Nuclear Theory·nucl-th

Friday·February 27, 2026

17 papers—9 primary·8 cross-listed

01
Impact of Geometric Inflation on Nucleon Size Sensitivity in Relativistic Heavy-Ion Collisions
Jian-fei Wang🇨🇳 · Hao-jie Xu🇨🇳
The intrinsic transverse size of nucleons, parameterized by a Gaussian width $w$ , is a critical yet uncertain input in the initial-state modeling of relativistic heavy-ion collisions. Using a finite $w$ in standard initial geometry models introduces an unintentional ``geometric inflation'' that alters the initial nuclear density profile. In this study, we implement a self-consistent density correction to eliminate this artifact and investigate its impact on final-state observables. Through hybrid (viscous hydrodynamics + hadronic transport) simulations of $^{208}$ Pb+ $^{208}$ Pb collisions at the LHC, we demonstrate that removing geometric inflation significantly modifies the sensitivity of observables to the nucleon width $w$ . While elliptic flow and mean transverse momentum ( $⟨[p_{T}]⟩$ ) become less sensitive to variations in $w$ , the Pearson correlation coefficient $ρ (v_{n}^{2}, δ p_{T})$ , $[p_{T}]$ fluctuations, and triangular flow exhibit enhanced sensitivity to fluctuations in nucleon positions. Our results indicate that uncorrected geometric inflation can bias the extraction of nucleon structure and quark-gluon plasma properties. This underscores the necessity of a self-consistent initial-state geometry for reliable Bayesian inference in heavy-ion collisions.
nucl-thnucl-ex0 citations
02
The shape of transverse momentum spectra in hybrid hydrodynamic models
Thiago S. Domingues🇧🇷 · Fernando G. Gardim🇧🇷 · Cicero D. Muncinelli🇧🇷 · Andre V. Giannini🇵🇹 · Gabriel S. Denicol🇧🇷 · Tiago Nunes da Silva🇧🇷 · David D. Chinellato🇦🇹 · Giorgio Torrieri🇧🇷 · Mauricio Hippert🇧🇷 · Jun Takahashi🇧🇷 · Matthew Luzum🇧🇷
We study the scaled transverse momentum spectra over a wide parameter space of state-of-the-art hydrodynamic simulation models in order to learn what information can be obtained from the shape of identified-particle spectra -- previously observed to be surprisingly universal across centrality and collision systems in both experimental data and hydrodynamic simulations. We study its sensitivity to each of 17 model parameters in the context of 4 different models for particlization when switching from the hydro description to the kinetic theory afterburner. We find that the strongest sensitivity is to parameters relating to bulk viscosity, free-streaming time, and the $\texttt{T$ _\mathrm{R} $ENTo}$ nucleon width parameter $w$ . However, we find that the model generally has surprisingly little flexibility in describing the scaled spectrum observable, despite the large number of parameters. Within this small range of parameter dependence, we further find significant tension in a simultaneous description of momentum-integrated observables. In particular, while the mean transverse momentum prefers a large value of the nucleon width parameter $w$ , a small value is required to obtain scaled spectra that are consistent with experimental measurements. We speculate on the origin of these model tensions and possible missing physics in the commonly-used $\texttt{T$ _\mathrm{R} $ENTo}$ +free streaming+hydro+afterburner simulation model.
nucl-thhep-phhep-th2 citations
03
Symmetry-imposed correlation in nuclear level statistics: The spin distribution
Junchao Guo · Yang Sun
Despite long-term research, the origin of spin cutoff in the angular-momentum (spin) distribution of nuclear level densities remains incompletely elucidated. We demonstrate that this problem can be traced back to Bethe's assumption that nucleons in finite Fermi systems are independent random variables. By constructing a statistical ensemble that enforces rotational invariance through angular-momentum coupling, we obtain an analytical expression for the spin cutoff parameter, which includes a previously unidentified finite-population correction. Our results show that, even in the absence of interactions, nuclear many-body states exhibit non-negligible correlations arising from fermionic antisymmetry and angular-momentum coupling. From this perspective, spin cutoff may be interpreted as a quantitative measure of correlation imposed by symmetry in nuclear level statistics.
