Axial Mesons Research Articles

Hard pions and axial meson exchange currents in nuclear physics

Starting from the hard meson method we develop a consistent approach to the problem of the axial meson exchange currents (MEC). This method incorporates the current algebra and PCAC together with the vector dominance and allows one to study the pion as well as heavy-meson exchanges on an equal footing. Using a minimal, chiral and approximately gauge-invariant phenomenological Lagrangian (PL) model for the A 1ρπ system we construct the two-nucleon axial MEC operator in the tree approximation. This operator automatically possesses the correct chiral SU(2) × SU(2) transformation properties and has the smoothest momentum dependence which is allowed within the combined current algebra and vector dominance approaches. In the given model, we consider the non-Born part of the amplitude N + J A → n + π and demonstrate that in the soft pion limit, it exactly coincides with the PCAC prediction.

Collective excitations of gluons

Three gauge invariant antisymmetric tensor fields are introduced in the nonabelian gauge theories. They are certain non-linear combinations of the conjugate field tensor and they obey O(3) algebra. An effective chiral lagrangian for these fields is derived. It describes 3 vector and 3 axial mesons with vacuum quantum numbers. The masses are generated by spontaneous restoration of Lorentz invariance.

Radiative decays of 2++ and 1++ mesons

Radiative decays of tensor and axial mesons are considered in the framework of a previously proposed scheme, where the basic currents ofSU4 are dominated by vector mesons and exhibit a quark structure asymptotically. Agreement is found with previousSU3 estimates. The decay rates for ψ′ → γχ1,2 also agree with experiments and nonrelativistic estimates. Conversely, the χ1,2 → γJ/ψ widths have been found smaller by about a factor of two than those obtained in the n.r. bound-state picture. Our results are also compared with those previously obtained for the χ0-meson.

The decoupling of axial mesons from currents

The decoupling of axial mesons from currents

A Regge model for production of axial vector mesons in pion-nucleon collisions

The reactions pseudoscalar+nucleon→axial+nucleon and pseudoscalar+nucleon→axial+3/2+-resonance, are discussed. The general Regge-pole formalism is first developed in detail. It is subsequently specialized in the following steps: i) production near the forward direction, ii) validity ofSU3 (with breakings for meson mixings); iii) validity of exchange degeneracy. Two nonets of produced axial mesons are considered: theA-nonet (JPC=1++) and theB-nonet (JPC=1+−) and the effects of the possibleA-B mixings are examined. The most specific model, assumingSU3 and exchange degeneracy, gives rise to a large number of restrictions (mostly inequalities) among cross-sections which should be testable. The value ofD/F for the couplings of theR-trajectories to nucleons is a relevant unknown parameter; we calculate its value in the kinetic supermultiplet model for a possible indication. The problem of KA-KB interference is discussed and the implied shape of the K* mass spectra is examined.

The mass relation mA = √2 mϱ from current algebra and the Kroll-Ruderman theorem

Assuming that the low-energy s-wave photopion production amplitude is dominated by the axial meson, we derive the Weinberg's relation m A = √2 m ϱ in the framework of current algebra.

Axial mesons, current algebra and superconvergent relations

Axial mesons, current algebra and superconvergent relations

Partial symmetry and meson couplings

Schwinger's hypothesis of partial symmetry is used for calculating the couplings of tensor, axial and scalar mesons to vectors and pseudoscalars. The decay widths of principal modes, evaluated on the basis of a universal coupling equal to the isospin coupling, are in good agreement with experiment.

Axial meson exchange and the relation of hydrogen hyperfine splitting to electron scattering

Axial meson exchange and the relation of hydrogen hyperfine splitting to electron scattering