International Journal of Modern Physics E

In this paper, we review the most common descriptions for the first-order phase transition to deconfined quark matter in the core of neutron stars. We also present a new description of these phase transitions in the core of proto-neutron stars, in which more constraints are enforced so as to include trapped neutrinos. Finally, we calculate the emission of gravitational waves associated with deconfinement phase transitions, discuss the possibility of their detection, and how this would provide information about the equation of state of dense matter.

In previous works, we examined the systematics of magnetic dipole transitions in a single j shell. We here extend the study to large space calculations. We consider the nuclei ${}^{44}$Ti, ${}^{46}$Ti and ${}^{48}$Cr. Of particular interest are the contributions to $B(M1)$ of the spin and orbital parts of the magnetic dipole operator. Whereas usual scissors mode analyses have as an initial state the $J=0^{+}$ ground state (of an even-even nucleus), we here start with the lowest $J=1^{+},T=1$ state. This enables us to reach many more states, e.g., $J=2,T=0,$ 1, and 2 and thus get a better picture of the collectivity of this state.

The intrinsic reaction mechanism of proton-induced composite particle pre-equilibrium emission is well known to be a statistical multistep process. However, until recently it was still not clear how important the competition between pickup and knockout is to produce a composite ejectile in the multistep sequence. An evaluation of recent ($p,\alpha$) results at incident energies from 65 to 160MeV and on representative target nuclei is presented. The virtue of analyzing power angular distributions to unravel the details of the reaction mechanism is discussed and future possible avenues of investigation are explored.

The collision centrality dependencies of the average kinematical characteristics of the negative and positive pions, produced in ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions at $4.2A\mathrm{\text{GeV}}/c$, were investigated. The ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ proved to be $1.20\pm 0.05$, $1.08\pm 0.04$ and $1.04\pm 0.03$ in the peripheral, semicentral, and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collision events, respectively, decreasing noticeably with increasing collision centrality. The suppression (decrease) of the ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ was observed in the semicentral and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions as compared to the ratio $(\approx 1.22)$, estimated using the simple model for ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collision system. The ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ estimated using the simple model agreed well with the corresponding ratio $(\approx 1.24)$, estimated for ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions at $4.2A\mathrm{\text{GeV}}/c$ based on the Wounded Nucleon Model (WNM). Comparison of the emission angle as well as momentum distributions of the charged pions in the peripheral and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions revealed the significant decrease of the fraction of the relatively fast charged pions (with smaller emission angles) and increase of the fraction of the relatively slow charged pions (with larger emission angles) with an increase in collision centrality. The results of the present analysis can be useful for analysis of the centrality dependence of the charged pion production in heavy ion collisions at high energies.

The evolution of close binary stars in mass asymmetry (transfer) coordinate is considered. The conditions for the formation of stable symmetric binary stars are analyzed. The role of symmetrization of asymmetric binary star in the transformation of potential energy into internal energy of star and the release of a large amount of energy is revealed.

The elastic and inelastic scatterings of $\alpha$-particles were investigated at an energy of 40MeV with excitation of low-lying states of the ${}^{11}$B nucleus [0.0 (3/2${}^{-}$), 4.445 (5/2${}^{-}$), 6.74 (7/2${}^{-}$), 2.125 (1/2${}^{-}$) and 5.02MeV (3/2${}^{-}$)]. The analysis of the experimental angular distributions was carried out via the coupled channels method within the framework of the collective model. The value of the quadrupole deformation parameter ${\beta }_2=0.545$ was extracted. Calculations indicate a preference for a negative sign for deformation. It is shown that the exchange mechanism with the transfer of the heavy ⁷Li cluster does not play an important role in the scattering of $\alpha$-particles on ${}^{11}$B nuclei at an energy of 40MeV.

For the measurement of two-pion Bose–Einstein correlations (BEC) in reactions with $\pi \pi \mathrm{\text{x}}$ final state particles, a new event-mixing technique is proposed. The new technique introduces a new mixing constraint, namely energy hierarchy correspondence (EHC) cut, which requires that two bosons being swapped should be equal in energy hierarchy in their original events. Numerical tests are performed to check the validity of the new mixing method. Compared to the previous proposed mixing technique (He et al., Chin. Phys. C 42 (2018) 074004), this new method has smaller systematic uncertainties, improving the accuracy of fit BEC parameters.

