International Journal of Modern Physics E

Neutrinos are the only particles in the Standard Model (SM) of particle physics that have only been observed with left handed chirality to date. If right handed (RH) neutrinos exist, they could be responsible for several phenomena that have no explanation within the SM, including neutrino oscillations, the baryon asymmetry of the universe, dark matter (DM) and dark radiation (DR). After a pedagogical introduction, we review recent progress in the phenomenology of RH neutrinos. We in particular discuss the mass ranges suggested by hints for neutrino oscillation anomalies and DR (eV), sterile neutrino DM scenarios (keV) and experimentally testable theories of baryogenesis (GeV to TeV). We summarize constraints from theoretical considerations, laboratory experiments, astrophysics and cosmology for each of these.

The Drell–Yan process is an invaluable tool for probing the structure of hadrons, and the pion-induced Drell–Yan process is unique in its sensitivity to several subtleties of the partonic structure. This is a brief review of the pionic Drell–Yan process with particular emphasis on the dilepton angular distributions and nuclear modification of the parton distributions (the EMC effect).

By analyzing recent microscopic many-body calculations of few-nucleon systems and complex nuclei performed by different groups in terms of realistic nucleon–nucleon (NN) interactions, it is shown that NN short-range correlations (SRCs) have a universal character, in that the correlation hole that they produce in nuclei appears to be almost A-independent and similar to the correlation hole in the deuteron. The correlation hole creates high-momentum components, missing in a mean-field (MF) description and exhibiting several scaling properties and a peculiar spin–isospin structure. In particular, the momentum distribution of a pair of nucleons in spin–isospin state (ST) = (10), depending upon the pair relative (k_rel) and center-of-mass (c.m.) (K_c.m.) momenta, as well as upon the angle Θ between them, exhibits a remarkable property: in the region k_rel≳2 fm^-1 and K_c.m.≲1 fm^-1, the relative and c.m. motions are decoupled and the two-nucleon momentum distribution factorizes into the deuteron momentum distribution and an A-dependent momentum distribution describing the c.m. motion of the pair in the medium. The impact of these and other properties of one- and two-nucleon momentum distributions on various nuclear phenomena, on ab initio calculations in terms of low-momentum interactions, as well as on ongoing experimental investigations of SRCs, are briefly commented.

A four parameter formula has been applied to obtain the nuclear softness parameter (σ) for all the superdeformed (SD) bands observed in A = 190 mass region. The nuclear softness parameter values of most of the SD bands are found to be smaller than those of the normal deformed bands, implying more rigidity. The results of this work includes the variation of nuclear softness parameter against the gamma ray energy ratio R(I) = E_γ(I→(I-2))/E_γ((I-2)→(I-4)) of SD bands in A = 190 mass region. The variation of R(I) and the nuclear softness parameter of these SD bands are studied with the product of valence proton and neutron numbers (N_pN_n). The systematics also includes the variation of σ with the neutron number N. It is also found that the value of softness parameter of signature partner SD bands observed in A = 190 mass region is also the same. We present for the first time the study of softness parameter of SD bands with N_pN_n scheme.

In this paper, we use the lowest order constrained variational method to study the behavior of nuclear symmetry energy versus density and spin states of neutrons and protons with AV₁₈ potential. The dependency of incompressibility at saturation density on isospin asymmetry, ferromagnetic spin states and antiferromagnetic spin states is also investigated.

In this paper, yields of strange hadrons in relativistic heavy-ion collisions are investigated in the framework of the recombination model. Yield ratios of strange to nonstrange hadrons are studied. Strangeness enhancement is shown stronger for higher initial quark densities and for hadrons with more strange quarks.

New experimental data on cross-sections of yield of excited ⁶Li*, ⁷Li*, ⁹B* and ¹⁰B* nuclei and their contributions to formation of two nucleus (⁴He+²H), (⁴He+³H) and (⁴Li+²He) and three nucleus (⁴He +⁴H+¹H) systems in ¹⁶Op collisions at 3.25A GeV/c are presented.

This paper includes the experimental measurements for the angular distributions of ¹⁶O ion beam elastically scattered by ¹⁶O nuclei at energies 20, 24 and 28 MeV. The experimental results were analyzed within the framework of both the optical model using different complex potential and the double folding (DF) potential obtained with different density-dependent nucleon–nucleon interactions which give the corresponding values of the nuclear incompressibility K in the Hartree–Fock calculation of nuclear matter. The agreement between the experimental results and the theoretical predictions in the whole angular range is fairly good. In DF calculations, the obtained normalization coefficient N_r is in the range 0.833–1.07.