nucl-th0 citations
04
Statistical properties of non-flow correlations in pp and heavy-ion collisions at RHIC energies
Satya Ranjan Nayak🇮🇳 · Akash Das🇮🇳 · B.K. Singh🇮🇳
In this work, we have studied the two-particle cumulant in pp, d-Au, and Au-Au collisions. The two-particle cumulant was treated as an event-by-event distribution, and its skewness and kurtosis were analyzed. The non-flow correlations, like jets and decays, constantly produced a skewed distribution, regardless of the model used. On the contrary, HYDJET++ produced a smooth Gaussian distribution at higher $η$ windows in fixed impact parameter collisions. The skewness increased consistently for higher $η$ windows in all non-QGP models like PYTHIA, PHOJET, QGSJET, and DPMJET. The kurtosis of the distribution also increased with $η$ windows in non-QGP models. The skewness and kurtosis of the distributions produced by HYDJET++ decreased with $Δ η$ and eventually reached zero at higher $Δ η$ .
nucl-thhep-ph0 citations
05
Space-time regions of high baryon density and baryon stopping in heavy-ion collisions
Yuri B. Ivanov🇷🇺
Four-volumes ( $V_{4} =$ spatial-3-volume $\times$ lifetime) are calculated within the model of three-fluid dynamics (3FD) and compared with those of the the JET AA Microscopic Transport Model (JAM). The calculations are performed for central Au+Au collisions at energies $s_{N N} =$ 3 -- 19.6 GeV. These $V_{4}$ indicate optimal collision-energy ranges for realizing macroscopic high baryon-density matter. It is found that the 3FD four-volumes noticeably exceed those in the JAM, which indicates a stronger baryon stopping in the 3FD model as compared to that JAM. It is argued that this difference in the baryon stopping correlates with stiffness of the EoS implemented in these models. Contrary to JAM, the four-volume, where a baryon density ( $n_{B}$ ) exceeds three times the normal nuclear density ( $n_{0}$ ), does not exhibit a maximum as a function of $s_{N N}$ . It decreases monotonically with increasing $s_{N N}$ , remaining at a fairly macroscopic level (i.e. $V_{4} \geq 5. 5^{4}$ fm $^{4}$ /c). For higher baryon densities, $V_{4}$ exhibits maxima in its dependence on $s_{N N}$ . The optimal energy range for densities $n_{B} / n_{0} >$ 4 is located at $s_{N N} =$ 3.2 -- 8 GeV. Even for $n_{B} / n_{0} >$ 6, the four-volume remains quite macroscopic ( $V_{4} \geq 4^{4}$ fm $^{4}$ /c) at $s_{N N} =$ 4.5 -- 9 GeV contrary to the JAM.
nucl-thhep-phPRC(2026)·1 citation
06
CREX and PREX-II reconciled within energy-density functional theory
P. Papakonstantinou
The CREX and PREX-II measurements of the neutron-skin thickness of 48Ca and 208Pb challenge standard nuclear energy-density functional (EDF) descriptions of nuclei and nuclear matter. We show that the apparent tension arises from an implicit constraint in EDF theory, which ties the density dependence of the functional at the dilute nuclear surface to that of uniform matter near saturation. Relaxing this surface-bulk coupling and independently constraining the dilute-density sector, while preserving realistic saturation and high-density behavior, yields EDFs that simultaneously reproduce the neutron skins of both nuclei, their electric dipole polarizabilities, and neutron-star mass-radius relations. The established correlation between the neutron-skin thickness and the symmetry-energy slope parameter L at saturation is retained but becomes substantially broader. The results show that current neutron-skin data do not require extreme values of L and highlight an underconstrained degree of freedom associated with low-density nuclear matter.
nucl-th1 citation
07
Towards a microscopic description of 12C+12C fusion at stellar energies
P. Descouvemont
I present a fully microscopic description of the 12C+12C fusion reaction at stellar energies. Utilizing the multichannel Resonating Group Method (RGM), my model explicitly includes 12C+12C and alpha+20Ne reaction channels (with excited states). This approach provides a consistent, simultaneous, description of fusion, elastic scattering, and 24Mg spectroscopy. Results for 12C+12C elastic scattering show excellent agreement with experimental data, significantly improving the single-channel approximations. Spectroscopic analysis reveals that 24Mg states and resonances are highly mixed configurations, contradicting the concept of pure "molecular states." The calculated fusion S-factor is consistent with available experimental data and predicts both narrow and broad resonances near the Coulomb barrier. Main resonance widths originate primarily from the alpha+20Ne exit channels. The S-factor exhibits a decrease at low energies, providing a microscopic support for the hypothesis of fusion hindrance. This work is a first step towards a reliable theoretical extrapolation of the 12C+12C reaction to deep stellar burning temperatures. Future works should include the neutron and proton channels to provide a complete description of the 12C+12C fusion.
