Nuclear Theory·nucl-th

Friday·February 20, 2026

8 papers—4 primary·4 cross-listed

01
From $χ$ EFT to Multi-Region Modeling: Neutron star structure with a polytropic extension of $χ$ EFT and MUSES Calculation Engine multi-layer modeling
Federico Nola
Neutron stars provide a unique environment to probe the properties of dense nuclear matter. In this work, we present a comparative study between two approaches to modeling the neutron star structure: a Chiral Effective Field Theory based approach and the MUSES Calculation Engine framework, which uses three different approaches for the three density regions. We analyze the resulting mass-radius relations, discussing the respective advantages and limitations of the two methods.
nucl-thastro-ph.HE0 citations
02
Spectra and elliptic flow of light hadrons in an expanding fire-cylinder model for the RHIC Beam Energy Scan
Anand Rai🇮🇳 · Ashutosh Dwibedi🇮🇳 · Sabyasachi Ghosh🇮🇳
We investigate the transverse momentum spectra ( $p_{T}$ ) and elliptic flow ( $v_{2}$ ) of $π^{\pm}$ , $K^{\pm}$ , $p$ , and $p ˉ$ produced in peripheral Au+Au collisions at $s_{NN} = 7.7$ , 11.5, 19.6, 27, and 39 GeV in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). The analysis is carried out within an expanding elliptic fire-cylinder model that incorporates longitudinal expansion and anisotropic transverse flow. Particle production at kinetic freeze-out is obtained using a local equilibrium distribution function with a blast-wave-like fluid velocity profile derived from the expansion dynamics of the elliptic fire-cylinder. The model parameters governing the collective expansion are first constrained by fitting the midrapidity $p_{T}$ spectra of $π^{\pm}$ and are then applied, without further adjustment, to $K^{\pm}$ , $p$ , and $p ˉ$ . The model provides a consistent description of the $p_{T}$ spectra and reproduces the qualitative behavior of the elliptic flow for all considered particle species.
nucl-thhep-phNPA(2026)·1 citation
03
Model bias and parameter optimisation with the example of INCL/ABLA
Jason Hirtz🇫🇷 · Jean-Christophe David🇫🇷 · Ingo Leya🇨🇭 · José Luís Rodríguez Sánchez🇪🇸 · Georg Schnabel🇦🇹
The accuracy and precision of high-energy spallation models play a crucial role in the design and development of new applications and experiments, as well as in data analysis. We discuss the complementarity between parameter optimisation and model bias estimation approaches within a Bayesian framework. This is illustrated using the IntraNuclear Cascade model of Liège (INCL) together with the Ablation model (ABLA), for which these two approaches for model bias estimation have been applied independently in previous works.
nucl-thEPJA(2026)·0 citations
04
Evidence for Multimodal Superfluidity of Neutrons
Yuan-Zhuo Ma · Georgios Palkanoglou · Joseph Carlson · Stefano Gandolfi · Alexandros Gezerlis · Gabriel Given · Ashe Hicks · Dean Lee · Kevin E. Schmidt · Jiabin Yu
We present theoretical and experimental evidence for a new phase of matter in neutron-rich systems that we call multimodal superfluidity. Using ab initio lattice calculations, we show that the condensate consists of coexisting s-wave pairs, p-wave pairs in entangled double pair combinations, and quartets composed of bound states of two s-wave pairs. We identify multimodal superfluidity as a general feature of single-flavor spin-1/2 fermionic systems with attractive s-wave and p-wave interactions, provided the system is stable against collapse into a dense droplet. Beyond neutrons at sub-saturation densities, we demonstrate that this phase appears in generalized attractive extended Hubbard models in one, two, and three dimensions. We elucidate the mechanism for this coexistence using self-consistent few-body Cooper models and compare with Bardeen-Cooper-Schrieffer theory. We also derive the form of the effective action and show that spin, rotational, and parity symmetries remain unbroken. Finally, we analyze experimental data to show that p-wave pair gaps and quartet gaps are present in atomic nuclei, and we discuss the consequences of this new phase for the structure and dynamics of neutron star crusts.
nucl-thastro-ph.SRcond-mat.supr-connucl-ex+14 citations
05
Quarkonium in non-zero isospin chemical potential environment at $T ≃ 0$
Seyong Kim🇰🇷 · Bastian B. Brandt🇩🇪 · Gergely Endrődi🇭🇺
