Nuclear Theory·nucl-th

Thursday·April 17, 2025

9 papers—3 primary·6 cross-listed

01
Low-energy neutrino responses for 71Ga by electron capture rates, charge exchange reactions and shell model calculations
Yoritaka Iwata🇯🇵 · Hiroyasu Ejiri🇯🇵 · Shahariar Sarkar🇮🇳
Weak Gamow-Teller (GT) responses for low-lying states in $^{71} Ga$ are crucial for studying low-energy solar neutrinos and the Ga anomaly, i.e., the possible transition to the sterile state. The responses for the ground state, the first excited state, and the second excited state are evaluated for the first time using the experimental electron capture rates, the experimental charge exchange reaction (CER) rates corrected for the tensor-interaction effect and the theoretical interacting shell model (ISM) calculations. The contributions from the two excited states to the solar and $^{51} Cr$ neutrinos are found to be $4.2 \pm 1.2%$ of that for the ground state. This is slightly larger than the ISM values but little smaller than the CER values without corrections for the tensor interaction effect. The Ga anomaly is far beyond the uncertainty of the obtained nuclear responses.
nucl-thhep-phnucl-exPRC(2026)·0 citations
02
Moment of inertia for pair rotation: Interplay between order parameter and shell structure
Chisato Ruike · Nobuo Hinohara · Takashi Nakatsukasa
[Background] Pair condensation in finite nuclei generates a collective motion known as pair rotation. The moment of inertia of pair rotation (P-MoI) has been used as an indicator of pair condensation. [Purpose] We aim to elucidate the fundamental properties of the P-MoI, particularly its dependence on the particle number and the order parameter. [Method] The P-MoI was evaluated using the Bardeen-Cooper-Schrieffer (BCS) calculations with a monopole pairing Hamiltonian and Skyrme density functional theory calculations with different density-dependent pairing energy density functionals. [Results] In open-shell nuclei, a negative correlation was found between the P-MoI and the pair amplitude, which is the order parameter for the transition from the normal phase to the superconducting phase. Analysis based on the decomposition of the P-MoI into the orbital contributions within the BCS approximation shows that its orbital dependence is very similar to that of the pairing gap. [Conclusions] The P-MoI reflects the influence of both the level density near the Fermi energy and the pair amplitude.
nucl-th0 citations
03
Global $Λ$ polarization in heavy-ion collisions at high baryon density
Yu. B. Ivanov🇷🇺
Based on the model of three-fluid dynamics (3FD), the global $Λ$ polarization ( $P_{Λ}$ ) is calculated in Au+Au collisions at 3 $\leq s_{N N} \leq$ 9 GeV, in which high baryon density is achieved. Various contributions to $P_{Λ}$ are considered: those from the thermal vorticity, meson field, thermal shear and spin-Hall effect. Feed-down from higher-lying resonances is also taken into account. The results are compared with available data. Special attention is payed to the collision energies of $s_{N N} =$ 3, 3.2, 3.5, 3.9, and 4.5 GeV, for which a thorough scan of the energy, rapidity, and centrality dependence of $P_{Λ}$ is performed. The results for 3 GeV reasonably well reproduce the corresponding STAR data. While the results at $s_{N N} =$ 3.2, 3.5, 3.9, and 4.5 GeV can be considered as predictions for results of measurements within the STAR fixed-target (STAR-FXT) programthat are expected in the nearest future. It is predicted that a broad maximum of $P_{Λ}$ is reached at $s_{N N} \approx$ 3--3.9 GeV, exact position of which depends on the centrality and width of the midrapidity range of observation. Impact of the meson-field, thermal-shear and spin-Hall-effect contributions to $P_{Λ}$ is also studied.
nucl-thhep-phnucl-exPRC(2025)·4 citations
04
$R$ -matrix type parametrization of the Jost function for extracting the resonance parameters from scattering data
P. Vaandrager · M.L. Lekala · S.A. Rakityansky
A new method is proposed for fitting non-relativistic binary-scattering data and for extracting the parameters of possible quantum resonances in the compound system that is formed during the collision. The method combines the well-known $R$ -matrix approach with the analysis based on the semi-analytic representation of the Jost functions. It is shown that such a combination has the advantages of both these approaches, namely, the number of the fitting parameters remains relatively small (as for the $R$ -matrix approach) and the proper analytic structure of the $S$ -matrix is preserved (as for the Jost function method). It is also shown that the new formalism, although closely related to the $R$ -matrix method, has the benefit of no dependence on an arbitrary channel radius. The efficiency and accuracy of the proposed method are tested using a model single-channel potential. Artificial ``experimental'' data generated with this potential are fitted, and its known resonances are successfully recovered as zeros of the Jost function on the appropriate sheet of the Riemann surface of the energy.