nucl-thnucl-exPRC(2026)·3 citations
08
The Delta-isobar masquerade: intrahadronic phase transitions and their quark-mimicking signatures in neutron stars
Martin O. Canullan-Pascual🇦🇷 · Germán Lugones🇧🇷 · Ignacio F. Ranea-Sandoval🇦🇷 · Milva G. Orsaria🇦🇷
We investigate the conditions under which $Δ (1232)$ isobars trigger a first-order phase transition within purely hadronic neutron-star matter, using the SW4L relativistic mean-field parametrization. For scalar-vector coupling differences $0.15 ≲ x_{σ Δ} - x_{ω Δ} ≲ 0.2$ and $x_{σ Δ} ≳ 1.3$ , the onset of $Δ^{-}$ resonances produces a van der Waals-like instability driven by a self-amplifying feedback in the scalar meson sector, in which the $Δ^{-}$ particle fraction acts as the order parameter of a Landau-type transition. A Maxwell construction yields a sharp density discontinuity at baryon densities $n_{b} \sim (1.3$ - $2) n_{0}$ , separating a $Δ$ -free outer core from a $Δ$ -rich inner core. The resulting neutron-star sequences satisfy all current multimessenger constraints: maximum masses $M_{max} \approx 2.15$ - $2.25 M_{⊙}$ , radii $R_{1.4} \approx 11$ - $12$ km, and tidal deformabilities $Λ_{1.4} \approx 190$ - $480$ , compatible with NICER observations and GW170817. We compute, for the first time for a $Δ$ -induced interface, the $ℓ = 2$ composition $g$ -mode eigenfrequencies, obtaining $ν_{g} \sim 400$ - $1100$ Hz with gravitational-wave damping times $τ_{g} \sim 1 0^{3}$ - $1 0^{9}$ s. These frequencies overlap quantitatively with those predicted for hadron-quark phase-transition interfaces, demonstrating that the mass-radius ``knee'', reduced tidal deformability, and $g$ -mode spectrum conventionally regarded as signatures of quark deconfinement can be reproduced by a purely intrahadronic mechanism. This extends the masquerade problem from static observables to the domain of gravitational-wave asteroseismology, implying that a future detection of a discontinuity $g$ -mode alone would not suffice to identify quark matter in neutron-star cores.
nucl-thastro-ph.HE1 citation
09
Nuclear binding, correlations, and the $A$ -dependence of the EMC effect
Omar Benhar🇮🇹 · Alessandro Lovato🇺🇸
The measurements of inclusive electron scattering from nuclear targets carried out at the Thomas Jefferson National Accelerator Facility in the mid 2000s have provided valuable novel information on the $A$ -dependence of the modifications of nuclear structure functions known as EMC effect. We argue that these data are best described in terms of the scaling variable $y$ , designed to take into account dynamical effects in interacting many-particle systems, and analyse the $A$ -dependence of the slope of the inclusive cross section ratios, $R_{A} = (σ_{A} / A) / (σ_{2} /2)$ , providing a measure of the size of the EMC effect in the region where nuclear binding plays a leading role. The results of our study clearly hint at a linear correlation between $d R_{A} (y) / d y$ and the average nucleon removal energy $⟨ E_{A} ⟩$ . The role of correlation effects in the determination of $⟨ E_{A} ⟩$ is highlighted.
nucl-th0 citations
10
Fluctuation-Dissipation Relation for Hard Partons in a Gluonic Plasma
Amit Kumar🇨🇦 · Abhijit Majumder🇺🇸 · Ismail Soudi🇩🇪 · Johannes Heinrich Weber🇩🇪
We derive a fluctuation dissipation relation connecting the drag and diffusion jet transport coefficients for an energetic light quark traversing a non-perturbative thermalized gluon plasma. The hard quark is taken to be close to on-shell, with an energy scale parametrically larger than the medium temperature. We introduce a general complex-valued function for each transport coefficient. Evaluating these in the deep Euclidean momentum region enables their expression in terms of local operators. Using contour-integration techniques, we relate these local operators, after vacuum subtraction, to the physical transport coefficients that arise along a branch cut, close to light-like dispersion. The derived relation relates the longitudinal drag coefficient to the longitudinal and transverse diffusion coefficients, and the thermal gluon condensate.
