International Journal of Modern Physics E

We study the properties of neutron stars adopting relativistic equations of state of neutron star matter, calculated in the framework of the relativistic Brueckner–Hartree–Fock approximation for electrically charge neutral neutron star matter in beta–equilibrium. For higher densities more baryons (hyperons etc.) are included by means of the relativistic Hartree– or Hartree–Fock approximation. The special features of the different approximations and compositions are discussed in detail. Besides standard neutron star properties special emphasis is put on the limiting periods of neutron stars, for which the Kepler criterion and gravitation–reaction instabilities are considered. Furthermore the cooling behaviour of neutron stars is investigated, too. For comparison we also give the outcome for some nonrelativistic equations of state.

We report the results on partial production cross sections for Z=2 projectile fragments emitted in ²⁸Si-emulsion interactions at 3.7 A GeV. Scaling behaviour of the multiplicity distribution of Z=2 PFs has been checked. The emission angle of Z=2 PFs has been measured and pseudorapidity distributions for these PFs have been obtained. We observe that the value of momentum spread σ(p) for Z=2 PFs grows with increasing mass number of the projectile. The emission of Z=2 PFs is consistent with a single source with an excitation energy of about 8.9 MeV. The data has been compared with available data reported for lighter as well as heavier projectiles at the same and/or different energies.

Spin-independent relativistic effect on binding and dissociation of heavy quarkonium in a thermal environment is stressed. The calculated result shows that the effect considerably influences the spin-averaged thermal properties of the system. As a result, it should be considered in future experiments at RHIC.

The charge densities of the nuclei ²⁰⁵Tl, ^206,208Pb have been calculated in modified shell model with fractional number occupations of the shell states 2s, 2p, 2d, and 3s. The value of the n_3s was found to be 0.6 for ²⁰⁶TI, and ≈ 1 for ^206,208Pb. These values differ appreciably from other data which range between 1.3 to 1.6. By addition of the two neutrons to ²⁰⁶P a charge of 0.24e of one proton is moved from the inner region of the ²⁰⁸Pb to the outer region. In the context of our modified shell model calculations, the measured charge density and occupancy profiles imply that the neutron degrees of freedom we employ carry charge.

The quon algebra, which interpolates between the Bose and Fermi algebras and depends on a free paramenter q, is used to generate a deformed Dyson boson expansion of the quadrupole operator. Then we obtain a quadrupole-quadrupole hamiltonian, for a single j-shell, in terms of this deformed bosonic operator. The hamiltonian is diagonalized and its eigenvalues are compared with the ones obtained from the fermionic quadrupole-quadrupole hamiltonian. The deformation parameter helps in achieving the correct excitation energy levels, what cannot be encountered in practice with the usual non-deformed Dyson expansion.

Neutron rich nuclei in the medium mass region with thermal excitation and rotational energies, are investigated. A macroscopic-microscopic approach to reproduce the ground state separation energy combined with statistical approach for the excited rotating nuclei yields good results. Shell effects and shape transitions due to rotation alter the boundary of the drip line considerably at low temperatures and with increasing temperature the drip line is lowered to less neutron rich nuclei.

To date, no evidence of ββ0ν decay has been found despite tremendous experimental efforts. In contrast, ββ2ν decay has been clearly and definitely observed in several nuclei. These experimental facts question the reality of ββ0ν decay. This ββ0ν decay which violates lepton number conservation can only occur if the neutrino is massive and is its own antiparticle or in other words is a truly neutral particle. The observation of this decay implies then that the neutrino is a truly neutral particle and it has a non-zero mass. But the absence of ββ0ν decay implies only that at least one of the two necessary conditions is not fulfilled. Since the truly neutral character of neutrino is a necessary condition, it is important to provide objective criteria of truly neutral particles. We propose a generalized Gell-Mann and Nishijima formula which provides naturally the criteria of truly neutral particles. According to these criteria n and ν are different from their antiparticles for symmetric reason. The absence of ββ0ν decay could then be simply understood. Indeed a truly neutral particle could be more generally defined as a neutral particle with respect to all charges and is its own antiparticle. The Dirac character of the neutrino does not contradict any experimental fact.

We estimate the phase diagram for nuclear matter described by a Skyrme-type momentum dependent interaction and compare the results with that for a potential with no momentum dependence. It is shown that the momentum dependence decreases the critical temperatures.