A. Yu. Loginov

Effect of rescattering on polarization observables of the reaction γd → ppπ in the delta-resonance region

The effect of pion-nucleon and nucleon-nucleon rescatterings on polarization observables of the reaction γd → ppπ− are calculated in the delta-isobar region. Pion-nucleon and nucleon-nucleon rescatterings are considered on the basis of a diagrammatic approach. Lorentz invariant expressions are used for the operators of photoproduction and of pion scattering on a free nucleon. A unitarization procedure in the K-matrix approximation is used for resonance partial-wave amplitudes. It is shown that, in the delta-resonance region, rescattering has a sizable effect on polarization observables of the reaction γd → ppπ− at high momenta of final protons.Influence of the effects of the pion-nucleon and nucleon-nucleon re-scattering on the polarization observables of the reaction gamma + d = p + p + pi- in Delta - isobar region is investigated. Pion-nucleon and nucleon-nucleon re-scattering are studied in the diagrammatic approach. Relativistic-invariant forms of the pion photoproduction and pion-nucleon scattering operators are used. The unitarization procedure in K-matrix approach is applied for the resonance partial amplitudes. It is shown a considerable influence of the re-scattering effects on the polarization observables of this reaction in the Delta - resonance region for the large momenta of the final protons.

Investigation of the reaction D(e, pp)e′ π− on a tensorpolarized deuterium target at high proton momenta

The differential cross section of the reaction D(e,pp)e′ π− is measured in the range of proton momenta 300–720 MeV/c and proton emergence angles 64–83° for invariant masses of the pp system ranging from 2mp to 2220 MeV/c2. The measured values of the cross section are found to differ substantially from single-particle model calculations. The components of the analyzing power for this reaction are measured.

Rotating skyrmions of the (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term

The (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term is considered. The presence of the Chern-Simons term makes possible the existence of two-dimensional skyrmions in this model, which carry magnetic flux and have an electric charge and a nonzero angular momentum. It is shown that the model also admits the existence of two-dimensional skyrmions with a nonzero phase frequency of rotation. Due to the nontrivial topological properties of the model, the magnetic flux, the electric charge, and the angular momentum of a two-dimensional rotating skyrmion turn out to be interrelated. Analytic and numerical investigations of the properties of rotating two-dimensional skyrmions are carried out.

Measurement of the components of the tensor analyzing power in the reaction γd → ppπ − at high proton momenta

Results obtained by measuring three components of the tensor analyzing power in the reaction of π− -meson photoproduction on a deuteron at final-proton momenta between 300 and 700 MeV/c are presented. The measurements in question were performed at the VEPP-3 storage ring by using its internal deuterium-gas target featuring a tensor polarization with the aid of detection of two protons in coincidence. The experimental results obtained in this way are compared with their counterparts calculated theoretically.

Q kink of the nonlinear O(3) σ model involving an explicitly broken symmetry

The (1 + 1)-dimensional nonlinear O(3) σ model involving an explicitly broken symmetry is considered. Sphalerons are known to exist in this model. These sphalerons are of a topological origin and are embedded kinks of the sine-Gordon model. In the case of a compact spatial manifold S1, sine-Gordon multikinks exist in the model. It is shown that the model admits a nonstatic generalization of the sine-Gordon kink/multikink, Q kink/multikink. Explicit expressions are obtained for the dependence of the Q kink energy and charge on the phase frequency of rotation. The Q kink is studied for stability, and expressions are obtained for the eigenfunctions and eigenfrequencies of the operator of quadratic fluctuations. It is shown that the Q kink is unstable over the entire admissible frequency range ω ∈ [−1, 1]. The one-loop quantum correction to the static-kink mass is calculated, and the Q-kink zero mode is quantized. It is shown that, in a general static case, the field equations of the model are integrable in quadratures.

Photoreactions with tensor-polarized deuterium target at VEPP–3

We give an overview of the activity in studying photoprocesses on a tensor-polarized deuterium target, which is carried out at the VEPP–3 electron storage ring. Recent experimental results on tensor asymmetries in two-body deuteron photodisintegration at the photon energy up to 500 MeV, and in coherent pion photoproduction on deuteron are presented. Plans to upgrade the facility and future experiments are discussed. Further progress is connected with the installation of a tagging system for almost-real photons. This would allow us to extend the measurements of polarization observables in photonuclear reactions on deuteron up to a photon energy of 1.5 GeV and permit to perform double polarized experiments – with linear polarized photon beams and tensor/vector polarized deuterium targets.

Tensor asymmetry of π−-meson photoproduction on polarized deuterons

The tensor asymmetry of exclusive π−-meson photoproduction on polarized deuterons was investigated. The T20 and T22 components of the reaction analyzing power contribute to the measured asymmetry. The detector made it possible to record two outgoing protons in coincidence in the range of polar angles θ1,2 = 44° − 88° and in the momentum range p1,2 = 350 − 700 MeV c−1. The measurements were performed at the VEPP-3 storage ring (Novosibirsk) using an internal target. The experimental results are compared with theoretical calculations.

A two-dimensional soliton system of vortex and Q-ball

Abstract The ( 2 + 1 ) -dimensional gauge model describing two complex scalar fields that interact through a common Abelian gauge field is considered. It is shown that the model has a soliton solution that describes a system consisting of a vortex and a Q-ball. This two-dimensional system is electrically neutral, nevertheless it possesses a nonzero electric field. Moreover, the soliton system has a quantized magnetic flux and a nonzero angular momentum. Properties of this vortex-Q-ball system are investigated by analytical and numerical methods. It is found that the system combines properties of topological and nontopological solitons.

Bound fermion states in the field of a soliton of the nonlinear O (3) σ model

The (2 + 1)-dimensional nonlinear O(3) σ model whose n field is coupled to the fermion field by the Yukawa interaction has been examined. The cases of the isosinglet and isodoublet fermion fields with respect to the internal symmetry group have been considered. It has been shown that bound states of the fermion in the n field of a soliton of the nonlinear O(3) σ model exist for some variants of the Yukawa interaction. The absence of zeroth fermion modes in the n field of the soliton has been established. The properties of the ground state of the fermion have been numerically studied. In particular, it has been shown that an increase in the spatial size of the soliton results in a decrease in the energy of the ground state. This leads to the instability of the soliton in a certain region of the parameters of the model.

Tensor analyzing power component T21 of a π−-meson in the photoproduction on a deuteron

The preliminary results of measurement of the tensor analyzing power component, T21 of negative pion photoproduction on a polarized deuterons at photon energies of 280 MeV – 900 MeV, and in the pion emission angles of 0° – 180° are presented. The experimental results are compared with the theoretical predictions.