\bar{p}p low energy parameters from annihilation cross section data

The recent experimental data obtained by the OBELIX group on total $\bar{p}p$ annihilation cross section are analysed; the low energy spin averaged parameters of the $\bar{p}p$ scattering amplitude (the imaginary parts of the S-wave scattering length and P-wave scattering volume) are extracted from the data. Their values are found to be equal to $Im a_{sc} = - 0.69 \pm 0.01 (stat) \pm 0.03 (sys) fm, Im A_{sc} = - 0.76 \pm 0.05 (stat) \pm 0.04 (sys) fm^3$. The results are in very good agreement with existing atomic data.Comment: latex.tar.gz file, 8 pages, 1 figur

Solution of the Bethe-Salpeter equation in Minkowski space for a two fermion system

The method of solving the Bethe-Salpeter equation in Minkowski space, developed previously for spinless particles, is extended to a system of two fermions. The method is based on the Nakanishi integral representation of the amplitude and on projecting the equation on the light-front plane. The singularities in the projected two-fermion kernel are regularized without modifying the original BS amplitudes. The numerical solutions for the J=0 bound state with the scalar, pseudoscalar and massless vector exchange kernels are found. Binding energies are in close agreement with the Euclidean results. Corresponding amplitudes in Minkowski space are obtained.Comment: 8 pages, 5 figures. Contribution to the proceedings of the Workshop: Light-Cone 2010, "Relativistic Hadronic and Particle Physics", June 14-18, 2010, Valencia, Spain. To be published in the online journal "Proceedings of Science" - Po

Solving Bethe-Salpeter equation for two fermions in Minkowski space

The method of solving the Bethe-Salpeter equation in Minkowski space, which we developed previously for spinless particles, is extended to a system of two fermions. The method is based on the Nakanishi integral representation of the amplitude and on projecting the equation on the light-front plane. The singularities in the projected two-fermion kernel are regularized without modifying the original Bethe-Salpeter amplitudes. The numerical solutions for the J=0 bound state with the scalar, pseudoscalar and massless vector exchange kernels are found. The stability of the scalar and positronium states without vertex form factor is discussed. Binding energies are in close agreement with the Euclidean results. Corresponding amplitudes in Minkowski space are obtained.Comment: 11 pages, 9 figures, to be published in Eur. Phys. J.

Solutions of the Bethe-Salpeter equation in Minkowski space and applications to electromagnetic form factors

We present a new method for solving the two-body Bethe-Salpeter equation in Minkowski space. It is based on the Nakanishi integral representation of the Bethe-Salpeter amplitude and on subsequent projection of the equation on the light-front plane. The method is valid for any kernel given by the irreducible Feynman graphs and for systems of spinless particles or fermions. The Bethe-Salpeter amplitudes in Minkowski space are obtained. The electromagnetic form factors are computed and compared to the Euclidean results.Comment: 20 pages, 14 figures, contribution to proceedings of the workshop: "Relativistic Description of Two- and Three-Body Systems in Nuclear Physics", ECT*, October 19-23, 2009. To be published in Few-Body System

Scattering states in Bethe-Salpeter equation

The off-mass shell scattering amplitude, satisfying the Bethe-Salpeter equation for spinless particles in Minkowski space with the ladder kernel, is computed for the first time.Comment: 7 pages, 3 figures. Presented at the XXI International Baldin Seminar on High Energy Physics Problems, September 10-15, 2012, JINR, Dubna, Russia. To be published in the online journal Proceedings of Science - PoS(Baldin ISHEPP XXI)027 (2012

Scattering solutions of Bethe-Salpeter equation in Minkowski and Euclidean spaces

We shortly review different methods to obtain the scattering solutions of the Bethe-Salpeter equation in Minkowski space. We emphasize the possibility to obtain the zero energy observables in terms of the Euclidean scattering amplitude.Comment: 7 pages, 2 figures, contribution to the conference Light-Cone 2015, Frascati, Italy, 21-25 September, 2015. Submitted in Few-Body System

Deuteron electromagnetic form factors in the Light-Front Dynamics

The deuteron form factors are calculated in the framework of the relativistic nucleon-meson dynamics, by means of the explicitly covariant light-front approach. The inflluence of the nucleon electromagnetic form factors is discussed. At $Q^2\leq 3$ (GeV/c)$^2$ the prediction for the structure function $A(Q^2)$ and for the tensor polarization observable $t_{20}$ are in agreement with the recent data of CEBAF/TJNAF.Comment: 1 latex.tar.gz file (18 pages, 8 figures in 11 .ps files) Submitted for publicatio

Bound state techniques to solve the multiparticle scattering problem

Solution of the scattering problem turns to be very difficult task both from the formal as well as from the computational point of view. If the last two decades have witnessed decisive progress in ab initio bound state calculations, rigorous solution of the scattering problem remains limited to A$\leq$4 case. Therefore there is a rising interest to apply bound-state-like methods to handle non-relativistic scattering problems. In this article the latest theoretical developments in this field are reviewed. Five fully rigorous methods will be discussed, which address the problem of nuclear collisions in full extent (including the break-up problem) at the same time avoiding treatment of the complicate boundary conditions or integral kernel singularities. These new developments allows to use modern bound-state techniques to advance significantly rigorous solution of the scattering problem.Comment: To appear in Progress in Particle and Nuclear Physic

Explicitly covariant light-front dynamics and some its applications

The light-front dynamics is an efficient approach to study of field theory and of relativistic composite systems (nuclei at relativistic relative nucleon momenta, hadrons in the quark models). The explicitly covariant version of this approach is briefly reviewed and illustrated by some applications.Comment: 16 pages, 8 figures. Talk at the 21-st International Workshop on Nuclear Theory, Rila Mountains, Bulgaria, June 10-15, 200