↳ quant-phnucl-thEPJA(2025)·0 citations
05
Quasi-particle hydrodynamics with momentum-dependent relaxation time
Arghya Mukherjee🇮🇳 · Samapan Bhadury🇵🇱 · Pracheta Singha🇷🇴
We formulate the relativistic dissipative hydrodynamics of a system of quasi-particles from the Boltzmann equation within the ambit of relaxation time approximation with modified collision kernels. We focus on two specific scenarios with single quasi-particle species, (i) the extended relaxation time approximation, and (ii) the novel relaxation time approximation. We find that both approaches lead to equivalent results up to first-order in spacetime gradients. We generalize the extended relaxation time approach to incorporate multiple quasi-particle species and obtain the corresponding expressions for the shear ( $η_{s}$ ) and bulk ( $ζ_{s}$ ) viscous coefficients. As an application, we study the temperature dependence of the transport coefficients of hot QCD medium with quasi-gluon and (light and strange) quasi-quark sectors considering the power law ansatz for the momentum dependence of the relaxation time. We explore the impact of the power law exponent on the ratio $ζ_{s} / η_{s}$ . Our study suggests that in comparison to a constant exponent, a temperature dependent exponent in the power law ansatz is more suitable for modeling the quasi-particle dynamics in the relevant temperature regime of heavy ion collision.
↳ hep-phnucl-thPRD(2025)·4 citations
06
Quantum simulations of nuclear resonances with variational methods
Ashutosh Singh🇮🇳 · Pooja Siwach🇺🇸 · P. Arumugam🇮🇳
The many-body nature of nuclear physics problems poses significant computational challenges. These challenges become even more pronounced when studying the resonance states of nuclear systems, which are governed by the non-Hermitian Hamiltonian. Quantum computing, particularly for quantum many-body systems, offers a promising alternative, especially within the constraints of current noisy intermediate-scale quantum (NISQ) devices. This work aims to simulate nuclear resonances using quantum algorithms by developing a variational framework compatible with non-Hermitian Hamiltonians and implementing it fully on a quantum simulator. We employ the complex scaling technique to extract resonance positions classically and adapt it for quantum simulations using a two-step algorithm. First, we transform the non-Hermitian Hamiltonian into a Hermitian form by using the energy variance as a cost function within a variational framework. Second, we perform theta-trajectory calculations to determine optimal resonance positions in the complex energy plane. To address resource constraints on NISQ devices, we utilize Gray Code (GC) encoding to reduce qubit requirements. We first validate our approach using a schematic potential model that mimics a nuclear potential, successfully reproducing known resonance energies with high fidelity. We then extend the method to a more realistic alpha-alpha nuclear potential and compute the resonance energies with a basis size of 16, using only four qubits. This study demonstrates, for the first time, that the complete theta-trajectory method can be implemented on a quantum computer without relying on any classical input beyond the Hamiltonian. The results establish a scalable and efficient quantum framework for simulating resonance phenomena in nuclear systems. This work represents a significant step toward quantum simulations of open quantum systems.
