Nuclear Theory·nucl-th

Tuesday·June 17, 2025

24 papers—10 primary·14 cross-listed

01
Impact of particle production mechanisms on pseudorapidity distribution and directed flow in Au+Au and Cu+Cu collisions at $s_{N N}$ = 19.6 GeV using AMPT model
Muhammad Farhan Taseer🇨🇳 · Subhash Singha🇨🇳
The STAR experiment at the top RHIC energy has observed that the directed flow ( $v_{1}$ ) of inclusive light hadrons is independent of the collision system size at a given centrality~\cite{STAR:2008jgm}. However, recent STAR measurements indicate a system-size dependence in the $v_{1} (y)$ -slope ( $d v_{1} / d y$ ) of protons, antiprotons, and their differences ( $Δ d v_{1} / d y$ ) at a given centrality, suggesting a potential influence of baryon production and transport mechanisms~\cite{Taseer:SQM2024talk}. We have studied pseudorapidity ( $d N / d y$ ) distributions and directed flow ( $v_{1}$ and $d v_{1} / d y$ ) for pions, kaons, and protons in Au+Au and Cu+Cu collisions at $s_{N N} = 19.6$ GeV using the A Multi-Phase Transport (AMPT) model. Specifically, we investigated the influence of string junction parameters in AMPT via the PYTHIA/JETSET routines, focusing on the popcorn mechanism and string-splitting parameters, on $d N / d y$ , $d v_{1} / d y$ , and their charge-dependent splittings ( $Δ d N / d y$ and $Δ d v_{1} / d y$ ). We observe that string junction parameters can affect $d N / d y$ , $d v_{1} / d y$ , $Δ d N / d y$ , and $Δ d v_{1} / d y$ for $π$ , K, and p, and influence their system-size dependence. The effect is most prominent on the $v_{1}$ of protons, non-trivial for kaons, while the pions $v_{1}$ remain largely unchanged. These findings provide insights into the interplay between particle production mechanisms, baryon transport, and directed flow in heavy-ion collisions.
nucl-thhep-exhep-phnucl-exCPC(2025)·0 citations
02
Imprint of $α$ -Clustering on Ab Initio Correlations in Relativistic Light Ion Collisions
Hadi Mehrabpour🇨🇳
This study investigates the influence of $α$ -cluster structures in relativistic light nuclear collisions. Using a cluster framework, I extract the characteristics of the nucleonic configurations of $^{16}$ O and $^{20}$ Ne as predicted by various \textit{ab-initio} models, including Nuclear Lattice Effective Field Theory (NLEFT), Variational Monte Carlo (VMC), and the Projected Generator Coordinate Method (PGCM). Additionally, I analyze configurations derived from a three-parameter Fermi (3pF) density function. The investigation focuses on the effects of cluster parameters on two-point correlators using a rotor model for symmetric collisions ( $^{16}$ O+ $^{16}$ O and $^{20}$ Ne+ $^{20}$ Ne) and asymmetric collisions ( $^{208}$ Pb+ $^{16}$ O and $^{208}$ Pb+ $^{20}$ Ne). The cluster parameters are determined by minimizing the \textit{chi-square} statistic to align the nucleon distributions with those predicted by the aforementioned theories. The results reveal that perturbative calculations effectively capture the structural features of these nuclei, while comparisons with Monte Carlo simulations validate these findings. Furthermore, the analysis reveals distinct cluster geometries: VMC suggests tetrahedral shapes, while NLEFT, PGCM, and 3pF indicate irregular triangular pyramids. Notably, NLEFT shows a bowling pin-like $α$ cluster structure for $^{20}$ Ne. The study also identifies constraints on cluster parameters in the different oxygen structures, with a gradual increase in $ε_{2} {2}$ for the states of $α$ + $^{12}$ C. Accurate modeling of asymmetric collisions necessitates a range of nucleons from heavy spherical nuclei, leading to weighted correlators in perturbative calculations. I demonstrate consistency between perturbative calculations and Monte Carlo models, with analytical calculations providing more insights into asymmetric than symmetric collisions.
