Nuclear Theory·nucl-th

Monday·April 14, 2025

7 papers—3 primary·4 cross-listed

04
Kaon and Pion Fragmentation Functions
Hui-Yu Xing🇨🇳 · Wen-Hao Bian🇨🇳 · Zhu-Fang Cui🇨🇳 · Craig D. Roberts🇨🇳
The Drell-Levy-Yan relation is employed to obtain pion and kaon elementary fragmentation functions (EFFs) from the hadron-scale parton distribution functions (DFs) of these mesons. Two different DF sets are used: that calculated using a symmetry-preserving treatment of a vector $\times$ vector contact interaction (SCI) and the other expressing results obtained using continuum Schwinger function methods (CSMs). Thus determined, the EFFs serve as driving terms in a coupled set of hadron cascade equations, whose solution yields the complete array of hadron-scale fragmentation functions (FFs) for pion and kaon production in high energy reactions. After evolution to scales typical of experiments, the SCI and CSM FF predictions are seen to be in semiquantitative agreement. Importantly, they conform with a range of physical expectations for FF behaviour on the endpoint domains $z ≃ 0, 1$ , e.g., nonsinglet FFs vanish at $z = 0$ and singlet FFs diverge faster than $1/ z$ . Predictions for hadron multiplicities in jets are also delivered. They reveal SU $(3)$ symmetry breaking in the charged-kaon/neutral-kaon multiplicity ratio, whose size diminishes with increasing reaction energy, and show that, with increasing energy, the pion/kaon ratio in $e^{+} e^{-} \to h X$ diminishes to a value that is independent of hadron masses.
↳ hep-phhep-exhep-latnucl-ex+1EPJC(2025)·18 citations
05
Phase Boundary of Nuclear Matter in Magnetic Field
Yuki Amari🇯🇵 · Muneto Nitta🇯🇵 · Zebin Qiu🇯🇵
Nuclear matter with a strong magnetic field is prevalent inside neutron stars and heavy-ion collisions. In a sufficiently large magnetic field the ground state is either a chiral soliton lattice (CSL), an array of solitons of the neutral pion field, or a domain-wall Skyrmion phase in which Skyrmions emerge inside the chiral solitons. In the region of large chemical potential and a magnetic field lower than its critical value for CSL, a Skyrmion crystal is expected to take up the ground state based on the chiral perturbation theory at the next leading order. We determine the phase boundary between such a Skyrmion crystal and the QCD vacuum. There was a conjecture that a magnetic field deforms the Skyrmion into a pancake shape whose boundary is a superconducting ring of charged pions. In contrast, through the exact Skyrmion solution, we find that the pancake conjecture holds approximately in a strong magnetic field, but fails for a weak one. We also validate that a Skyrmion would shrink to null without the Skyrme term, although Derrick's scaling law is modified by a background magnetic field, and the stability at the leading order is not ruled out in theory.
↳ hep-phnucl-thJHEP(2025)·12 citations
06
Dependence of postmerger properties on the thermal heating efficiency in neutron star mergers
Ming-Zhe Han🇩🇪 · Yong Gao🇩🇪 · Kenta Kiuchi🇩🇪 · Masaru Shibata🇩🇪
We systematically perform numerical-relativity simulations for equal-mass binary neutron star mergers for the models varying the thermal index $Γ_{th}$ with three different equations of state (EOSs) of the neutron stars (NSs), which are consistent with current multimessenger observational data and state-of-the-art theoretical calculations, and two different binary total mass ( $m_{0} = 2.7 and 2.9 M_{⊙}$ ). By varying the value of $Γ_{th}$ within the hybrid EOS framework, we investigate the thermal effects on the merger dynamics, gravitational waves (GWs), and the dynamical mass ejection process. We find that the choice of the constant $Γ_{th}$ can change the outcome of the remnant for specific EOSs and $m_{0}$ . We also show that the dynamical ejecta mass is affected by the $Γ_{th}$ value in a different way for different EOSs: for a stiff EOS the ejecta mass is high when $Γ_{th}$ is small, while for softer EOSs the largest ejecta is achieved when $Γ_{th} = 1.3$ -- $1.4$ . While the inspiral motion does not depend on the $Γ_{th}$ value, the postmerger phase evolution is highly affected by that. We show that the dominant peak frequency $f_{2}$ of the postmerger GW spectrum monotonically decreases as the $Γ_{th}$ increases. We find that the universal relations between NS macroscopic properties and postmerger GW frequencies are subject to non-negligible thermal uncertainties, which can obscure the universal relation between the tidal deformability and $f_{2}$ .
↳ astro-ph.HEgr-qcnucl-thPRD(2025)·6 citations
07
Hidden Twin Star Solutions from an Agnostic Speed-of-Sound Model: Confronting XTE J1814--338's Extreme Compactness
Tianzhe Zhou · Chun Huang
The twin star configuration, where two neutron stars share the same mass but exhibit different radii, arises from a strong first-order phase transition within the stellar interior. In widely used equation of state (EoS) meta-models, such as the Polytrope (PP) and Speed-of-Sound (CS) models, this first-order phase transition behavior can be naturally mimicked by tuning some model parameters. Here, we systematically explore the under-explored parameter space within one of a widely adopted CS model that leads to twin stars via a strong first-order phase transition. Within this twin-star subspace, we perform a comprehensive Bayesian analysis that integrates mass--radius (MR) constraints from X-ray observations of rotation-powered millisecond pulsars. The resultant twin star branch, situated within the 1--1.2 $M_{⊙}$ mass range and approximately 7 km in radius, surprisingly coincides with the MR ranges proposed for the recent anomaly in the Accreting Millisecond X-ray Pulsars XTE J1814--338 (J1814), suggesting a hybrid twin star configuration. Moreover, incorporating the J1814 observation as an additional constraint yields an extreme phase transition pressure $P_{trans} = 108. 9_{- 4.85}^{+ 6.46}$ MeV/fm $^{3}$ , a transition density of $ε_{trans} / ε_{0} = 4.84 7_{- 0.134}^{+ 0.271}$ (where $ε_{0}$ is the nuclear saturation energy density) and an energy density jump $Δ ε = 558. 7_{- 278.7}^{+ 303.6}$ MeV/fm $^{3}$ , corresponding to $Δ ε / ε_{0} = 3.71 6_{- 1.854}^{+ 2.020}$ . Notably, to satisfy all astrophysical constraints, the speed of sound inside of the hybrid twin star core is driven toward the speed of light ( $c_{s}^{2} / c^{2} > 0.9$ ), indicating the potential presence of strongly interacting, exotic matter in this core region.
↳ astro-ph.HEgr-qcnucl-th13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Kaon and Pion Fragmentation Functions

Phase Boundary of Nuclear Matter in Magnetic Field

Dependence of postmerger properties on the thermal heating efficiency in neutron star mergers

Hidden Twin Star Solutions from an Agnostic Speed-of-Sound Model: Confronting XTE J1814--338's Extreme Compactness

Affiliations