The effect of multiplicity correlation between two bins to the dynamical fluctuations is investigated for a second-order phase transition from quark–gluon plasma (QGP) to hadrons, within the Ginzburg–Landau description for the transition. Normalized factorial correlators are used to characterize the dynamical fluctuations. A scaling behavior among the correlators is found, and an approximate universal exponent is obtained with very weak dependence on the details of the phase transition.

The interaction strength between chiral doublet bands is studied using the two-band mixing picture and the particle rotor model (PRM). The present calculations indicate that the interaction strength between chiral doublet bands is equal to zero for the ideal case of the configuration with γ = 30°, and the interaction strength becomes larger as γ deviates from 30°. For γ = 15° or 45°, the average interaction strength is approximately 180 keV in the chiral region.

This paper studies the formation cross-sections of super heavy (SH) nuclei in some cold fusion reactions of radioactive neutron-rich projectiles with double-magic ²⁰⁸Pb target. In this study, the cross-sections of capture, fusion and evaporation residues in one- and two-neutron (1n and 2n) channels are calculated by using neutron-rich Fe, Ni and Zn projectiles are compared to the cross-sections calculated using stable Fe, Ni and Zn projectiles. The heights of fusion barrier and their positions in all reactions considered in this study are also compared to the heights and positions calculated using the estimation method proposed by Dutt and Puri. For cold fusion reactions with stable Fe, Ni and Zn projectiles, the heights of fusion barrier and the cross-sections of evaporation residues in 1n and 2n channels are compared to their corresponding experimental data. In general, for reactions using projectiles with the same proton number, the neutron-rich projectile is found to yield relatively-heavier mass of SH nucleus and larger evaporation residue cross-section, compared to those of the corresponding stable projectiles. However, in certain reactions, the cross-sections of neutron-rich projectile can be slightly larger or slightly smaller than that of the corresponding stable projectile. This behavior is highly affected by the charge of projectile and the fission barrier of the formed compound nucleus (CN). In addition, the ²⁹²114 is found to be the heaviest compound nucleus formed in cold fusion reaction by using neutron-rich nuclei as the projectile, but the cross-section of evaporation residue in one-neutron channel is still around few pico barns (pb).

By using the Nikiforov–Uvarov method, we give the approximate analytical solutions of the Dirac equation with the shifted Deng–Fan potential including the Yukawa-like tensor interaction under the spin and pseudospin symmetry conditions. After using an improved approximation scheme, we solved the resulting schrödinger-like equation analytically. Numerical results of the energy eigenvalues are also obtained, as expected, the tensor interaction removes degeneracies between spin and pseudospin doublets.

Muonic atoms formation in excited states is investigated. Using the two-state approximation (TSA), differential cross-sections for charge-transfer reaction as a(1s)+μ^-(a = H, D, T) collisions are calculated in the energy range from 0.001 eV to 1 eV. Our results indicate that the distribution of the principal quantum number n for captured muons has a peak around n = 14. It is also shown that the dependence of the differential cross-section on l diminishes with increase of energy. The results are in agreement with other calculations.

The anharmonity in shape transitional nuclei, observed earlier, is studied and an alternative form is derived. The dichotomy of a constant anharmonicity along with a changing nuclear structure is resolved. The evolution of the collective nuclear structure from the spherical vibrator to the deformed rotor is studied through the variation of energy ratio R_10/2(E₁₀/E₂) with R_4/2, for Ba–Dy and for Dy–Hf(N<104) and R_12/2. The role of the Z = 64 subshell and the N = 88–90 shape phase transition are illustrated in the Mallmann plot. The relative merits of the empirical formulae: rotation–vibration linearity model, the soft rotor formula and the power index formula are compared.

In this paper, the heavy cluster half-lives were calculated using the Wentzel–Kramers–Brillouin (WKB) method. First, we have considered the cluster and daughter nuclei as spherical and the half-lives have been obtained. Then, we have assumed two nuclei as deformed ones and calculations have been performed once again. Deformations of the emitted cluster and daughter nucleus have been presented in terms of elongation and neck thickness parameters. We investigated the influence of elongation and neck thickness parameters on cluster decay half-lives. Our results show that half-lives are affected by these parameters and obtained results for deformed nuclei are in better agreement with experimental data.