The effects of thermal fluctuations on pairing properties of nuclei with inclusion of angular momentum have been investigated. To treat nuclei at finite temperature and angular momentum, we have extended the formalism in which the mean value of the gap parameter is used to obtain thermal properties of nuclei based on the BCS scheme [Z. Kargar and V. Dehghani, J. Phys. G, Nucl. Part. Phys. 40 (2013) 045108] let us name it MEGBCS. The results obtained for ${}^{94}\mathrm{\text{Mo}}$ nucleus show the appearance of thermally assisted pairing correlations with increasing angular momentum. Also, the $S$-shaped heat capacity found experimentally [K. Kaneko et al., Phys. Rev. C 74 (2006) 024325] and theoretically, interpreted as the second phase transition in mesoscopic systems, disappears with increasing angular momentum above a critical value. The nuclear level density of ${}^{94}\mathrm{\text{Mo}}$ is calculated versus excitation energy at various values of total angular momentum. The total level density matches the experimental data closely.

Models of neutron stars (NSs) with hyperon cores are constructed with an effective chiral model in mean-field approximation. The hyperon couplings are fixed by reproducing their experimentally determined binding energies. The impact of these couplings on population of different particles and the equation of state (EoS) are studied in this work. The global properties of NSs like gravitational mass, radius, baryonic mass and central density are calculated using parametrized Tolman–Oppenheimer–Volkoff equations (PTOVs) with special emphasis on two effects of pressure — one contributing to total mass density and the other to self-gravity of the star. We find that with PTOV solutions in static conditions, a softer EoS (including hyperons) can also lead to massive stellar configurations of NSs, which are in good agreement with the observed maximum mass bound of $\approx 2M_{\odot }$ (PSR J0348-0432). Estimates of $R_{1.4}$ and $R_{1.6}$, obtained with the PTOV equations, are consistent with the recent findings of the same from the data analysis of gravitational waves (GW170817) observation.

The feasibility of alpha and cluster decay from Pt isotopes has been investigated within the framework of Skyrme Hartree–Fock–Bogoliubov (HFB) theory. Calculations have been carried out for various Skyrme forces. Harmonic oscillator and transformed harmonic oscillator basis are used to solve HFB equations. The role played by shell closure is analyzed. Half-lives are estimated with the help of Universal Decay Law (UDL). Geiger–Nuttal plots are also drawn and their linear nature is successfully reproduced.

Based on the obtained ${}^7\mathrm{\text{Li}}$ global optical model potential, the global phenomenological optical model potential for ${}^{11}\mathrm{\text{B}}$ projectile is obtained by fitting the experimental data of ${}^{11}\mathrm{\text{B}}$ elastic scattering angular distributions from ${}^{28}\mathrm{\text{Si}}$ to ${}^{209}\mathrm{\text{Bi}}$ targets with incident energies below 100MeV. Using the found global optical model potential, the reaction cross-sections are predicted and compared with the available experimental data. Moreover, the elastic-scattering angular distributions and reaction cross-sections for isotopic chain ${}^{8,10}\mathrm{\text{B}}$ projectiles are predicted by the ${}^7\mathrm{\text{Li}}$ global optical model potential at different incident energies. These results are also compared with the corresponding experimental data. The performance shows that the ${}^{8,10,11}\mathrm{\text{B}}$ global phenomenological optical model potentials can give a satisfactory description for elastic scattering of these projectiles.

The nuclei in the $A=130,$ $100$ and $80$ regions, lying on both sides of the $\beta$-stability line, continue to be of interest for their complex nuclear structures. The Grodzins product rule (GPR) viz. $[E(2_1^{+})\times B(E2,0_1^{+}\to 2_1^{+})=\mathrm{\text{constant}}\times Z^2{A}^{-2/3}]$, for the ground bands of even-$Z$ even-$N$ nuclei provides a useful approach to study these structures. The utility of our method, displaying the linear relation of $B(E2)$ to $[1/E(2_1^{+})]$, is illustrated for the $Z=30$ Zn to $Z=48$ Cd series of isotopes. The spread of the data on the linear plots enables a quick view of the shape phase transitions. The role of the shells and the subshells, at spherical and deformed shell gaps for neutrons and protons, with their mutual re-inforcement and the shape phase transition are vividly visible on our plots. The development of collectivity in this region is also linked to the effective number of valence nucleons above the magic number of $Z=20$, and 28 rather than $Z=40$, for Mo to Cd isotopes for a microscopic calculation.

Charged hadron production in the $e^{+}{e}^{-}$ annihilations at 91 to 206GeV in full phase space and in $\overline{p}p$ collisions at 200 to 900GeV collision energies are studied using nonextensive Tsallis and stochastic Weibull probability distributions. The Tsallis distribution shows better description of the data than the Weibull distribution. The 2-jet modification of the statistical distribution is applied to describe $e^{+}{e}^{-}$ data. The main features of these distributions can be described by a two-component model with soft, collective interactions at low transverse energy and hard, constituent interactions dominating at high transverse energy. This modification is found to give much better description than a full-sample fit, and again Tsallis function is found to better describe the data than the Weibull one pointing at the nonextensive character of the multiparticle production process.