Related papers: The $\pi \sigma$-Axial Exchange Current
We calculate the amplitudes of the axion photoproduction off the nucleon, i.e., $\gamma N \to a N$, within the framework of chiral effective field theory. Several different types of contributions are simultaneously included in our…
We discuss electro-magnetic and weak production of pions on nucleons and show how results of experiments and their interpretation in terms of chiral quark models with explicit meson degrees of freedom combine to reveal the ground-state…
We point out that the $\Delta\pi$ component of the nucleon wave function is vital to the interpretation of the recent H1 data for leading baryon production. While the $n/p$ ratio is equal to two with the $N\pi$ component alone, the…
We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit…
A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SCX, DCX, absorption and pion production) at pion energies above 0.5 GeV. Special attention has been paid to pion double charge exchange. Pion…
Based upon the Bonn meson-exchange-model for the nucleon-nucleon ($NN$) interaction, we calculate the charge-independence breaking (CIB) of the $NN$ interaction due to pion-mass splitting. Besides the one-pion-exchange (OPE), we take into…
Current-induced switching is considered in a magnetic junction. The junction includes pinned and free ferromagnetic layers which work in the regime of the high spin injection. It is shown that in such a regime the exchange magnetization…
We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant $g_{NN\pi}$ coming from isospin violation in the strong…
We investigate an extended chiral soliton model which includes $\pi, \rho, \omega$ and $\sigma $ mesons as explicit degrees of freedom. The Lagrangian incorporates chiral symmetry and broken scale invariance. A scalar-isoscalar meson…
We construct a model for the weak pion production off the nucleon, which in addition to the weak excitation of the $\Delta(1232)$ resonance and its subsequent decay into $N\pi$, it includes also some background terms required by chiral…
Taking into account the exchange forces between protons of scalar, pseudoscalar, vector and axial vector type the cross sections of neutral and charged scalar mesons $a_0(980)$, $a_+(980)$, $f_0(980)$, $\sigma(600)$ production are…
We present the contributions of the non-linear chiral scalar field S to cross sections of $pp\to d\pi ^{+}, pp\to pn\pi ^{+}$ and $pp\to pp\pi ^0$ reactions at threshold. We compare our results with the meson $\sigma$ contribution from the…
A theoretical analysis of the $(\pi^-,\gamma\gamma)$ reaction in nuclei is made in order to find the viability of this reaction to test modifications of the $\sigma$ meson mass in nuclear matter. The $\pi\pi$ correlation in the…
Using SU(3) chiral perturbation theory we calculate the density-dependent complex-valued spin-orbit coupling strength $U_{\Sigma ls}(k_f)+ i W_{\Sigma ls}(k_f)$ of a $\Sigma$ hyperon in the nuclear medium. The leading long-range $\Sigma N$…
We present recent Monte Carlo data for the axial charge of the nucleon obtained by the QCDSF-UKQCD collaboration for N_f=2 dynamical quarks. We compare them with formulae from chiral perturbation theory in finite and infinite volume and…
The nucleon-nucleon ($NN$) potential is the residual interaction of the strong interaction in the low-energy region and is also the fundamental input to the study of atomic nuclei. Based on the non-perturbative properties of the quantum…
Resonant-exchange scattering plays a key role in many-body dynamics and transport phenomena (such as spin, charge, or excitation diffusion) at low and moderate temperatures. Recent investigations have shown that the locking of phase shifts…
We present an amplitude analysis of high-energy polarized photoproduction of $\pi^-\Delta^{++}$ within a Regge exchange framework. A Regge amplitude model incorporating $\pi$, $\rho$, $b_1$, and $a_2$ trajectory exchanges is fit…
In this work we study the axion/axion-like particle production from the lepton-nucleon scattering in the low-energy region, i.e., the $\ell N\to \ell N a$ processes, $\ell$ being the electron or muon and $N$ the proton or neutron. We…
We give a brief review on the important role of the pion-exchange interaction characterized by the strong tensor force. In order to illustrate the role of the pion, we have proposed a new mean field theory with the charge and parity mixing,…