↳ quant-phnucl-thPRC(2025)·14 citations
07
Advancing quantum simulations of nuclear shell model with noise-resilient protocols
Nifeeya Singh🇮🇳 · Pooja Siwach🇺🇸 · P. Arumugam🇮🇳
Some of the computational limitations in solving the nuclear many-body problem could be overcome by utilizing quantum computers. The nuclear shell-model calculations providing deeper insights into the properties of atomic nuclei, is one such case with high demand for resources as the size of the Hilbert space grows exponentially with the number of particles involved. Quantum algorithms are being developed to overcome these challenges and advance such calculations. To develop quantum circuits for the nuclear shell-model, leveraging the capabilities of noisy intermediate-scale quantum (NISQ) devices. We aim to minimize resource requirements (specifically in terms of qubits and gates) and strive to reduce the impact of noise by employing relevant mitigation techniques. We achieve noise resilience by designing an optimized ansatz for the variational quantum eigensolver (VQE) based on Givens rotations and incorporating qubit-ADAPT-VQE in combination with variational quantum deflation (VQD) to compute ground and excited states incorporating the zero-noise extrapolation mitigation technique. Furthermore, the qubit requirements are significantly reduced by mapping the basis states to qubits using Gray code encoding and generalizing transformations of fermionic operators to efficiently represent manybody states. By employing the noise-resilient protocols, we achieve the ground and excited state energy levels of 38Ar and 6Li with better accuracy. These energy levels are presented for noiseless simulations, noisy conditions, and after applying noise mitigation techniques. Results are compared for Jordan Wigner and Gray code encoding using VQE, qubit-ADAPT-VQE, and VQD. Our work highlights the potential of noise-resilient protocols to leverage the full potential of NISQ devices in scaling the nuclear shell model calculations.
↳ quant-phnucl-thPRC(2025)·14 citations
08
Charge radii of neutron-rich scandium isotopes and the seniority symmetry in the $0 f_{7/2}$ shell
S. W. Bai🇨🇳 · X. F. Yang🇨🇳 · Á. Koszorús🇧🇪 · J. C. Berengut🇦🇺 · J. Billowes🇬🇧 · M. L. Bissell🇬🇧 · K. Blaum🇩🇪 · A. Borschevsky🇳🇱 · P. Campbell🇬🇧 · B. Cheal🇬🇧 · C. S. Devlin🇬🇧 · K. T. Flanagan🇬🇧 and 21 other authors
Nuclear charge radii of neutron-rich $^{47 - 49}$ Sc isotopes were measured using collinear laser spectroscopy at CERN-ISOLDE. The new data reveal that the charge radii of scandium isotopes exhibit a distinct trend between $N = 20$ and $N = 28$ , with $^{41}$ Sc and $^{49}$ Sc isotopes having similar values, mirroring the closeness of the charge radii of $^{40}$ Ca and $^{48}$ Ca. Theoretical models that successfully interpret the radii of calcium isotopes could not account for the observed behavior in scandium radii, in particular the reduced odd-even staggering. Remarkably, the inclusion of the new $^{49}$ Sc radius data has unveiled a similar trend in the charge radii of $N = 28$ isotones and $Z = 20$ isotopes when adding the neutrons atop the $^{40}$ Ca core and the protons atop the $^{48}$ Ca core, respectively. We demonstrate that this trend is consistent with the prediction of the seniority model.
↳ nucl-exnucl-thPRL(2025)·20 citations
09
Suppression of composition $g$ -modes in chemically-equilibrating warm neutron stars
Tianqi Zhao🇺🇸 · Peter B. Rau🇺🇸 · Alexander Haber🇬🇧 · Steven P. Harris🇺🇸 · Constantinos Constantinou🇮🇹 · Sophia Han🇺🇸
We investigate the impact of chemical equilibration and the resulting bulk viscosity on non-radial oscillation modes of warm neutron stars at temperatures up to $T \approx 5$ MeV, relevant for protoneutron stars and neutron-star post-merger remnants. In this regime, the relaxation rate of weak interactions becomes comparable to the characteristic frequencies of composition $g$ -modes in the core, resulting in resonant damping. To capture this effect, we introduce the dynamical sound speed, a complex, frequency-dependent generalization of the adiabatic sound speed that encodes both the restoring force and the dissipative effects of bulk compression. Using realistic weak reaction rates and three representative equations of state, we compute the complex frequencies of composition $g$ -modes with finite-temperature profiles. We find that bulk viscous damping becomes increasingly significant with temperature and can completely suppress composition $g$ -modes. In contrast, the $f$ -mode remains largely unaffected by bulk viscosity due to its nearly divergence-free character. Our results highlight the sensitivity of $g$ -mode behavior to thermal structure, weak reaction rates, and the equation of state, and establish the dynamical sound speed as a valuable descriptor characterizing oscillation properties in dissipative neutron star matter.
↳ astro-ph.HEgr-qcnucl-thApJ(2025)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE