On convergence of the ChPT HFF expansion for one loop contribution to meson production in NN collisions

We consider the application of heavy fermion formalism based chiral perturbation theory to meson production in nucleon-nucleon collisions. It is shown that for one loop contributions the heavy fermion formalism expansion corrections for the nucleon propagator produce infinite series of correction terms which are of the same momentum power order. This destroys the one-to-one correspondence between the perturbative and small momentum expansion and thus negates the application of any finite order heavy fermion formalism chiral perturbation theory to the $NN\to NN \pi$ reactions.Comment: 13 pages, 3figure

Effective Chiral Theory for Pseudoscalar and Vector Mesons

We consider the vector meson mixing scheme and mass splitting within the framework of an extended $U(3)_L\bigotimes U(3)_R$ chiral effective field theory based on the hidden local symmetry approach where, the pseudoscalar and vector meson nonets play the role of dynamic variables. Unlike other variants of this model, we show that the diagonalization of the vector meson mass matrix and the assumption that its eigenvalues are identical with the physical meson masses, determines the mixing scheme as well as the model free parameters. We show that VMD can be derived from our lagrangian and that for electromagnetic processes at low momenta the VMD model is a good first approximation. The model reproduces nicely the radii of the charged pions and kaons.Comment: 12 pages, 1 figur

A Covariant OBE Model for η\eta Production in NN Collisions

A relativistic covariant one boson exchange model, previously applied to describe elastic nucleon-nucleon scattering, is extended to study $\eta$ production in NN collisions. The transition amplitude for the elementary BN->$\eta$N process with B being the meson exchanged (B=$\pi$, $|sigma$,$\eta$, $\rho$, $\omega$ and $\delta$) are taken to be the sum of four terms corresponding to s and u-channels with a nucleon or a nucleon isobar N*(1535MeV) in the intermediate states. Taking the relative phases of the various exchange amplitudes to be +1, the model reproduces the cross sections for the $NN\to X\eta$ reactions in a consistent manner. In the limit where all $\eta$'s are produced via N^* excitations, interference terms between the overall contributions from the exchange of pseudoscalart and scalar mesons with that of vector mesons cancel out. Consequently, much of the ambiguities in the model predictions due to unknown relative phases of different vector pseudoscalar exchanges are strongly reduced.Comment: 40 pages, 15 figure

S-wave π0\pi^0 Production in pp Collision in a Covariant OBE Model

The total cross section for the pp -> pp pi^0 reaction at energies close to threshold is calculated using a covariant one-boson-exchange model, where a boson B created on one of the incoming protons is converted into a neutral pion on the second. The amplitudes for the conversion processes, B N -> N pi^0, are taken to be the sum of s, u and t-channel pole terms. The main contributions to the primary production amplitude is due to an effective isoscalar sigma meson pole in a t-channel, which is enhanced strongly due to offshellness. With this contribution included the model reproduces, both the scale and energy dependence of the cross section.Comment: REVTeX, graphicx, 22 pages (icluding 10 figures