Nuclear Theory·nucl-th

Friday·March 1, 2024

15 papers—8 primary·7 cross-listed

01
Generator coordinate method with proton--neutron pairing fluctuations and magnetic properties of $N = Z$ odd--odd nuclei
K. Uzawa · N. Hinohara · T. Nakatsukasa
Pairing correlations play an important role in a variety of nuclear phenomena. However, a quantitative understanding of proton--neutron $(p n)$ pairing, especially isoscalar $p n$ pairing $(S = 1, T = 0)$ remains elusive. To clarify the property of $p n$ pairing, we investigate the roles of $p n$ pairing in the $M 1$ transition of $N = Z$ odd--odd nuclei. We develop a theoretical model based on the generator coordinate method (GCM) in which the isoscalar and isovector $p n$ -pair amplitudes are used as the generator coordinates. Using the particle and the angular-momentum projections, the $p n$ -pair GCM well reproduces the $M 1$ transition of odd--odd nuclei for the exactly solvable SO(8) model. We apply the method to $N = Z$ odd--odd nuclei and find that the experimental values of $B (M 1)$ are well reproduced. We also study the sensitivity of $B (M 1)$ to the strength of the isoscalar pairing interaction.
nucl-thPTEP(2024)·6 citations
02
Observational Probes of the Neutron Star Equation of State with Hyperons, Bosonic Dark Matter, and Quark Matter
Mahboubeh Shahrbaf🇵🇱 · Davood Rafiei Karkevandi🇵🇱 · Alexander Ayriyan🇵🇱 · Stefan Typel🇩🇪
Context. The presence of dark matter in neutron stars is of growing interest due to its potential impact on the structure and observable properties of these objects. Among the various candidates, the hypothetical sexaquark has emerged as a promising bosonic dark matter particle, potentially forming under extreme conditions in neutron star cores. Aims. We investigate whether a hybrid neutron star model that includes hyperons, bosonic dark matter (in the form of sexaquarks), and deconfined quark matter can satisfy all current observational constraints. We particularly focus on identifying the range of sexaquark masses consistent with mass-radius measurements and the tidal deformability limit. Methods. We used the DD2Y-T model for the hadronic phase, which includes hyperons, and a nonlocal Nambu-Jona-Lasinio model for the deconfined quark phase. The phase transition was modeled as a smooth crossover using the replacement interpolation construction method. Sexaquark-baryon interactions were introduced via an effective mass shift representing repulsion. We incorporated the full set of current observational data, including NICER measurements of PSRs J0437-4715 and newly published J0614-3329 data, and performed a Bayesian analysis to constrain the sexaquark mass. Results. Our results show that the presence of the sexaquark softens the equation of state, enabling the hybrid model to satisfy both the radius and tidal deformability constraints around the canonical 1.4 M_\odot neutron stars. We find that hybrid EOSs with a sexaquark mass around 1900 MeV are in agreement with all available constraints, including those from HESS J1731-347 and PSR J0952-0607, which represent the lowest and highest mass neutron stars observed to date. The Bayesian analysis favors a sexaquark mass range of 1885-1935 MeV, supporting the potential relevance of this exotic particle in neutron star interiors.
nucl-thhep-phAstron.Astrophys.(2026)·17 citations
03
Spectroscopy of N=50 isotones with the valence-space density matrix renormalization group
A. Tichai · K. Kapás · T. Miyagi · M. A. Werner · Ö. Legeza · A. Schwenk · G. Zarand
The recently proposed combination of the valence-space in-medium similarity renormalization group (VS-IMSRG) with the density matrix renormalization group (DMRG) offers a scalable and flexible many-body approach for strongly correlated open-shell nuclei. We use the VS-DMRG to investigate the low-lying spectroscopy of N=50 isotones, which are characteristic for their transition between single-particle and collective excitations. We also study electromagnetic transitions and show the advantage of the VS-DMRG to capture the underlying physics more efficiently, with significantly improved convergence compared to state-of-the-art shell-model truncations. Combined with an analysis of quantum information measures, this further establishes the VS-DMRG as a valuable method for ab initio calculations of nuclei.
nucl-thcond-mat.str-elPLB(2024)·24 citations
04
A direct probe of $Λ$ potential in nuclear medium
Gao-Chan Yong🇨🇳
Using the Liège intranuclear-cascade model together with the ablation model ABLA, an investigation is conducted into the effects of $Λ$ potential in $Λ$ -nucleus and $Λ$ -hypernucleus-nucleus collisions across various beam energies. The findings show that the angle and transverse-momentum distributions of scattered $Λ$ hyperon, the scattering cross section of the $Λ$ hyperon in $Λ$ -nucleus collisions as well as the rapidity distribution of $Λ$ hyperon in $Λ$ -hypernucleus-nucleus collisions are significantly influenced by the strength of the $Λ$ potential in these scattering reactions across various beam energies. These demonstrations, unhindered by the uncertainties of $Λ$ and hypernuclei productions in nuclear medium, allow for a direct investigation of the $Λ$ potential, especially its momentum dependence. The criticality of probing the $Λ$ potential is closely associated with the resolution of the "hyperon puzzle" in neutron stars.
nucl-thhep-exhep-phnucl-exPLB(2024)·4 citations
05
Hadron-quark phase transition in the neutron star with vector MIT bag model and Korea-IBS-Daegu-SKKU functional
Debashree Sen🇰🇷 · Hana Gil🇰🇷 · Chang Ho Hyun🇰🇷
Employing the Korea-IBS-Daegu-SKKU (KIDS) density functional for the hadron phase and the MIT bag model with vector (vBag) model for the quark phase, we obtain hadron-quark phase transition in neutron stars considering Maxwell construction. The structural properties of the resultant hybrid stars are computed for three different values of bag constant ( $B$ ) in the range $B^{1/4} =$ (145 $-$ 160 MeV). We study the effects of symmetry energy ( $J$ ) on the hybrid star properties with the different KIDS model and found that $J$ has important influence not only on the transition properties like the transition mass, transition radius and jump in density due to phase transition, but also on the stability of the hybrid stars. The vector repulsion of the quark phase via the parameter $G_{V}$ has profound influence in obtaining reasonable hybrid star configurations, consistent with the recent astrophysical constraints on the structural properties of compact stars. Within the aforesaid range of $B$ , the value of $G_{V}$ is constrained to be 0.3 $≲ G_{V} ≲$ 0.4 in order to obtain reasonable hybrid star configurations.
nucl-thhep-phFront.Astron.Space Sci.(2024)·6 citations
06
Investigation of the determination of nuclear deformation using high-energy heavy-ion scattering
Shin Watanabe · Takenori Furumoto · Wataru Horiuchi · Tadahiro Suhara · Yasutaka Taniguchi
Background: Nuclear deformation provides a crucial characteristic of nuclear structure. Conventionally, the quadrupole deformation length of a nucleus, $δ_{2}$ , has often been determined based on a macroscopic model through a deformed nuclear potential with the deformation length $δ_{2}^{(pot)}$ , which is determined to reproduce the nuclear scattering data. This approach assumes $δ_{2} = δ_{2}^{(pot)}$ although there is no theoretical foundation. Purpose: We clarify the relationship between $δ_{2}$ and $δ_{2}^{(pot)}$ for high-energy heavy-ion scattering systematically to evaluate the validity of the conventional approach to determine the nuclear deformation. Method: The deformation lengths for the $^{12}$ C inelastic scattering by $^{12}$ C, $^{16}$ O, $^{40}$ Ca, and $^{208}$ Pb targets at $E / A$ = 50--400 MeV are examined. First, we perform microscopic coupled-channel (CC) calculations to relate $δ_{2}$ of the deformed density into the inelastic scattering cross section. Second, we use the deformed potential model to determine $δ_{2}^{(pot)}$ so as to reproduce the microscopic CC result. We then compare $δ_{2}^{(pot)}$ with $δ_{2}$ . Results: We find that $δ_{2}^{(pot)}$ is about 20--40 \% smaller than presumed $δ_{2}$ , showing strong energy and target dependence. Further analysis, which considers higher-order deformation effects beyond the derivative model, reveals that $δ_{2}^{(pot)}$ is still about 15--35 \% smaller than $δ_{2}$ . Conclusion: Our results suggest that one needs to be careful when the deformed potential model for the high-energy heavy-ion scattering is used to extract the nuclear deformation. The conventional approach may underestimate the deformation length $δ_{2}$ systematically.