↳ hep-phhep-latnucl-th0 citations
11
Flavorful Lepton Number Violation at the EIC
Sebastián Urrutia Quiroga🇺🇸 · Vincenzo Cirigliano🇺🇸 · Wouter Dekens🇺🇸 · Kaori Fuyuto🇯🇵 · Emanuele Mereghetti🇺🇸
We explore the prospects of detecting flavorful lepton number violation at the Electron-Ion Collider (EIC) through resonant production of heavy neutral leptons (HNLs), resulting in $e^{-} p \to ℓ_{α}^{+} + k j + X$ , where $α \in {e, μ, τ}$ and $k$ denotes the number of jets. We work in the $ν$ SMEFT framework of the Standard Model Effective Field Theory augmented with $n$ singlet HNLs, one of which is in the mass range $10 - 100$ ~GeV, within kinematic reach of the EIC. To explore the EIC sensitivity, we focus on the HNL production mechanism induced by mixing with light neutrinos. We study kinematic distributions for signal and backgrounds, including hadronization and detector effects, and suggest a set of cuts to minimize backgrounds. In the mass range considered, we find that the EIC with muon detection capabilities and an integrated luminosity of $100 fb^{- 1}$ can reach sensitivities comparable to the strongest direct (LHC) and indirect constraints, and is especially relevant in the $ν$ SMEFT framework beyond dimension four. Our study motivates further assessment of muon detection capabilities at the EIC and $τ$ hadronic reconstruction, as well as a more general theoretical analysis involving production mechanisms mediated by higher-dimensional operators in the effective theory.
↳ hep-phhep-exnucl-exnucl-th1 citation
12
The 2027-2034 Vision for Nuclear Physics in Canada, with an outlook to 2041
Corina Andreoiu · Svetlana Barkanova · Gregory Christian · Alexandros Gezerlis · Garth Huber · Jeffery W. Martin · Ruben Sandapen
The Canadian subatomic physics community establishes its scientific, and thus funding, priorities through periodic Long-Range Plans (LRP). The community is now putting together a new LRP, which will be in effect from 2027 through 2034, with its scope extending through 2041. As part of this process, the Canadian Institute of Nuclear Physics (CINP) has put together a strategic report, following an extensive consultation process. The report describes the broad and ambitious research program undertaken by the Canadian nuclear physics research community, both onshore and abroad, touching on key questions regarding the origin, evolution, and structure of visible matter in the universe. This document provides a grid of different Canadian nuclear physics projects undertaken now and in the future, and their associated timelines. It concludes with specific recommendations for maximizing Canadian scientific output in nuclear physics.
↳ nucl-exastro-ph.SRhep-exnucl-th+11 citation
13
Confined and Deconfined Phases of Qubit Regularized Lattice Gauge Theories
Shailesh Chandrasekharan🇺🇸
We construct simple qubit-regularized Hamiltonian lattice gauge theories formulated in the monomer--dimer--tensor-network (MDTN) basis that are free of sign problems in the pure gauge sector. These models naturally realize both confined and deconfined phases. Using classical Monte Carlo methods, we investigate the associated finite-temperature phase transitions and show that they exhibit the expected universality classes of conventional SU(N) lattice gauge theories in various spacetime dimensions. Furthermore, we argue that second-order quantum phase transitions separating the confined and deconfined phases are likely to exist. Such critical points would provide a nonperturbative route to defining continuum limits of qubit-regularized gauge theories, potentially allowing Yang--Mills theory and related continuum gauge theories to emerge from finite-dimensional lattice constructions.
↳ hep-lathep-thnucl-th0 citations
14
Universality in spacetime $ω$ modes of quarkyonic stars
D. Dey🇮🇳 · Jeet Amrit Pattnaik🇮🇳 · R. N. Panda🇮🇳 · S. K. Patra🇮🇳
The gravitational wave $ω$ mode spectrum presents a unique window into the dense interior of neutron stars, probing physics inaccessible to electromagnetic observations. This work investigates the $ω$ modes of compact stars composed of quarkyonic matter. The quarkyonic model, which describes a cross-over transition between nucleonic and quark matter treated as quasi-particles, is formulated within the Relativistic Mean-Field (RMF) theory using the G3 and IOPB-I parameterizations. This core is surrounded by a mantle of hadronic matter, creating a multicomponent stellar interior. The overall Equation of State (EOS) is governed by two key parameters: the transition density ( $n_{t}$ ), the QCD confinement scale ( $Λ_{cs}$ ), which are varied to construct models consistent with current astrophysical constraints on mass and radius. We compute the complex eigenfrequencies (damped oscillations) of the fundamental and first excited $ω$ modes using the phase-amplitude method within a full general relativistic framework. Our simulations reveal that the admixed quarkyonic structure produces a unique $ω$ mode signature, distinctly different from pure hadronic or hybrid stars. The spectrum exhibits a strong, degenerate dependence on the EOS, where the stiffening effect of the quarkyonic matter influences oscillation frequencies and damping times in a characteristic manner. We also demonstrate that $ω$ mode frequencies for quarkyonic stars follow approximate universal relations, largely independent of the EOS.