nucl-thhep-thPRC(2026)·9 citations
03
Sign-Problem-Free Nuclear Quantum Monte Carlo Simulation
Zhong-Wang Niu🇨🇳 · Bing-Nan Lu🇨🇳
Quantum Monte Carlo (QMC) methods offer exact solutions for quantum many-body systems but face severe limitations in fermionic systems like atomic nuclei due to the sign problem. While sign-problem-free QMC algorithms exist and provide valuable insights across disciplines, they have been restricted to simple models with limited quantitative predictive power. Here we overcome this barrier by developing a novel lattice nuclear force that is rigorously sign-problem-free for even-even nuclei. This interaction achieves a standard deviation of $σ = 2.932$ MeV from experimental binding energies for 76 even-even nuclei ( $N, Z \leq 28$ ), matching state-of-the-art phenomenological mean-field models. Key innovations include the first sign-problem-free implementation of spin-orbit coupling for shell evolutions and an efficient QMC-optimized framework for global parameter fitting. Using this approach, we compute binding energies from $^{4}$ He to $^{132}$ Sn with unprecedented one-thousandth level numerical precision, reproduce symmetric nuclear matter saturation, and reveal novel spin-orbit-driven clustering in light nuclei. This work transforms sign-problem-free QMC into a scalable and predictive nuclear structure tool, while establishing a high-fidelity, non-perturbative foundation for \textit{ab initio} calculations of heavy nuclei.
nucl-thhep-latPRL(2025)·20 citations
04
Evolution of energy density fluctuations in the presence of a magnetic field
Shreyansh S. Dave🇮🇳 · Subrata Pal🇮🇳
In this proceeding, we study the evolution of energy density fluctuations in the presence of a static and uniform magnetic field. By numerically solving the relativistic Boltzmann-Vlasov equation within the relaxation time approximation and performing the momentum mode analysis of different wavelength fluctuations, we show that the magnetic field increases the damping of mode oscillations. This causes a qualitative change in the fluctuations present in the system at the timescale required to achieve a local equilibrium state.
nucl-thhep-phhep-thJ.Subatomic Part.Cosmol.(2025)·0 citations
05
Application of the optimized-basis generator coordinate method to low-lying excited states of sd-shell nuclei
Moemi Matsumoto · Yusuke Tanimura · Kouichi Hagino
We apply the optimized-basis generator coordinate method (OptGCM) to sd-shell nuclei, $^{20}$ Ne, $^{24}$ Mg, and $^{28}$ Si. This method variationally optimizes both the basis Slater determinants in the generator coordinate method (GCM) and the corresponding weight coefficients. To analyze the low-lying excited states of those nuclei, we implement the angular momentum projection. With the Skyrme interaction, we show that the simultaneous optimzation of the basis functions and the weight factors lowers the energy of the excited states and at the same time leads to an appreciable effect on transition probabilities. These results highlight the effectiveness of the OptGCM method.
nucl-thPRC(2025)·1 citation
06
$0 ν β β$ decay nuclear matrix elements under Left-Right symmetric model from the spherical quasi-particle random phase approximation method with realistic force
Ri-Guang Huang🇨🇳 · You-Cai Chen🇨🇳 · Dong-Liang Fang🇨🇳
We perform the calculation of nuclear matrix elements for the neutrinoless double beta decays under a Left-Right symmetric model mediated by light neutrino, and we adopt the spherical quasi-particle random-phase approximation (QRPA) approach with realistic force. For eight nuclei: $^{76}$ Ge, $^{82}$ Se, $^{96}$ Zr, $^{100}$ Mo, $^{116}$ Cd, $^{128}$ Te, $^{130}$ Te and $^{136}$ Xe, related nuclear matrix elements are given. We analyze each term and the details of contributions of different parts are also given. For the $q$ term, we find that the weak-magnetism components of the nucleon current contribute equally as other components such as axial-vector. We also discuss the influence of short-range correlations on these NMEs. It is found that $R$ term are more sensitive to the short range correlation than other terms due to the large portion of the contribution from high exchange momenta.
nucl-thCPC(2026)·1 citation
07
Kadanoff-Baym approach to bound states in open quantum systems
Tim Neidig🇩🇪 · Marcus Bleicher🇩🇪 · Hendrik van Hees🇩🇪 · Carsten Greiner🇩🇪
In this paper, we extend the method of Kadanoff-Baym equations for open quantum systems to arbitrary kinds of systems and heat baths, either fermionic or bosonic. This includes three spacial dimensions and different potentials for the system-bath interaction or external traps. We study the quantum-mechanical formation of bound states in one and also in three dimensions with the full Kadanoff-Baym equations and compare them to more simplified approaches with and without memory effects. An in-depth examination of the thermodynamics of open systems is performed, showing perfect equilibration of the system's degrees of freedom along with a comprehensive investigation of the influence of the heat bath on the system's wave functions. The formation time, decay time and regeneration of bound states and their dependence on the temperature and coupling strength is explored We evaluate the non-equilibrium Kadanoff-Baym equations for the system particles, assuming that interactions are elastic two-particle collisions with the heat-bath particles. Finally, we describe in detail the method used to numerically solve the corresponding spatially heterogeneous integro-differential equations for the set of one-particle Green's functions.