nucl-thPRC(2024)·0 citations
07
Symmetry Energy from Two-Nucleon Separation Energies of Pb and Ca Isotopes
Myeong-Hwan Mun · Eunja Ha · H. Sagawa · Gianluca Colò · Myung-Ki Cheoun
We investigate the symmetry energy in relation with the two-proton and two-neutron separation energies using different nuclear mass data. For this aim, we exploit the deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc), FRDM2012 and AME2020 data. First, we study the two-proton and two-neutron separation energies in Pb and Ca isotopes by subtracting the contribution of Coulomb energy. They show a strong correlation with neutron number as well as with the neutron skin thickness. By taking the relative difference of both separation energies, we derive the symmetry energy from Ca and Pb isotopes. Since the nuclear surface contributes to the symmetry energy, we deduce the volume symmetry energy by subtracting the surface contribution using several mass models. The obtained symmetry energy coefficient, $a_{sy m}$ , is 20.0 $\sim$ 22.7 MeV for Pb isotopes and 18.7 $\sim$ 19.3 MeV for Ca isotopes from the DRHBc mass table data, while the results from other mass tables are 19.6 $\sim$ 22.1 (20.7 $\sim$ 22.3) MeV for Pb isotopes and 18.9 $\sim$ 19.0 (19.6 $\sim$ 19.7) MeV for Ca isotopes from AME2020 (FRDM2012) data. The volume contribution to the asymmetry coefficient, $a_{sy m}^{v}$ , which depends on the ratio of the surface to the volume energy coefficients, $a_{s} / a_{v}$ , is also provided for each mass model. Since the ratio $a_{s} / a_{v}$ is neither determined by nuclear theory, nor by experimental data, we have investigated $a_{sy m}^{v}$ by using the ratio $a_{s} / a_{v}$ as a free parameter, and have obtained $a_{sy m}^{v} =$ 27.0 MeV, almost irrespective of nuclear model and isotopic chain, with the ratio $a_{s} / a_{v}$ constrained as $a_{s} / a_{v} = 1.10 \sim 1.13$ .
nucl-thPRC(2024)·9 citations
08
Infinite Order Hydrodynamics: An Analytical Example
Lorenzo Gavassino🇺🇸
We construct a kinetic model for matter-radiation interactions whose hydrodynamic gradient expansion can be computed analytically up to infinite order in derivatives, in the fully nonlinear regime, and for arbitrary flows. The frequency dependence of the opacity of matter is chosen to mimic the relaxation time of a self-interacting scalar field. In this way, the transient sector simulates that of a realistic quantum field theory. The gradient series is found to diverge for most flows, in agreement with previous findings. We identify, for the model at hand, the mechanism at the origin of the divergence, and we provide a successful regularization scheme. Additionally, we propose a universal qualitative framework for predicting the breakdown of the gradient expansion of an arbitrary microscopic system undergoing a given flow. This framework correctly recovers all previously known instances of gradient expansion divergence. As a new prediction, we show that the gradient expansion diverges when the energy-dependent mean free path is unbounded above.
nucl-thastro-ph.HEgr-qchep-ph+1PRL(2024)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE