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Nuclear Theory·nucl-th

Wednesday·March 19, 2025

13 papers—6 primary·7 cross-listed

All13Primary6Cross-lists7
  1. 01

    Investigation of effects of pairing correlations on calculated -decay half-lives of fp-shell nuclei

    Asim Ullah · Jameel-Un Nabi · Muhammad Tahir

    Pairing of nucleons plays a key role in solving various nuclear physics problems. We investigate the probable effects of pairing correlations on the calculated Gamow-Teller (GT) strength distributions and the associated -decay half-lives. Computations are performed for a total of 35 fp-shell nuclei using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The nuclei were selected because of their importance in various astrophysical environments. Pairing gaps are one of the key parameters in the pn-QRPA model to compute GT transitions. We employed three different values of the pairing gaps obtained from three different empirical formulae in our calculation. The GT strength distributions changed significantly as the pairing gap values changed. This in turn resulted in contrasting centroid and total strength values of the calculated GT distributions and led to differences in calculated half-lives using the three schemes. The half-life values computed via the three-term pairing formula, based on separation energies of nucleons, were in best agreement with the measured data. We conclude that the traditional choice of pairing gap values, , may not lead to half-life values in good agreement with measured data. The findings of this study are interesting but warrant further investigation.

    nucl-thBraz.J.Phys.(2023)·3 citations
  2. 02

    Influence of the effective mass on the properties of nuclear matter at finite density and temperature

    Hajime Togashi🇰🇷 · Debashree Sen🇰🇷 · Hana Gil🇰🇷 · Chang Ho Hyun🇰🇷

    Significance of the chiral symmetry restoration is studied by considering the role of the modification of the nucleon mass in nuclear medium at finite density and temperature. Using the Korea-IBS-Daegu-SKKU density functional theory, we can create models that have an identical nuclear matter equation of state but different isoscalar and isovector effective masses at zero temperature. Effect of the effective mass becomes transparent at non-zero temperatures, and it becomes more important as temperature increases. Role of the effective mass is examined thoroughly by calculating the dependence of thermodynamic variables such as free energy, internal energy, entropy, pressure and chemical potential on density, temperature and proton fraction. We find that sensitivity to the isoscalar effective mass is several times larger than that of the isovector effective mass, so the uncertainties arising from the effective mass are dominated by the isoscalar effective mass. In the analysis of the relative uncertainty, we obtain that the maximum uncertainty is less than 2% for free energy, internal energy and chemical potential, but it amounts to 20% for pressure. Entropy shows a behavior completely different from the other four variables that the uncertainty is about 40% at the saturation density and increases monotonically as density increases. Effect of the uncertainty to properties of physical systems is investigated with the proto-neutron star. It is shown that temperature depends strongly on the effective mass at a given density and substantial swelling of the radius occurs due to the finite temperature. Equation of state is stiffer with smaller isoscalar effective mass, so the effect of the effective mass appears clearly in the mass-radius relation of the proto-neutron star, larger radius corresponding to smaller effective mass.

    nucl-thSymmetry(2025)·6 citations
  3. 03

    Electron capture and \b{eta}-decay rates for nuclei with A=65-80

    Asim Ullah · Jameel-Un Nabi

    Recently, a list of the top 50 most important electron capture (EC) and -decay (BD) nuclei, averaged throughout the stellar trajectory for , was published. The current study presents the calculation of EC and BD rates, from the published list with , on a detailed temperature-density grid. The EC and BD rates were calculated using the proton-neutron quasiparticle random phase approximation model (pn-QRPA). Our calculation did not employ the Brink-Axel hypothesis. A systematic comparison of the current calculation with previous pn-QRPA and independent particle model (IPM) results is presented for the first time. The reported EC rates are nearly the same when compared with the previous pn-QRPA calculation. On the other hand, the reported BD rates are generally smaller by up to an order of magnitude. Comparison with IPM results shows that our calculated rates are larger by two orders of magnitude. The current calculation may contribute to a more realistic simulation of the late phases of stellar evolution and the modeling of X-ray bursts.

    nucl-thPhys.Scripta(2022)·0 citations
  4. 04

    Delayed Thermal Relaxation of Rapidly Cooling Neutron Stars: Nucleon Superfluidity and Non-nucleon Particles

    Zhonghao Tu · Ang Li

    The thermal relaxation time of neutron stars, typically defined by a sudden drop in surface temperature, is usually on the order of 10 to 100 years. In this study, we investigate neutron star thermal relaxation by incorporating nucleon superfluidity and non-nucleonic particles, specifically considering hyperons as a representative case. We find that rapidly cooling neutron stars driven by neutron superfluidity and direct Urca processes demonstrate delayed thermal relaxation under specific physical conditions. The former acquires that the neutron critical temperature is small enough, whereas the latter depends on the presence of a small core that permits direct Urca processes. To explore these scenarios, we propose simple theoretical frameworks to describe these delayed thermal relaxation behaviors and discuss how an recently-established enhanced modified Urca rate influences the relaxation time. By confronting the theoretical results with the observation of Cassiopeia A, we can effectively constrain the maximum neutron critical temperature.

    nucl-thastro-ph.HEastro-ph.SRApJ·3 citations
  5. 05

    Investigation of -decay properties of neutron-rich Cerium isotopes

    Jameel-Un Nabi · Asim Ullah · Zeeshan Khan

    Reliable and precise knowledge of the -decay properties of neutron-rich nuclei is important for a better understanding of the -process. We report the computation of -decay properties of neutron-rich Cerium isotopes calculated within the proton-neutron quasiparticle random phase approximation (pn-QRPA) approach. A total of 34 isotopes of Ce in the mass range were considered in our calculation. Pairing gaps are recognized amongst the key parameters in the pn-QRPA model to compute Gamow-Teller (GT) transitions. We employed two different values of the pairing gaps obtained from two different empirical formulae in our computation. The GT strength distributions changed considerably with changes in the pairing gap values. This, in turn, resulted in contrasting centroid and total strength values of the GT distributions and led to differences in calculated half-lives using the two schemes. The traditional pairing gaps resulted in significant fragmentation of GT strength. However, the pairing gaps, calculated employing the formula based on separation energies of neutron and proton, led to computed half-lives in better agreement with the measured data.

    nucl-thPhys.Scripta(2022)·1 citation
  6. 06

    Nuclear configurational complexity in high-energy hadron-hadron scatterings

    G. Karapetyan🇧🇷

    This paper investigates high-energy hadron-hadron scattering utilizing AdS/QCD correspondence, gravitational form factors, and the Brower-Polchinski-Strassler-Tan pomeron exchange kernel. We use the configurational complexity to estimate the slope of the total cross section for hadron-hadron interactions at the high-energy regime. Our approach agrees well with the phenomenological cross sections regulated by Pomeron exchange involving the pion-nucleon, nucleon-nucleon, and pion-pion, in data from the TOTEM collaboration (LHC). In the case of pion-nucleon and pion-pion scattering, the agreement for the global critical point of the configurational complexity has good accuracy within 2.3\%.

    nucl-thhep-ph0 citations

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first authorsco-authorsvia INSPIRE