arXiv subjects

M. I. Krivoruchenko

Publications and source records attributed to M. I. Krivoruchenko.

85 records · Page 5Linked to original sources

arXiv1998

D' Production in Heavy Ion Collisions

The production of d' dibaryons in heavy ion collisions due to the elementary process NN -> d' + pion is considered. The cross section NN -> d' + pion is estimated using the vacuum d' width = 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d' production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NN + pion system in order to search for an abundance of events with the invariant mass of the d' dibaryon. The d' peak is found to exceed the statistical fluctuations of the background at a level of 6 standard deviations for 2 10^5 A central collisions of heavy ions with the atomic number A.

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arXiv1997

Analytical Extension of the Frazer-Fulco Unitarity Relations for Isovector Nucleon Form Factors to the Complex t-Plane

The unitarity relations for isovector nucleon form factors in the two-pion approximation for the intermediate states are analytically extended in a model independent way from the real half-axis t > 4 $μ^2$ ($μ$ is the pion mass) to the whole complex t-plane. As a result, the explicit integral representations for the nucleon form factors are constructed in terms of the pion form factor and imaginary parts of the t-channel p-wave piN-scattering amplitudes at t < 0. New method based on the explicit integral representations is developed for numerical evaluation of the two-pion contribution to the isovector nucleon form factors. The results of different methods are compared and their efficiency is discussed.

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arXiv1997

Dibaryons in nuclear matter

The possibility for occurrence of a Bose condensate of dibaryons in nuclear matter is investigated within the framework of the Walecka model in the mean-field approximation. Constraints for the omega - and sigma - meson coupling constants with dibaryons following from the requirement of stability of dibaryon matter against compression are derived and the effect of sigma - and pi - meson exchange current contributions to the sigma - dibaryon coupling constant is discussed. The mean-field solutions of the model are constructed. The effective nucleon mass vanishes when the density of dibaryons approaches a critical value about 0.15/fm^3. The Green's functions of the equilibrium binary mixture of nucleons and dibaryons are constructed by solving the Gorkov-Dyson system of equations in the no-loop approximation. We find that when the square of the sound velocity is positive, the dispersion laws for all elementary excitations of the system are real functions. This indicates stability of the ground state of the heterophase nucleon-dibaryon mixture. In the model considered, production of dibaryons becomes energetically favorable at higher densities as compared to estimates based on a model of non-interacting nucleons and dibaryons.

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arXiv1997

Nuclear matter with a Bose condensate of dibaryons in relativistic Hartree approximation

The Green's functions are constructed and a one-loop calculation is given for the scalar and vector densities and for the equation of state of nuclear matter with a Bose condensate of dibaryons. This is the lowest approximation in the loop expansion of quantum hadrodynamics, sufficient to account for the presence of dibaryons not in the condensate in the heterophase nucleon-dibaryon matter. It leads to a finite effective nucleon mass and remains consistent with increasing the density.

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arXiv1997

Condensation of Dibaryons in Nuclear Matter and Its Possible Signatures in Heavy Ion Collisions

We consider the thermodynamics of the matter made up of equal number of neutrons and protons and of scalar dibaryons. They interact via the exchange of scalar and vector mesons. The interaction is taken into account in the mean field approximation. The condensation of dibaryons in this matter and the phase transition of matter to quark matter are considered. Possible signatures of dibaryons in Heavy Ion Collisions are speculated on.

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arXiv1997

Constraints to Coupling Constants of the Omega- and Sigma-Mesons with Dibaryons

The effect of narrow dibaryon resonances to nuclear matter and structure of neutron stars is investigated in the mean-field theory (MFT) and in the relativistic Hartree approximation (RHA). The existence of massive neutron stars imposes constraints to the coupling constants of the omega- and sigma-mesons with dibaryons. We conclude that the experimental candidates to dibaryons d1(1920) and d'(2060) if exist form in nuclear matter a Bose condensate stable against compression. This proves stability of the ground state for nuclear matter with a Bose condensate of the light dibaryons.

