Nuclear Theory·nucl-th

Friday·December 19, 2025

20 papers—9 primary·11 cross-listed

01
Two-proton emission as source of spin-entangled proton pairs
Tomohiro Oishi🇯🇵 · Masaaki Kimura🇯🇵
We show that a two-proton emitter with a diproton-correlated initial state can act as a source of spin-correlated proton pairs. Using a time-dependent three-body model, we investigate the two-proton emission of $^{16}$ Ne ( $^{14}$ O $+ 2 p$ ) and analyze the spin correlation of the emitted protons. We find that, when the emission proceeds as a democratic three-body process from an initial state containing a spin-singlet diproton correlation, the emitted protons exhibit a pronounced spin-correlation pattern exceeding the local-hidden-variable bound. This spin correlation closely resembles that of a pure spin-singlet pair. In contrast, this pattern is lost when the process is dominated by the sequential emission or when the initial diproton correlation is absent. These results demonstrate that a certain class of two-proton emitters can deliver spin-entangled proton pairs, and their spin correlation reflects the diproton correlation embedded in the initial state.
nucl-thnucl-exquant-phPLB(2026)·1 citation
02
Role of tensor forces in nuclei
Yu.P.Lyakhno
Recently, calculations of the ground states of the lightest nuclei have been performed using highly accurate data on realistic internucleon forces. In this paper, these results were used to describe the properties of nuclei with nucleon numbers $A > 4$ . Taking into account tensor forces leads to the conclusion that the four subsystems in the nucleus with zero nucleon orbital momenta are combined predominantly into the $^{1} S_{0}$ cluster. Subsystems with nonzero orbital momenta also combine into clusters with lower potential energy. This approach allows us to consistently explain the lifetime of the $^{8}$ Be nucleus, the Hoyle state, the sequential mechanism of the reaction with the emission of $α$ particles, the shift of the reaction threshold, and more. The assumption of the existence of a one-dimensional effective interaction of nucleons in the nucleus leads to the conclusion that the nucleus contains a "power center" and, accordingly, nucleons have orbital angular momenta relative to this "power center." Our approach does not predict the presence of such a "power center" in the nucleus.
nucl-th0 citations
03
Exact nuclear pairing solution for large-scale configurations: I. The EP (v1.0) program at zero temperature
Tran Quoc Viet · Le Tan Phuc · Tran Vu Dong · Nguyen Ngoc Anh · Nguyen Quang Hung
In this work, we present the ``EP code" (version 1.0), a user-friendly and robust computational tool. It computes the exact pairing eigenvalues and eigenvectors directly from the general nuclear pairing Hamiltonian, represented using SU(2) quasi-spin algebra with basis vectors in binary representation, at zero temperature for both odd and even deformed nucleon systems. In this initial release, the sparsity and symmetry of the pairing matrix are exploited for the first time to quickly construct the pairing matrix. The ARPACK and LAPACK packages are employed for the diagonalization of large- and small-scale sparse matrices, respectively. In addition, the calculation speed for odd nucleon systems is significantly improved by employing a novel technique to accurately identify the block containing the ground state in odd configurations. To ensure the high numerical stability, the Kahan compensation algorithm is employed. The current version of the EP code can efficiently expand the computational space to handle up to 26 doubly folded (deformed) single-particle levels and 26 nucleons on a standard desktop computer in approximately $1 0^{2}$ seconds with double precision. With sufficient computational resources, the code can process up to 63 deformed single-particle levels, which can accomodate from 1 to 63 nucleon pairs. The EP v1.0 code is also designed for future extensions, including the finite-temperature and parallel computations.
nucl-thComputer Physics Communications, 109906 (…·0 citations
04
Unraveling the anomaly in the production of $^{60}$ Fe nucleus in massive stars
Samapti Lakshan · Le Tan Phuc · Deepak Pandit · Srijit Bhattacharya · Le Thi Quynh Huong · Nguyen Dinh Dang · Balaram Dey · Nguyen Ngoc Anh · Nguyen Quang Hung
The production of $^{60}$ Fe is crucial for nucleosynthesis in massive stars and supernovae. In this work, by using the microscopic EP+IPM (exact pairing plus the independent-particle model) for the nuclear level density (NLD) and extended EP+PDM (exact pairing plus phonon damping model) for the $γ$ -ray strength function (gSF), we re-evaluate the substantial enhancement of $^{60}$ Fe production recently reported in {\it A. Spyrou et al., Nat. Comm. {\bf 15}, 9608 (2024)}, which was attributed to an unexpectedly large Maxwellian-averaged cross section (MACS). Our analysis demonstrates that this enhancement indeed originates from the choice of NLD, which, despite being constrained to reproduce the total NLD and gSF data, lacks a reliable spin dependence, a critical input for Hauser-Feshbach calculations of nuclear reaction rate. In contrast, our predictions yield a significantly lower MACS, calling the claimed enhancement into question. In particular, our approach highlights the microscopic nature of the low-energy enhancement of the gSF, the so-called upbend resonance, which arises from strong particle-particle ( $pp$ ) and hole-hole ( $hh$ ) excitations that emerge only at finite temperature, thereby further reinsisting on the invalidity of the Brink-Axel hypothesis in this low-energy region. Overall, our study reopens the question on the long-standing problem of $^{60}$ Fe production in massive stars.
nucl-thastro-ph.HEastro-ph.SR0 citations
05
Cross section calculation of T( $^{3}$ He, np) $^{4}$ He and (Ty $^{-}$ )( $^{3}$ He, npy $^{-}$ ) $^{4}$ He in the three-body dynamics
M.V. Egorov
This work presents three-body calculations of the cross sections for the $^{3}$ He+T $\to$ n+p+ $^{4}$ He fusion reaction. These calculations were performed by solving a set of six coupled Faddeev integral equations, utilizing a cluster representation of the target nucleus, the triton, as a bound neutron-deuteron system. Short-range interactions within the two-body subsystems included microscopic np, nd, n4He, and n3He scattering matrices, as well as phenomenological d3He models that allow for the coupling of the elastic channel with the d3He reaction channel. The roles of the d3He models and the Coulomb interaction between the 3He and T nuclei are briefly discussed. The resulting three-body reaction matrix was then utilized to estimate the role of a muon in the process $^{3}$ He+(Ty $^{-}$ ) $\to$ n+p+ $^{4}$ He+y $^{-}$ involving a Ty $^{-}$ atom, where y $^{-}$ in [ $e^{-}$ , $μ^{-}$ ]. It is demonstrated that the effect of cross-section enhancement induced by the muon's presence in the reaction zone is governed by a phase factor and persists in the first Born approximation for the exact four-body scattering matrix.
nucl-th0 citations
06
Modeling Ultra-High-Energy Cosmic Rays propagation using the input from Configuration Interaction Shell Model
O. Le Noan🇫🇷 · E. Khan🇧🇪 · S. Goriely🇫🇷 · K. Sieja🇫🇷
The dipole response of a nuclear system, characterized by its photon strength function (PSF), is a key ingredient of many applications of nuclear structure, ranging from nuclear reactor design and nuclear waste transmutation to astrophysical models of nucleosynthesis and stellar evolution. While the majority of those applications require the knowledge of PSF of mid-mass and heavy nuclei, there is now renewed interest in $E 1$ strength distributions of light nuclei in the framework of the PANDORA project, which aims at an understanding of the mass distribution of ultrahigh-energy cosmic radiation (UHECR).UHECR is of extragalactic origin and its interaction along the travel path is dominated by photoabsorption of cosmic background radiation boosted to the Giant Dipole Resonance (GDR) energy region in the center-of-mass system. Thus, systematic knowledge of the photoabsorption cross sections in light nuclei and of their subsequent particle decay is required. The purpose of this work is to enhance the database of available theoretical evaluations of PSF of light nuclei that are necessary in the studies of UHECR propagation. We employ the Configuration Interaction Shell Model (CI-SM) approach to provide predictions of $E 1$ dipole response for $p$ and $s d$ -shell nuclei, with mass number $A$ between 7 and 40. Theoretical predictions are compared to available data and to existing predictions from phenomenological and microscopic models. Finally, the impact of using of CI-SM PSF on the predicted propagation of a $^{40}$ Ca UHECR source is studied.
