Abstract:
Parity violating (PV) contributions due to interference between $\gamma$ and $Z^0$ exchange are calculated for pion electroproduction off the nucleon. A phenomenological model with effective Lagrangians is used to determine the resulting asymmetry for the energy region between threshold and $\Delta(1232)$ resonance. The $\Delta$ resonance is treated as a Rarita-Schwinger field with phenomenological $N \Delta$ transition currents. The background contributions are given by the usual Born terms using the pseudovector $\pi N$ Lagrangian. Numerical results for the asymmetry are presented.

Abstract:
Threshold neutral pion electroproduction on the deuteron is studied in the framework of baryon chiral perturbation theory at next-to-leading order in the chiral expansion. To this order in small momenta, the amplitude is finite and a sum of two- and three-body interactions with no undetermined parameters. We calculate the S-wave multipoles for threshold production and the deuteron S-wave cross section as a function of the photon virtuality. We also discuss the sensitivity to the elementary neutron amplitudes.

Abstract:
By introducing electromagnetic formfactors in the spacelike region we extend an effective, gauge invariant Lagrangian model considering Born terms, baryon resonances up to 1.7 GeV and vector meson contributions (Rho, Omega) to calculate electroproduction of Pi-mesons. This model forms the basis for predictions of pion induced dilepton production on the nucleon. Therefore, the implemented formfactors are constructed in such a way that their analytic continuation into the timelike region is possible. It is shown that the seagull term and the N*(1520) resonance play a dominant role in the dilepton production.

Abstract:
We develop a Lorenz- and gauge-invariant dynamical model for pion electroproduction in the resonance region. The model is based on solving of the Salpeter (instantaneous) equation for the pion-nucleon interaction with a hadron-exchange potential. We find that the one-particle-exchange kernel of the Salpeter equation for pion electroproduction develops an unphysical singularity for a finite value of $Q^{2}$. We analyse two methods of dealing with this problem. Results of our model are compared with recent single-polarization data for pion electroproduction.

Abstract:
The neutral pion electroproduction on the proton is considered in the framework phenomenological model based on the PCAC, current algebra with hard pions and chiral symmetry breaking interaction. The s- wave differential cross-section of the electroproduction of neutral pions off protons near the threshold is predicted as function photon momentum transfer squared $k^2$ . The s- wave multipoles $ReE_{0+}$ and $ReL_{0+}$ as function of the energy of the $\pi^0p$- system are given for the small $k^2$ and $% k^2=0.1(GeV/c)^2$. The results are compered with the experiment. It is shown the significant role of the explicit chiral symmetry breaking.

Abstract:
We report the measurement of near threshold neutral pion electroproduction cross sections and the extraction of the associated structure functions on the proton in the kinematic range $Q^2$ from 2 to 4.5 GeV$^2$ and $W$ from 1.08 to 1.16 GeV. These measurements allow us to access the dominant pion-nucleon s-wave multipoles $E_{0+}$ and $S_{0+}$ in the near-threshold region. In the light-cone sum-rule framework (LCSR), these multipoles are related to the generalized form factors $G_1^{\pi^0 p}(Q^2)$ and $G_2^{\pi^0 p}(Q^2)$. The data are compared to these generalized form factors and the results for $G_1^{\pi^0 p}(Q^2)$ are found to be in good agreement with the LCSR predictions, but the level of agreement with $G_2^{\pi^0 p}(Q^2)$ is poor.

Abstract:
Near threshold neutral pion electroproduction on the deuteron is studied in the framework of baryon chiral perturbation theory at next-to-leading order in the chiral expansion. We develop the multipole decomposition for pion production off spin-1 particles appropriate for the threshold region. The existing data at photon virtuality k^2 = -0.1 GeV^2 can be described satisfactorily. Furthermore, the prediction for the S-wave multipole E_d at the photon point is in good agreement with the data.

Abstract:
Baryon to meson transition distribution amplitudes (TDAs), non-diagonal matrix elements of the nonlocal three quark operator between a nucleon and a meson state, extend the concept of generalized parton distributions. These non-perturbative objects which encode the information on three quark correlations inside the nucleon may be accessed experimentally in backward meson electroproduction reactions. We suggest a general framework for modelling nucleon to pion (pi N) TDAs employing the spectral representation for pi N TDAs in terms of quadruple distributions. The factorized Ansatz for quadruple distributions with input from the soft-pion theorem for pi N TDAs is proposed. It is to be complemented with a D-term like contribution from the nucleon exchange in the cross channel. We present our estimates of the unpolarized cross section and of the transverse target single spin asymmetry for backward pion electroproduction within the QCD collinear factorization approach in which the non-perturbative part of the amplitude involves pi N TDAs. The cross section is sizable enough to be studied in high luminosity experiments such as J-lab@12GeV and EIC.

Abstract:
Near threshold neutral pion electroproduction on the deuteron is studied in the framework of heavy baryon chiral perturbation theory. We include the next-to-leading order corrections to the three-body contributions. We find an improved description of the total and differential cross section data measured at MAMI. We also obtain more precise values for the threshold S-wave multipoles. We discuss in detail the theoretical uncertainties of the calculation.

Abstract:
We present predictions for the spin structure functions of the proton and the neutron in the framework of a unitary isobar model for one-pion photo- and electroproduction. Our results are compared with recent experimental data from SLAC. The first moments of the calculated structure functions fulfill the Gerasimov-Drell-Hearn and Burkhardt-Cottingham sum rules within an error of typically 5-10% for the proton. For the neutron target we find much bigger deviations, in particular the sum rule for I_1(0)+I_2(0) is heavily violated.