Nuclear Theory·nucl-th

Wednesday·May 21, 2025

12 papers—4 primary·8 cross-listed

01
Unified nonparametric equation-of-state inference from the neutron-star crust to perturbative-QCD densities
Eliot Finch🇺🇸 · Isaac Legred🇺🇸 · Katerina Chatziioannou🇺🇸 · Reed Essick🇨🇦 · Sophia Han🇨🇳 · Philippe Landry🇨🇦
Perturbative quantum chromodynamics (pQCD), while valid only at densities exceeding those found in the cores of neutron stars, could provide constraints on the dense-matter equation of state (EOS). In this work, we examine the impact of pQCD information on the inference of the EOS using a nonparametric framework based on Gaussian processes (GPs). We examine the application of pQCD constraints through a "pQCD likelihood," and verify the findings of previous works; namely, a softening of the EOS at the central densities of the most massive neutron stars and a reduction in the maximum neutron-star mass. Although the pQCD likelihood can be easily integrated into existing EOS inference frameworks, this approach requires an arbitrary selection of the density at which the constraints are applied. The EOS behavior is also treated differently on either side of the chosen density. To mitigate these issues, we extend the EOS model to higher densities, thereby constructing a "unified" description of the EOS from the neutron-star crust to densities relevant for pQCD. In this approach the pQCD constraints effectively become part of the prior. Since the EOS is unconstrained by any calculation or data between the densities applicable to neutron stars and pQCD, we argue for maximum modeling flexibility in that regime. We compare the unified EOS with the traditional pQCD likelihood, and although we confirm the EOS softening, we do not see a reduction in the maximum neutron-star mass or any impact on macroscopic observables. Though residual model dependence cannot be ruled out, we find that pQCD suggests the speed of sound in the densest neutron-star cores has already started decreasing toward the asymptotic limit; we find that the speed of sound squared at the center of the most massive neutron star has an upper bound of $\sim 0.5$ at the $90%$ level.
nucl-thastro-ph.HEgr-qcPRD(2025)·15 citations
02
Searching for entanglement in final polarization states of the neutron-proton scattering
H. Witała🇵🇱 · J. Golak🇵🇱 · R. Skibiński🇵🇱
We investigate polarization states of the outgoing neutron-proton ( $n p$ ) pair in elastic polarized neutron and proton scattering, aiming to find unambiguous evidence for entanglement of their spin states. To obtain complete information about these states, we calculate, using the high precision nucleon-nucleon potential AV18, the final polarizations of the neutron and proton as well as their spin correlation coefficients, which unequivocally define the corresponding spin density matrix. We compute all terms contributing to polarizations and spin correlations, e.g. not only induced polarizations and correlations resulting from unpolarized $n p$ scattering, but also contributions from single polarization and correlation transfers from individual polarized incoming nucleons, and, for the first time, allotment to both quantities stemming from a doubly spin polarized initial state. We find that for the most part the final spin states are statistical mixture of states.The only pure states occur for highly polarized incoming neutrons and protons with maximal polarizations. By quantifying the degree of entanglement through entanglement power and concurrence, we observed that the entanglement of impure final states increases with energy. Among the pure spin states resulting from incoming states with maximal neutron and proton polarizations, we found, at $E_{l ab} = 100$ ~MeV, cases of strongly entangled Bell-type states with only a small admixture of entanglement-spoiling contributions.
nucl-thPRC(2025)·9 citations
03
Classifying metal-poor stars with machine learning using nucleosynthesis calculations
Nicole Vassh · Yilin Wang · Richard M. Woloshyn · Michelle P. Kuchera · Maude Lariviere · Kayle Majic · Benoit Cote
We apply the capabilities of machine learning (ML) to discern patterns in order to classify metal-poor stars. To do so, we train an ML model on a bank of nucleosynthesis calculations derived from hydrodynamic simulations for events such as neutron star mergers where the rapid ( $r$ ) neutron capture process can take place. Likewise we consider a bank of calculations from simulations of the slow ( $s$ ) neutron capture process and also consider a few calculations for the intermediate ( $i$ ) neutron capture process. We demonstrate that the ML does well overall in recognizing the $s$ process from the $r$ process, and after training on theoretical calculations ML stellar assignments match conventional labels 87% of the time. We highlight that this method then points to stars that could benefit from additional observational measurements. We also demonstrate that the ML assigns some of the presently considered $i$ -process stars to instead be of $r$ or $s$ in origin, but likewise, finds stars currently labeled as $s$ to be potentially more aligned with $i$ enrichment. This first application of ML to classify metal-poor star enrichment using theoretical nucleosynthesis calculations thus reveals the promise, and some challenges, associated with this new data-driven path forward.
nucl-thastro-ph.GAastro-ph.SRApJ(2025)·0 citations
04
Left-right splitting of elliptic flow in heavy ion collisions: TRENTo-3D initialization and CLVisc hydrodynamic simulations
Ze-Fang Jiang🇨🇳 · Xiang Fan🇨🇳 · Duan She🇨🇳 · Shasha Ye🇨🇳 · Ben-Wei Zhang🇨🇳
Using the TRENTo-3D initial condition model coupled with (3+1)-dimensional CLVisc hydrodynamic simulations, we systematically investigate the left-right splitting of elliptic flow ( $Δ v_{2}$ ) for soft particles in relativistic heavy-ion collisions. Our study reveals that the final distribution characteristics of $Δ v_{2}$ are primarily depend on the odd flow harmonics and $v_{2}$ itself. We find that the parton transverse momentum scale $k_{T}$ not only determines the geometric tilt of the QGP fireball but also significantly affects the rapidity dependence of both $v_{1}$ and $Δ v_{2}$ , providing new insights into the splitting mechanism of $Δ v_{2}$ . Furthermore, our results demonstrate that $Δ v_{2} (p_{T})$ exhibits significant sensitivity to influences such as the sub-nucleonic degrees of freedom (or `hotspots'), transverse momentum scale, and fragmentation region profile. By analyzing the $Δ v_{2}$ and $Δ v_{2} / v_{2}$ ratio, our findings provide new constraints on the uncertainties of the QGP initial state and provide additional constraints for refining model parameters.
nucl-thhep-phPRC(2025)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Unified nonparametric equation-of-state inference from the neutron-star crust to perturbative-QCD densities

Searching for entanglement in final polarization states of the neutron-proton scattering

Classifying metal-poor stars with machine learning using nucleosynthesis calculations

Left-right splitting of elliptic flow in heavy ion collisions: TRENTo-3D initialization and CLVisc hydrodynamic simulations

Affiliations