nucl-thastro-ph.HEPRC(2026)·1 citation
07
Unfolding Baryon Number Fluctuations from Correlations of Light Nuclei Production in Heavy-Ion Collisions
Yi-Heng Feng🇨🇳 · Che Ming Ko🇺🇸 · Xiaofeng Luo🇨🇳 · Yu-Gang Ma🇨🇳 · Kai-Jia Sun🇨🇳 · Song Zhang🇨🇳
Event-by-event fluctuations of the baryon number, which is mostly carried by protons and neutrons, in relativistic heavy-ion collisions provide a sensitive probe for locating the conjectured critical point in the quantum chromodynamics (QCD) phase diagram. Since current experiments have limited access to neutron fluctuations because detectors are largely insensitive to neutrons, measurements of (net-)proton fluctuations are often used as a proxy for (net-)baryon number fluctuations. Although direct measurements of neutron fluctuations are challenging, their information are encoded in the production and correlations of light nuclei, when they are formed through coalescence of nucleons at kinetic freeze-out. Here, we propose to unfold neutron fluctuations from correlations among light nuclei produced in heavy-ion collisions. Model calculations validate this approach and show that baryon number fluctuations can be unfolded up to the third order. For fourth and higher-order cumulants, however, the uncertainties become sizable, indicating that further methodological developments and refinements are required.
nucl-thPLB(2026)·1 citation
08
Constraining the nuclear equation of state from terrestrial experiments and neutron star observations using relativistic mean-field models
Tsuyoshi Miyatsu · Myung-Ki Cheoun · Kyungsik Kim · Koichi Saito
We investigate the nuclear equation of state (EoS) for isospin-asymmetric matter using a new set of RMF interactions with the $σ$ - $δ$ and $ω$ - $ρ$ mixing, referred to as the OMEG family. These interactions are optimized so as to reproduce both terrestrial nuclear measurements and astrophysical constraints extracted from NICER and GW170817. The $σ$ - $δ$ mixing softens the nuclear symmetry energy and pressure around twice the saturation density, which enables relatively small neutron-star radii and tidal deformabilities while keeping the nuclear EoS sufficiently stiff at high densities to support $2 M_{⊙}$ neutron stars. We find that the curvature parameter, $K_{sym}$ , plays an important role in realizing the soft-to-hard behavior of the nuclear EoS, and the astrophysical data favor small or even negative values of $K_{sym}$ .
nucl-thastro-ph.HEEPJ Web Conf.(2026)·0 citations
09
Relativistic superfluid profiles near critical surfaces
Lorenzo Gavassino🇬🇧 · Alexander Soloviev🇸🇮
Landau's two-fluid model of superfluidity ceases to apply in regions where the condensate amplitude exhibits rapid spatial variation, such as vortex cores or in the vicinity of container walls. A recently proposed relativistic Gross-Pitaevskii-type framework treats the condensate as an independent scalar degree of freedom, enabling a controlled analysis of such regimes. We use it to construct stationary superflows close to the superfluid-normal phase boundary, and examine their stability. We obtain an exact expression for Landau's critical velocity and show that the standard Newtonian profiles (such as the near-vortex condensate depletion or the boundary-layer decay) persist unmodified in the relativistic setting. We further analyse a genuinely relativistic configuration in which an accelerated superfluid develops a phase boundary induced by Tolman temperature gradients.
nucl-thcond-mat.quant-gasgr-qchep-th1 citation

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