove a low-energy theorem for the a1 → π(ππ)s-wave decay amplitude. this theorem demonstrates the vanishing of the overall amplitude at the zero momentum of any interacting pion in a manner compatible with experimental data.

On the problem of D-meson leptonic and semileptonic decays

Abstract The infinite mass effective theory, when a heavy quark mass goes to infinity, and chiral perturbation theory at the quark level, based on the extended Nambu-Jona-Lasinio model, are applied for the description of form factors of semileptonic decay D→ K e + ν e and leptonic constant FD of D-mesons. The relation is derived connecting the form factor f+(0) with the ratio F D F π , which gives the estimate F D F π =1.21±0.17 . The slope parameter of the f+ form factor is calculated in agreement with experimental data.

Scalar mesons in a chiral quark model with glueball

Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3) × U(3) chiral quark model of the Nambu-Jona-Lasinio (NJL) type with’ t Hooft interaction. The latter interaction produces singlet-octet mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and the glueball and their main modes of strong decay are described.

The existence of low-lying mesons as a consequence of confinement

Abstract We use the Bethe-Salpeter equation for the investigation of the mass spectra of four nonets of low-lying mesons (pseudoscalar, scalar, vector and axial-vector) within QCD with a linearly rising potential. In leading order in the large- N expansion and in the chiral limit the mass spectra are found in agreement with those predicted by the extended Nambu-Jona-Lasinio model. We show that due to the confinement potential the nonets of vector and axial-vector mesons are stable under decays into quark-antiquark pairs.

The low-energy theorem for a1→π(ππ)S-wave decay

Abstract We discuss the paper by Bernard, Osipov and Meiβner (BOM) [preprint BUTP-92/xx, CRN 92-25], on the critical analysis of the low-energy theorem for the a 1 → π ( ππ ) S-wave decay, proposed by Ivanov, Nagy and Scadron (the INS-theorem) [Phys. Lett. B 273 (1991) 137]. The validity of the INS-theorem is confirmed.

Is Cronin's representation correct for the penguin operator?

Abstract It is shown that Cronins operator, used for a phenomenological description of non-leptonic K -meson decays within the effective chiral lagrangian approach with a non-linear realization of chiral SU(3)×SU(3) symmetry (the so-called chiral perturbation theory at the hadronic level), cannot be applied to the determination of the penguin operator (the O 5 -operator) at the hadronic level. The affirmation is based on the proof of the violation of the low-energy theorem lim p +→0 π + (p + ) π − (p _ ) |O 5 | K 0 (p)>=(i/F π ) π 0 (p)| O 5 | K 0 (p)> which is valid within the framework of Cronins representation. The violation of this low-energy theorem is obtained at the quark level and connected with the account of the low-energy interaction of pions caused by the overlap of the wave function of pions in the state | π + π − > at the low-energy limit p + →0. The chiral transformation properties of the normal-ordered penguin operator are studied.

The pion-nucleon Σ-term in the quark model of superconductivity type

Abstract The pion-nucleon Σ-term is evaluated in the framework of the quark model of superconductivity type. The theoretical value is in good agreement with the experimental one. The result obtained stems from the assumption of the absence of s-quarks in the valence structure of the proton.

Decays of excited pseudoscalar and vector mesons in the chiralU(3) ×U(3) model

SummaryA chiralU(3) ×U(3) Lagrangian containing, besides the usual meson fields, their first radial excitations is considered. The Lagrangian is derived by bosonization of the Nambu-Jona-Lasinio (NJL) quark model with separable nonlocal interactions. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the pion, ρ, ω, kaon, K* and ϕ are described with the help of form factors. The values for the decay widths for the processes π′ → ρπ, ρ′ → 2π, ρ′ → ωπ, ω′ → ρπ, K*′ → ρK, K*′ → K*π, K*′ → Kπ, K′ → K*K, K′ → K, K′ → Kρ, K′ → K*π and K′ → K2π are obtained in satisfactory agreement with the experimental data.

Chiral symmetry breaking in QCD with linearly rising confinement potential

SummaryChiral symmetry breaking is explored within QCD with linearly rising confinement potential at the Nambu-Jona-Lasinio (NJL) prescription. The dynamical quark mass is obtained from the gap equation in terms of the string tension σ, σ,i.e.m=2蜰σ/π=0.33 GeV at σ=0.27 GeV2. The phenomenological constants of the NJL local four-quark interactionsG1 andG2 are found equal and expressed in terms of the string tension and the confinement radius. It is shown that the spectra of low-lying quark-antiquark collective excitations coincide with those predicted by the NJL model.