Nuclear Theory·nucl-th

Tuesday·July 23, 2024

10 papers—7 primary·3 cross-listed

01
[Submitted on 19 Jul 2024]
Superfluid fraction in the rod phase of the inner crust of neutron stars
Giorgio Almirante🇫🇷 · Michael Urban🇫🇷
The rod phase as it is expected in the bottom layers of neutron-star crusts is analyzed within the Hartree-Fock-Bogoliubov framework. In order to well describe the interplay between band structure and superfluidity, periodicity of the lattice is taken into account using Bloch boundary conditions. A relative flow between the rods and the surrounding neutron gas is introduced in a time-independent way. This induces a non-trivial phase of the complex order parameter, leading to a counterflow between neutrons inside and outside the rods. With the resulting current, we compute the actual neutron superfluid fraction. For the latter our results are significantly larger than previous ones obtained in normal band theory, indicating that the normal band theory overestimates the entrainment effect.
Comments:
11 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2407.14574 [pdf]
PRC(2024)·10 citations
02
[Submitted on 19 Jul 2024]
Restricted Boltzmann Machines Propagators for Auxiliary Field Diffusion Monte Carlo
Jordan M. R. Fox · Alessandro Lovato · Alessandro Roggero · Ermal Rrapaj
The auxiliary field diffusion Monte Carlo method uses imaginary-time projection techniques to accurately solve the ground-state wave function of atomic nuclei and infinite nuclear matter. In this work, we present a novel representation of the imaginary-time propagator based on restricted Boltzmann machines. We test its accuracy against the routinely employed Hubbard-Stratonovich transformations by evaluating ground-state energies and single-particle densities of selected light nuclei. This analysis paves the way for incorporating more realistic nuclear potentials in the auxiliary field diffusion Monte Carlo method, including isospin-dependent spin-orbit terms and cubic spin-isospin operators, which characterize accurate phenomenological and chiral effective field theory Hamiltonians.
Comments:
8 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2407.14632 [pdf]
0 citations
03
[Submitted on 21 Jul 2024]
Shape coexistence in Ne isotopes and hyperon impurity effect on low-lying states
Huai-Tong Xue🇨🇳 · Ji-Wei Cui🇨🇳 · Q. B.Chen🇨🇳 · Xian-Rong Zhou🇨🇳 · Hiroyuki Sagawa🇯🇵
Based on the beyond-mean-field Skyrme-Hartree-Fock model, we investigate the shape coexistence in Ne isotopes and the effect of $\la$ hyperon on the energy level structure in the nuclei. The up-to-date Skyrme-type $N \la$ interaction SLL4 and the $N N$ interaction SGII are employed. Low-lying energy spectra of $^{20, 22, 24, 26, 28, 30, 32, 34}$ Ne, including the low-lying states with $J \leq 6$ , are predicted, discussed in detail, and found in good agreement with experimental results. The electric quadrupole transition rate is also examined. The coexistences of a ground state rotational band and a $\be$ vibrational band are revealed in $^{20, 22, 24}$ Ne. Unlike the previously discovered shrinkage effect of $\la_{s}$ on the ground state nuclei, it is found that the $\la_{s}$ may alter the excitation mode of the second band by affecting the distribution of the collective wave function, thereby causing the $\be$ vibrational band transitions to a vibrational band with equidistant energy levels.
Comments:
12 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2407.15048 [pdf]
PRC(2024)·4 citations
04
[Submitted on 21 Jul 2024]
Anisotropic flow fluctuation as a possible signature of clustered nuclear geometry in O-O collisions at the Large Hadron Collider
Suraj Prasad🇮🇳 · Neelkamal Mallick🇮🇳 · Raghunath Sahoo🇮🇳 · Gergely Gábor Barnaföldi🇭🇺
Nuclei having $4 n$ number of nucleons are theorized to possess clusters of $α$ particles ( $^{4}$ He nucleus). The Oxygen nucleus ( $^{16}$ O) is a doubly magic nucleus, where the presence of an $α$ -clustered nuclear structure grants additional nuclear stability. In this study, we exploit the anisotropic flow coefficients to discern the effects of an $α$ -clustered nuclear geometry with respect to a Woods-Saxon nuclear distribution in O--O collisions at $s_{NN} = 7$ TeV using a hybrid of IP-Glasma + MUSIC + iSS + UrQMD models. In addition, we use the multi-particle cumulants method to measure anisotropic flow coefficients, such as elliptic flow ( $v_{2}$ ) and triangular flow ( $v_{3}$ ), as a function of multiplicity class. Anisotropic flow fluctuations, which are expected to be larger in small collision systems, are also studied for the first time in O--O collisions. It is found that an $α$ -clustered nuclear distribution gives rise to an enhanced value of $v_{2}$ and $v_{3}$ for the low-multiplicity events. Consequently, a rise in $v_{3} / v_{2}$ is also observed for the 0--10\% multiplicity class. Further, for $α$ -clustered O--O collisions, fluctuations of $v_{2}$ are larger for the highest multiplicity events, which decrease as the final-state multiplicity decreases. In contrast, for a Woods-Saxon $^{16}$ O nucleus, $v_{2}$ fluctuations show an opposite behavior with decreasing multiplicity. When confronted with experimental data, this study may reveal the importance of the nuclear density profile on the discussed observables and provide physics validation for the hybrid model discussed in this work.