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arXiv1997

Resonance Production on Nuclei at High Energies: Nuclear-Medium Effects and Space-Time Picture

The influence of nuclear matter on the properties of coherently produced resonances is discussed. It is shown that, in general, the mass distribution of resonance decay products has a two-component structure corresponding to decay outside and inside the nucleus. The first (narrow) component of the amplitude has a Breit-Wigner form determined by the vacuum values of mass and width of the resonance. The second (broad) component corresponds to interactions of the resonance with the nuclear medium. It can be also described by a Breit-Wigner shape with parameters depending e.g. on the nuclear density and on the cross section of the resonance-nucleon interaction. The resonance production is examined both at intermediate energies, where interactions with the nucleus can be considered as a series of successive local rescatterings, and at high energies, $E>E_{crit}$, where a change of interaction picture occurs. This change of mechanisms of the interactions with the nucleus is typical for the description within the Regge theory approach and is connected with the nonlocal nature of the reggeon interaction.

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arXiv1996

Explicit Solutions to the Unitarity Relations for Isovector Nucleon Form Factors

The explicit one-dimensional integral representations for isovector nucleon form factors are constructed by solving the unitarity relations in terms of the pion form factor and imaginary parts of the t-channel p-wave $πN$-scattering amplitudes. The possibility of computation of the high-energy parts of the integrals with the use of the information on the low-energy real parts of the $πN$-scattering amplitudes is discussed.

hep-ph↗

arXiv1996

Nuclear Matter with a Bose Condensate of Dibaryons in Relativistic Mean-Field Theory

If sufficiently light dibaryon resonances exist, a Bose condensate of dibaryons can occur in nuclear matter before the quark-hadron phase transition. Within a relativistic mean-field model we show that heterophase nuclear-dibaryon matter is for a wide set of parameters energetically more favorable than normal nuclear matter. Production of dibaryons is, however, relatively suppressed as compared to estimates based on the model of non-interacting nucleons and dibaryons.

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arXiv1996

Dibaryon Condensate in Nuclear Matter and Neutron Stars: Exact Analysis in One-Dimensional Models

We investigate dense nuclear matter with a dibaryon Bose-Einstein condensate as a possible intermediate state before the quark-gluon phase transition. An exact analysis of this state of matter is presented in a one-dimensional model. The analysis is based on a reduction of the quantization rules for the N-body problem to N coupled algebraic transcendental equations. We observe that when the Fermi momentum approaches the resonance momentum, the one-particle distribution function increases near the Fermi surface. When the Fermi momentum is increased beyond the resonance momentum, the equation of state becomes softer. The observed behavior can be interpreted in terms of formation of a Bose-Einstein condensate of two-fermion resonances (dibaryons). In cold nuclear matter, it should occur if 2(m_N + epsilon_F) is greater or equal to m_D, where m_N and m_D are respectively the nucleon and dibaryon masses and epsilon_F is the nucleon Fermi energy.

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arXiv1996

Density dependence of resonance broadening and shadowing effects in nuclear photoabsorption

Medium effects as a function of the mass number $A$ are studied in the total photonuclear cross section from the $Δ$-resonance region up to the region where shadowing effects are known to exist. A consistent picture is obtained by simply assuming a density dependence of the different mechanisms of resonance broadening and shadowing. The $Δ$-mass shift is found to increase with $A$.

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arXiv1995

A Constraint to the Parity-Conserving Parameter of the Neutron-Antineutron Oscillations

The phenomenology of neutrino oscillations is extended to the neutron- antineutron oscillations predicted by the grand unified theories. There are six parameters in general describing the one-flavor oscillations: two real Majorana masses (of opposite signs), three Euler's angles, and a phase multiplier "chi". The sum of the Majorana masses, treated as a small parity- violating parameter "epsilon", induces the nuclear decays (A,Z) -> (A-2,Z) and determines the oscillation rate of neutrons in the vacuum. We derive a constraint to a small parity-conserving parameter "epsilon-prime" representing a combination of two Euler's angles. This parameter gives no significant contribution to the neutron oscillation rate in the vacuum, while contributes to the nuclear decay rate. The nuclear stability implies "epsilon-prime" < 1/year. Absence of the vacuum neutron oscillations together with existence of the nuclear decays (A,Z) -> (A-2,Z) would become simplest manifestation of the "epsilon-prime" =/ 0.

hep-ph↗

arXiv1995

SUPPRESSION OF THE NEUTRON-ANTINEUTRON OSCILLATION IN NUCLEI

The problem of nuclear decays occurring due to the neutron-antineutron oscillation is analyzed in the optical potentil model and within the field-theoretic S-matrix approach. The result of the optical potential model is rederived within the field theoretic S-matrix approach. The neutron- antineutron oscillation in nuclei is suppressed drastically. We discuss an example for the spin precession of an atom in which analogous suppression takes place due to transparent physical reasons.

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