nucl-thPRC(2025)·1 citation
08
Hot pygmy dipole strength in nickel isotopes
Amandeep Kaur · Esra Yüksel · Nils Paar
At finite temperatures, nuclear excitations are significantly modified, most notably through the emergence of additional low-energy dipole strength, which can critically impact astrophysical reaction rates. Ongoing fusion-evaporation experiments on Ni isotopes provide a unique opportunity to investigate the hot pygmy dipole strength (HPDS), underscoring the need for reliable theoretical predictions and a comprehensive understanding of this emerging phenomenon. In this work, the HPDS is investigated in Ni isotopes from $N = Z$ to neutron-rich systems ( $^{56 - 70}$ Ni) over a temperature range of $T =$ 0 $-$ 2~MeV using the finite-temperature relativistic quasiparticle random phase approximation. In neutron-rich Ni isotopes, the pygmy dipole strength at higher temperatures exceeds up to 2.5 times its value observed at zero temperature. In contrast, near $N \approx Z$ isotopes show negligible low-energy dipole strength at $T = 0$ MeV but develop a pronounced HPDS as the temperature increases. Predicted E1 energy-weighted strength ( $S_{EWS}$ ) and cumulative $B$ (E1) values for HPDS are presented across the Ni isotopic chain for various low-energy intervals and temperatures, providing essential benchmarks to support and guide experimental studies.
nucl-thPRC(2025)·1 citation
09
Constraints on $Λ N$ Effective Interactions from Mirror Hypernuclei in a Deformed Relativistic Hartree-Bogoliubov Model
Yu-Ting Rong🇨🇳 · Dan Yang🇨🇳 · Cheng-Jun Xia🇨🇳 · Ting-Ting Sun🇨🇳
We investigate the ground-state properties of four mirror hypernuclei pairs-- $_{Λ}^{10}$ Be- $_{Λ}^{10}$ B, $_{Λ}^{12}$ B- $_{Λ}^{12}$ C, $_{Λ}^{16}$ N- $_{Λ}^{16}$ O, and $_{Λ}^{40}$ K- $_{Λ}^{40}$ Ca--within the deformed relativistic Hartree-Bogoliubov framework, analyzing their connection to $Λ N$ effective interactions. Systematic calculations with eight distinct effective interactions reveal linear correlations between mirror hypernuclei in $Λ$ separation energies and charge radii. The charge symmetry breaking effects, quantified through $Λ$ separation energy differences, exhibit a positive correlation with the SU(3) flavor symmetry violation. We emphasize that constraints derived from $A = 10$ and $A = 12$ hypernuclear pairs must explicitly incorporate rotational energy correction effects. Precision measurements of the (near) spherical $A = 16$ and $A = 40$ mirror systems are proposed as critical benchmarks for refining the isospin part of the hyperon-nucleon interactions.
nucl-th2 citations
10
Two-neutrino $0^{+} \to 0^{+}$ double beta decay of $^{48} Ca$ within the DFT-NCCI framework
Jan Miśkiewicz🇵🇱 · Maciej Konieczka🇵🇱 · Wojciech Satuła🇵🇱
We present a seminal calculation of the nuclear matrix element for the two-neutrino double beta ( $2 ν β β$ ) decay of $^{48} Ca \to^{48} Ti$ using a post-Hartree-Fock (HF) Density Functional Theory-based No-Core Configuration-Interaction (DFT-NCCI) framework developed by our group [Phys. Rev. C 94, 024306 (2016)]. In the present calculation, we utilize a variant of the approach that restores rotational symmetry and mixes states projected from self-consistent mean-field configurations obtained by solving the HF equations with the density-independent local Skyrme interaction. Our calculations yield $∣ M_{2 ν β β} ∣ = 0.056 (6)$ MeV $^{- 1}$ for the nuclear matrix element describing this process. This result is in very good agreement with shell-model studies - for example, with the calculations by Horoi {\it et al.\/} [Phys. Rev. C 75, 034303 (2007)], which yielded 0.054 (0.064) MeV $^{- 1}$ for the GXPF1A (GXPF1) interactions, respectively. It is also in a reasonable agreement with the most recent experimental estimate from the review by Barabash, which is 0.068(6) MeV $^{- 1}$ , assuming quenching $q g_{A} \approx 1$ . The consistency of our prediction with the shell-model results increases our confidence in the nuclear modeling of this second-order, very rare process which is of paramount importance for further modeling of the neutrinoless double beta ( $0 ν β β$ ) decay process.
nucl-thPRC(2025)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE