Search

We investigate the cross section for the reaction NN → NNa₀ near the threshold and at medium energies. An effective Lagrangian approach with a one-pion exchange is applied to analyse different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also considered. The results are used to calculate the contribution of the a₀ meson to the cross sections and invariant K &barK; mass distributions of the reactions pp → pnK⁺&barK;⁰ and pp → ppK⁺K⁻. We found that the experimental observation of a⁺₀ mesons in the reaction pp → pnK⁺ &barK;⁰ is much more promising than the observation of a⁰₀ mesons in the reaction pp → pp K⁺K⁻.

The connection between light-cone dynamics and field theory is analyzed in detail within the zero-range approximation, with particular attention to the so-called “angular condition”. New and detailed calculations for the elastic form factors of the deuteron are presented for the Bonn, Paris, Reid Soft-Core, Argonne V14 and one-pion-exchange potentials with various choices of the electromagnetic form factors of the nucleon.

The relativistic correction to the triton binding energy approximated to the order (v/c)2 is calculated in the framework of relativistic Hamiltonian dynamics. We discuss the generator representation of the Poincaré group for three relativistic particles and its connection with the Feynman diagrams in the infinite-momentum frame (the light-front dynamics). The relativistic correction enhances the attraction in the three-nucleon system. The five-channel calculation with the Reid soft-core potential yeilds the result ?e=-0.54 MeV, which is governed mainly by theD-wave contribution. TheS-wave contributions to ?e are only -0.10 MeV.

A new procedure is devised to evaluate the proton form-factor at the ¯pp threshold from experimental data on ¯pp→e+e− annihilation at rest. Comparison of the ¯pp→e+e− and¯pp→π+π− processes reveals that annihilation ranges for various channels are ranked in line with quark dynamics.

The effects of superconductivity of the quark matter in SU(2) colour group are studied. We analyze the QCD-inspired model of interaction of the quarks with the four quark contact interaction which represents relativistic extension of the BCS model. We construct, using the Gor'kov's propagator approach to description of the superconductivity, explicit expressions for the quark propagator, for the anomalous Green's functions, discuss their transformation properties, transformation properties of the order parameters, and find dispersion laws for quasiparticle modes in the one flavour quark matter. There exist two types of solutions of the superconductivity equations corresponding to condensation of the quark Cooper pairs in the triplet spin state. We show that the gap function depends on directions of the quasiparticle momentum and in the massless limit the energy gap vanishes for some directions of the momentum. We estimate the order parameters and critical temperaturs of the phase transition from the normal to the superconducting state, and give expressions for the fermion number density and spin density in the two states of the quark matter. We discuss also analogy between the superconducting quark matter and the nuclear matter in the case of SU(2) colour group. Two quarks in colourless state in SU(2) colour group carry fermion number and should therefore be identified with baryons, so the Cooper pairs in the quark matter can be considered as a kind of baryons present in the quark matter. The superconducting quark matter can be considered as a mixture of quarks and baryons. Such a type of the baryonic matter is shown to obey saturation condition — the well known property of nuclear matter in the real world. The possibility of extension of the model considered to the SU(3) colour group is discussed.

Effects related to the possible admixture of multiquark (mainly 12q) clusters (bags) in nuclei are discussed. In particular the differencies in theu- andd-quark distributions inN?Znuclei are considered. The quark distribution function is assumed to consist of two components: the nucleon component and the bag one (mainly the 12q-bag). The yields ofp-mesons and nucleons into the backward hemisphere are governed mainly by the contribution of the bag component. It comes from the available data on thep+/p- andn/p ratios that thed-quarks in the bag component of nuclei withN>Z are “more soft” than theu-quarks in contrast to the situation in the nucleon component. The manifestation of the latter effect in theA-dependence of the ratio of structure functionsR=F2A(x)/F2D(x) is also discussed.

Inclusivep, d and3He cross sections have been obtained using experimental data on p4He collisions over an incident proton energy range of 46-400 GeV. Considering the slopes of spectra, the effective nuclear temperature has been found to be T0=11 MeV, which is in good agreement with experimental results for lower energies and heavier targets. The shape of the3He inclusive spectrum suggests the existence of two different3He production mechanisms. The experimental3He cross section is compared with theoretical predictions assuming fragment formation as a result of the spectator and cluster knockout mechanisms. The4He?3He +n vertex constant has been found to be G2=10.9±0.2 fm.

We start from a field-theoretical model of zero range approximation to derive three-dimensional relativistic two- and three-body equations on a null plane. We generalize those equations to finite range interactions. We propose a three-body null-plane equation whose form is different from the one presented earlier in the framework of light-cone dynamics. We discuss the choices of the kernels in two- and three-body cases and apply our model to the description of meson and baryon Regge trajectories. Our approach overcomes some theoretical and phenomenological difficulties met in preceding relativized treatments of the three-body problem.

Low temperature of the phase transition into the quark-gluon plasma correspond to low values of the bag model constant and to absolutely stable strange quark matter. Some of the observed pulsars are identified quite reliably as neutron stars. If strange matter is stable, the central density of these pulsars is to be smaller that critical density of the phase transition into the nonstrange quark matter. The nonstrange quark matter being formed turns to more stable strange matter on a weak interaction timescale converting neutron stars into strange stars. The requirement of stability of old and newly born neutron stars is used to constrain the bag model constant and the critical temperature of the phase transition into the quark-gluon plasma at zero chemical potential.