We study how the isospin asymmetry affects quarkonium states in QCD at near zero temperature. Using lattice Non-Relativistic QCD formalism, we calculate bottom quark correlators in the gauge field ensembles generated with $N_{f} = 2 + 1$ flavors of dynamical staggered quarks whose dynamics include the isospin chemical potential effect and then construct $S -$ and $P -$ wave quarkonium state correlators. From these quarkonium correlators, we consider the ratios of quarkonium correlators at non-zero isospin chemical potential to that at $μ_{I} a = 0.000$ . Here, the gauge field ensemble with $μ_{I} a = 0.000, 0.048, 0.053, 0.059, 0.066, 0.080, 0.092$ and $0.106$ on a $3 2^{3} \times 48$ lattice with non-zero isospin current strength $λa = 0.0010, 0.0018,$ and $0.0036$ , where $m_{π} = 135$ MeV and $a = 0.1535$ fm from \cite{Brandt:2022hwy}, are used. Preliminary results suggest that for $μ_{I} a = 0.106$ , the Upsilon mass gets heavier than the Upsilon mass in the vacuum and that below $μ_{I} a = 0.106$ the isospin asymmetry effect on the Upsilon mass is not monotonic.
↳ hep-latnucl-th0 citations
06
Hartree shift and pairing gap in ultracold Fermi gases in the framework of low-momentum interactions
Michael Urban🇫🇷 · S. Ramanan🇮🇳
In this paper we consider a two-component gas of fermions on the BCS side of the BCS-BEC crossover at zero temperature. We use a momentum dependent interaction that reproduces the s-wave scattering phase shifts of a contact interaction up to a momentum cutoff that is scaled with the Fermi momentum. Using a diagrammatic formulation of Bogoliubov many-body perturbation theory, suitably augmented by self-consistency conditions, we obtain the Hartree shift and the pairing gap to third order. In the weak-coupling regime, our results are not only well-converged but also agree with the well-established Gor'kov-Melik-Barkhudarov corrections for the gap and the Galitskii result for the Hartree shift. Near the unitary regime, our results for the Nambu-Gor'kov self-energy are less converged, but there is still reasonable agreement with experiments as well as with quantum Monte-Carlo results. Perspectives for improvements and applications of this approach to neutron matter are discussed.
↳ cond-mat.quant-gasnucl-thPRA(2026)·1 citation
07
Chiral symmetry restoration effects onto the meson spectrum from a Dyson-Schwinger and Bethe-Salpeter approach
Reinhard Alkofer🇦🇹 · Christian S. Fischer🇩🇪 · Fabian Zierler🇩🇪
Light meson spectra are studied in a Dyson-Schwinger/Bethe-Salpeter approach to QCD. By varying the interaction strength of three sets of models for the quark-antiquark interaction, the transition from the chiral symmetric to the chirally broken regime in the vacuum is studied. The simplest type of these models leads to degenerate meson spectra for a large domain of the strength parameter. The more sophisticated and thus more realistic models show significantly smaller parameter domains for which degenerate meson spectra are obtained. The underlying mechanism for obtaining and then lifting degeneracies is traced back to the location of the quark propagators' poles, in particular, whether they are beyond or within the domain of integration in the Bethe-Salpeter equation. In view of this mechanism the potential relation of the obtained degeneracies to the dynamical emergence of symmetries is discussed, adding thereby another point of view on the conjectured chiral spin symmetry of QCD in the temperature domain right above the crossover.
↳ hep-phnucl-thPRD(2026)·5 citations
08
Hyperon longitudinal polarization and vector meson spin alignment in a thermal model for heavy-ion collisions
Soham Banerjee🇮🇳 · Samapan Bhadury🇮🇳 · Wojciech Florkowski🇵🇱 · Amaresh Jaiswal🇮🇳 · Radoslaw Ryblewski🇵🇱
The concept of a common local spin equilibrium for both spin-1/2 and spin-1 particles is incorporated into a thermal model of particle production in heavy-ion collisions at the top RHIC energies. We show that an effective spin polarization tensor leading to a correct description of the longitudinal spin polarization of $Λ$ hyperons simultaneously yields a positive alignment of vector mesons ( $ϕ$ and $K^{* 0}$ ) that grows monotonically with transverse momentum and centrality. Similar trends can be seen in the data, suggesting a possible common mechanism for longitudinal spin polarization and alignment. However, model calculations are insufficient to explain the data in a fully quantitative way. The correlation found between the magnitude of the $Λ$ longitudinal polarization and vector meson alignment suggests further more elaborate investigations of this issue.
↳ hep-phhep-thnucl-thActa Phys.Polon.B(2026)·1 citation

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