International Journal of Modern Physics E

The current status of the physics of massive neutrinos is reviewed with a forward-looking emphasis. The article begins with the general phenomenology of neutrino oscillations in vacuum and matter and documents the experimental evidence for oscillations of solar, reactor, atmospheric and accelerator neutrinos. Both active and sterile oscillation possibilities are considered. The impact of cosmology (BBN, CMB, leptogenesis) and astrophysics (supernovae, highest energy cosmic rays) on neutrino observables and vice versa, is evaluated. The predictions of grand unified, radiative and other models of neutrino mass are discussed. Ways of determining the unknown parameters of three-neutrino oscillations are assessed, taking into account eight-fold degeneracies in parameters that yield the same oscillation probabilities, as well as ways to determine the absolute neutrino mass scale (from beta-decay, neutrinoless double-beta decay, large scale structure and Z-bursts). Critical unknowns at present are the amplitude of ν_μ→ν_e oscillations and the hierarchy of the neutrino mass spectrum; the detection of CP violation in the neutrino sector depends on these and on an unknown phase. The estimated neutrino parameter sensitivities at future facilities (reactors, superbeams, neutrino factories) are given. The overall agenda of a future neutrino physics program to construct a bottom-up understanding of the lepton sector is presented.

We investigate the conditions under which particle multiplicities in high energy collisions are Boltzmann distributed, as is the case for hadron production in e⁺e^-, pp, and heavy ion collisions. We show that the apparent temperature governing this distribution does not necessarily imply equilibrium (thermal or chemical) in the usual sense. We discuss an explicit example using tree level amplitudes for N photon production in which a Boltzmann-like distribution is obtained without any equilibration. We argue that the failure of statistical techniques based on free particle ensembles may provide a signal for collective phenomena (such as large shifts in masses and widths of resonances) related to the QCD phase transition.

Recently, long-lived high spin super- and hyperdeformed isomeric states with unusual radioactive decay properties have been discovered. Based on these newly observed modes of radioactive decay, consistent interpretations are suggested for previously unexplained phenomena seen in nature. These are the Po halos, the low-energy enhanced 4.5 MeV α-particle group proposed to be due to an isotope of a superheavy element with Z=108, and the giant halos.

The effect of the non-extensive form of statistical mechanics proposed by Tsallis on the formation of a quark-gluon plasma (QGP) has been recently investigated in Ref. 1. The results show that for small deviations (≈ 10%) from Boltzmann–Gibbs (BG) statistics in the QGP phase, the critical temperature for the formation of a QGP does not change substantially for a large variation of the chemical potential. In the present paper we use the extensive κ-deformed statistical mechanics constructed by Kaniadakis to represent the constituents of the QGP and compare the results with Ref. 1.

We study the hydrodynamics of the nuclear matter of two flavors of light quarks with spontaneous chiral symmetry breaking based on the Poisson bracket method. The effects of mass are included and the full hydrodynamic equation for pions is given. The in-medium dispersion relation of pions in the neutron rich background state and the possibility of the phase transition to pion condensation are also discussed.

Rotationally single-particle and vibrational excitations of deformable odd non-axial odd nuclei are investigated with allowance for the interaction of collective and single-particle states. The ratios of excitation energies, of reduced probabilities of E2 transitions, and of quadrupole moments for deformable non-axial odd nuclei are calculated up to high-spin states.

The effect of the exchange terms in nucleon-nucleon interaction is studied for nuclear matter and neutron matter in the framework of the hybrid derivative coupling model. Pseudovector coupling between the pion and the nucleon and both vector and tensor couplings between the rho-meson and the nucleon have been included. A reduced value of the effective nucleon mass is obtained in nuclear matter as a result of the inclusion of the exchange terms. The rho-meson coupling constant obtained from meson exchange theories can be used to get a reasonable value of symmetry energy. The maximum limit of the neutron star mass obtained in this work is more than twice the solar mass. This rather high limit points to the inadequacy of the present Lagrangian at such a high density as it is restricted only to nucleonic degrees of freedom.

The experimental results of space, azimuthal, and projected angular distributions of target black fragments produced in silicon-emulsion collisions at 4.5A GeV/c (the Dubna energy) are reported. A multi-source ideal gas model is suggested to describe the experimental angular distributions. The Monte Carlo calculated results are in agreement with the experimental data.

The ground state nucleon (neutron and proton) distributions for A=20 isobars (Z=6–12) are investigated. For this purpose, the relativistic mean field equations are solved in the coordinate space and also by using the conventional basis expansion method. The pairing is treated in the simple constant gap approximation and also self consistently through the Bogoliubov transformation employing the realistic Gogny D1S interaction as well as the zero range density dependent effective interaction. The comparative study of the results thus obtained indicates the level and the extent of differences in the physical observables like binding energies, sizes, densities, etc. of these nuclei, arising due to the use of these different variants of solving the RMF/RHB equations. Though the results are qualitatively similar, the deviations do appear at a finer level, especially for large T_z (²⁰O and ²⁰N). The calculations also reveal mirror symmetry about T_z=0 for all physical observables, which is in accordance with the experiment. The calculated nucleon densities are compared with those obtained by using a semi-phenomenological model that incorporates correctly the asymptotic behavior. The reaction cross-sections with these A=20 isobars as projectiles incident on a ¹²C target at 950 A MeV incident energy, calculated within the Glauber model using the RMF/RHB and model densities agree well with the experiment.