↳ astro-ph.HEnucl-thPRD(2026)·0 citations
15
Form factors of the $ρ$ meson from effective field theory and the lattice
Ulf-G. Meißner🇩🇪 · Akaki Rusetsky🇩🇪 · Ajay S. Sakthivasan🇩🇪 · Gerrit Schierholz🇩🇪 · Jia-Jun Wu🇨🇳
The calculation of resonance form factors in effective field theory as well as on the lattice is a highly challenging task. In a recent paper, we proposed a novel method based on the introduction of a background field and the Feynman-Hellmann theorem to address the problem, and applied it to a toy model. In the present work we use this method for the electromagnetic form factors of the $ρ$ -meson. By matching the results to Chiral Perturbation Theory, we provide a first, crude estimate of all three form factors of the $ρ$ -meson within the effective field theory. Contact contributions to these form factors turn out to be substantial. A procedure for lattice calculations is outlined, paving the way for an ab initio approach to the problem.
↳ hep-lathep-phnucl-thJHEP(2026)·6 citations
16
Understanding the impact of nuclear effects on proton decay searches with the GiBUU model
Qiyu Yan🇨🇳 · Akira Takenaka · Kai Gallmeister🇩🇪 · Xianguo Lu🇬🇧 · Ulrich Mosel🇩🇪 · Yangheng Zheng🇨🇳
Proton decay searches in the next generation of water Cherenkov detectors, such as Hyper-Kamiokande, are expected to probe the $1 0^{35}$ -year lifetime regime where atmospheric neutrino backgrounds and systematic uncertainties begin to play an increasingly important role. In this study, we employ the GiBUU framework and reevaluate the proton decay search sensitivity for the $p \to e^{+} π^{0}$ channel by incorporating a typical event reconstruction performance in water Cherenkov detectors. Using sophisticated models implemented in GiBUU -- most notably the mean-field potential and Boltzmann transport -- which have been benchmarked against accelerator neutrino scattering data, in particular pion production, we find that the resulting proton decay signal detection efficiency and atmospheric neutrino background rate are comparable to those previously evaluated for the current and near future water Cherenkov experiments using $ad hoc$ nuclear models. In addition to pion final-state interactions, we evaluate the impact of differences in the Fermi momentum distribution of nucleons in the nucleus, as a source of systematic uncertainty, on the signal detection efficiency and the expected background event rate. We find that the uncertainty associated with pion final-state interactions is moderate, whereas the choice of Fermi momentum distribution can significantly affect the estimated atmospheric neutrino background rate and constitutes the dominant contribution. Our study provides an independent and complementary characterisation of nuclear effects on proton decay searches and helps to refine sensitivity estimates in the regime where systematic uncertainties become more relevant.
↳ hep-exnucl-exnucl-thPRD(2026)·1 citation
17
Universal and non-universal finite-volume effects in the vicinity of chiral phase transition in (2+1)-flavor QCD
Sabarnya Mitra🇩🇪 · Jishnu Goswami🇩🇪 · Frithjof Karsch🇩🇪
In this proceeding, we discuss the finite-size scaling analysis of the order parameter related to the chiral phase transition in QCD with two massless quarks. We use data obtained in lattice QCD calculations performed with highly improved staggered quarks (HISQ) for a range of light quark masses, $1/240 \leq m_{ℓ} / m_{s} \leq 1/27$ for different spatial volumes ( $N_{σ}$ ) on Euclidean lattices with temporal extent $N_{τ} = 8$ , satisfying $3 N_{τ} \leq N_{σ} \leq 10 N_{τ}$ . We observe that infinite volume extrapolated data for the order parameter agree reasonably well with the expected $O (2)$ scaling behavior even for physical ratios of the light-to-strange quark mass ratio. We quantify deviations from asymptotic scaling and perform a detailed analysis of the influence of finite-size effects in terms of temperature and quark masses at a fixed lattice cutoff. This is crucial for improving the reliability of the infinite-volume extrapolated estimate of the chiral order parameter and for a more precise determination of chiral phase transition temperature from direct Lattice QCD simulations.
↳ hep-lathep-phhep-thnucl-ex+12 citations

Affiliations

first authorsco-authorsvia INSPIRE