International Journal of Modern Physics E

At very high densities, electrons react with protons to form neutron-rich matter. This material is central to many fundamental questions in nuclear physics and astrophysics. Moreover, neutron-rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in ²⁰⁸Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron-rich matter. Gravitational waves (GW) open a new window on neutron-rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, neutrinos from core collapse supernovae (SN) provide another, qualitatively different probe of neutron-rich matter. Neutrinos escape from the surface of last scattering known as the neutrino-sphere. This is a low density warm gas of neutron-rich matter. Neutrino-sphere conditions can be simulated in the laboratory with heavy ion collisions. Observations of neutrinos can probe nucleosyntheses in SN. Simulations of SN depend on the equation of state (EOS) of neutron-rich matter. We discuss a new EOS based on virial and relativistic mean field calculations. We believe that combing astronomical observations using photons, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and radioactive beams will fundamentally advance our knowledge of compact objects in the heavens, the dense phases of QCD, the origin of the elements, and of neutron-rich matter.

Alpha clustering in nuclei at present is a well studied and reasonably well accepted property of the nucleus. Less well appreciated and more ambiguous is the role of A = 3 clustering, i.e. helion and triton, in nuclei. Here we try to place A = 3 clustering in nuclei into its proper perspective, first by pointing out strong experimental evidences which indicate its clear presence in nuclei and second showing as to how to include these A = 3 clusters in a proper and consistent theoretical understanding of the nuclear phenomenon.

Excitation functions for the reactions ⁸⁹ Y(p, n)^89gZr and ⁸⁹Y(p, n)^89mZr have been measured over the energy ranges from threshold to 15 MeV using stacked foil activation technique. The isomeric cross-section ratio σ_m/(σ_m+σ_g) for the formation of ^{89m, g}Zr was determined. The excitation functions and isomeric cross-section ratios were calculated for the reactions ⁸⁹Y(p, γ)^{90m, g}Zr, ⁸⁹ Y(p, n)^{89m, g}Zr, ⁸⁹Y(p, p)^{89m, g}Y and ⁸⁹Y(p, αn)^{85m, g}Sr also for energy range 4–40 MeV. The PE emission fraction is found to depend strongly on the energy of the incident particle. The isomeric cross-section ratio is found to depend strongly on the relative spins of the isomeric and ground state and some dependence on energy difference between the levels.

In this paper, pre-equilibrium-emission has been investigated using particle-γ coincidence technique. Forward-to-backward yield ratios of different reaction products have been measured in ¹⁶O+¹⁶⁹Tm system at 5.6 MeV/nucleon. Coincidences between prompt-γ-rays and charged particles emitted in various angular zones have been recorded to identify different reaction products. Several gating conditions have been projected onto the energy spectra to achieve the information about mode of reaction. Yield profiles of fusion/fusion-like channels identified from forward/backward/sideways particle (Z = 1, 2)-gated-spectra have been measured. High yield in forward cone has been observed from the experimentally measured forward-to-backward yield ratios. The enhanced forward cone yield has been attributed to the pre-equilibrium-emission. The maximum observed spin is found to be decreased with the number of proton emitted from the composite nucleus during the equilibrium and/or pre-equilibrium decay.

We investigate tensor effects in pygmy dipole excitations for the case of neutron-rich nuclei ⁶⁸Ni and ¹²⁴Sn using effective nucleon–nucleon Skyrme interaction. We use the Hartree–Fock–Bogoliubov (HFB) theory and employ the quasiparticle random phase approximation (QRPA). We calculate and compare the PDR and also GDR strength in the PDR–GDR energy region for QRPA calculations with and without tensor correlations. The most obvious results for the dipole excitations calculations are strongly dependent on the tensor terms. We see that the tensor correlations are more active at around 14–20 MeV, especially for the neutron-rich nuclei ⁶⁸Ni. We also compare the PDR calculations with their experimental results for the different proton–neutron tensor coupling constants.

The relativistic four-quark equations are found in the framework of coupled-channel formalism. The dynamical mixing of the meson–meson states with the four-quark states is considered. The four-quark amplitudes of the negative parity tetraquarks including the quarks of three flavors (u, d, s) and the charmed quark are constructed. The poles of these amplitudes determine the masses of tetraquarks. The mass values of low-lying tetraquarks with the spin-parity J^P = 0^-, 1^-, 2^-, 3^- are calculated.

In this work, the logarithmic half-life [log₁₀(T_1/2)] values have been reported for the exotic decay of some neutron rich even–even parent nuclei (56≤Z≤64) accompanied by the emission of alpha-like and non-alpha-like clusters in the trans-tin region. These values were calculated by using the single line of universal curve (UNIV) for alpha and cluster radioactive decay as well as the universal decay law (UDL). The half-life values were also separately calculated by considering the interacting nuclear potential barrier as the sum of Coulomb and proximity potentials. The half-life values based on the three calculations mentioned above, were found to agree with one another within a few orders of magnitude. Possible conclusions are drawn based on the present study.

We revisit the negative energy solutions of the Dirac (and Klein–Gordon) equation, which become relevant at very high energies in the context of the Feshbach–Villars formulation, and study several symmetries which follow therefrom. Significant consequences are briefly examined.

Three subjects are considered here: the relativistic hydrodynamics equations for a boost-invariant expanding fluid; the fuzzy bag model for the pressure which recently appeared in (QCD) phenomenology; and the early space-time evolution of the QCD matter, drawn from model studies, which can also be expected to arise in realistic fluid dynamics relevant to heavy ion collisions at LHC.

We show here that the Hugenholtz–Van Hove theorem for an infinite Fermi system remains valid even with all possible multi-body interaction terms taken into account either separately or in any combination under Hartree–Fock approximation. We further extend the theorem to obtain its most generalized form that would hold good for any multi-component Fermi system.

The ambiguities proposed by Benhar et al., about the the different implementation of the impulse approximation for calculating the response function of many-fermion systems, are investigated theoretically in the frame work of simple harmonic oscillator shell model for the double closed shell nuclei, e.g. ⁴He, ¹⁶O and ⁴⁰Ca nuclei. For each nucleus as a finite system, we evaluate the response function by using its definition in terms of the one-body spectral function and the one-body momentum distribution. It is demonstrated analytically, that there exists a sizable shift between the two schemes for each nucleus, which increases as we switch to the heavier nuclei. So one can conclude that for the nuclei with atomic number less than 4, such as ²H, ³H or ³He, it is good approximation to ignore this discrepancy. This conclusion is important for theoretical explanation of the ongoing deep inelastic scattering (DIS) experiments of ³H or ³H in the Jefferson Laboratory. However present calculation confirms the work of Modarres and Younesizadeh (2010), in which they have shown that, the above shift can be removed by imposing the impulse approximation in the same footing in the many-fermion wave-function.

We study the binding energy, root-mean-square radius and quadrupole deformation parameter for the synthesized superheavy element Z = 115, within the formalism of relativistic mean field theory. The calculation is dones for various isotopes of Z = 115 element, starting from A = 272 to A = 292. A systematic comparison between the binding energies and experimental data is made.The calculated binding energies are in good agreement with experimental result. The results show the prolate deformation for the ground state of these nuclei. The most stable isotope is found to be ²⁸²115 nucleus (N = 167) in the isotopic chain. We have also studied Q_α and T_α for the α-decay chains of ^{287, 288}115.

The γ-unstable limit of the interacting boson model for identical nucleon systems (IBM-I) was studied within the framework of the SD-pair shell model. The results show that the properties of this limit as realized within the boson picture can be reproduced well within a fermion framework.