Comments:
15 pages and 12 captioned figures, Same as the published version in Phys. Letts. B
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2407.15065 [pdf]
PLB(2025)·22 citations
05
[Submitted on 21 Jul 2024]
The Relative Abundance of Correlated Spin-zero Nucleon Pairs
Raz Yankovich · Ehoud Pazy · Nir Barnea
We utilize the generalized contact formalism in conjunction with the Woods-Saxon mean-field description of the long-range part of the nuclear wave function to assess the relative prevalence of short-range correlation pairs within atomic nuclei. We validate our approach by fitting experimental charge density results and electron scattering experiments to a very good agreement. Applying our model, we calculate the spin-zero short-range correlations contact ratios. Interestingly, for nuclei with $A > 50$ , we observe a notable dependence on the neutron-to-proton ratio $N / Z$ . Specifically, the probability per nucleon to find neutron-neutron pairs increases, while that of proton-proton pairs decreases, whereas the probability of finding neutron-proton pairs remains relatively constant. To interpret this isospin symmetry breaking effect, we employ a simple model based on generalized Levinger constants, linking it to differences in nuclear proton and neutron radii.
Comments:
5 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2407.15068 [pdf]
PRC(2025)·4 citations
06
[Submitted on 21 Jul 2024]
Reaction of deuteron with a heavy nucleus at low energies
Pankaj Jain · Harishyam Kumar · K. Ramkumar
We extend the recently proposed mechanism for inducing low energy nuclear reactions (LENR) to compute the reaction rate of deuteron with a heavy nucleus. The process gets dominant contribution at second order in the time dependent perturbation theory and is assisted by a resonance. The reaction proceeds by breakdown of deuteron into a proton and a neutron due to the action of the first perturbation. In the second, nuclear perturbation, the neutron gets captured by the heavy nucleus. Both perturbations are assumed to be electromagnetic and lead to the emission of two photons, one at each vertex. The heavy nucleus is taken to be $^{58}$ Ni although many other may be considered.The reaction rate is found to be very small unless assisted by some special conditions. In the present case we assume the presence of a nuclear resonant state. In the presence of such a state we find that the reaction rate is sufficiently large to be observable in laboratory even at low energies.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2407.15137 [pdf]
2 citations
07
[Submitted on 22 Jul 2024]
Average speed of sound in neutron stars
Michał Marczenko
The structure of the dense-matter equation of state is essential for the phenomenology of neutron stars. In this work, I relate the thermodynamic properties to the average speed of sound in the interior of a star. I study the consequences of the vanishing of the trace anomaly. In particular, I show that if the trace anomaly vanishes in the centers of maximally massive neutron stars, the speed of sound likely exceeds its conformal value and exhibits nonmonotonic behavior. I also find that the additional assumption of positive definiteness of the trace anomaly naturally induces a local peak of the speed of sound at densities realized in the cores of neutron stars. I also reanalyze the stability condition for hybrid neutron stars. Possible implications for the dense matter equation of state and the phenomenology of neutron stars are also discussed.
Comments:
matches published version
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2407.15486 [pdf]
PRC(2024)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE

Superfluid fraction in the rod phase of the inner crust of neutron stars

Restricted Boltzmann Machines Propagators for Auxiliary Field Diffusion Monte Carlo

Shape coexistence in Ne isotopes and hyperon impurity effect on low-lying states

Anisotropic flow fluctuation as a possible signature of clustered nuclear geometry in O-O collisions at the Large Hadron Collider

The Relative Abundance of Correlated Spin-zero Nucleon Pairs

Reaction of deuteron with a heavy nucleus at low energies

Average speed of sound in neutron stars

Affiliations