Nuclear Theory·nucl-th

Tuesday·December 9, 2025

17 papers—9 primary·8 cross-listed

10
[Submitted on 26 Nov 2025] (cross-list from hep-lat)
The phases of QCD reached in terrestrial and cosmic colliders
Sourendu Gupta🇮🇳
We review the current state of knowledge of the phase diagram of QCD through lattice, effective field theories, and chiral models. Several sections through the three dimensional phase diagram are known for $N_{f} = 2 + 1$ with good precision. Due to technical advances in lattice techniques over the last decade or so, new aspects of the phase diagram can now be explored. We review current lattice results. The newly acquired knowledge can be used to reconstruct the full phase diagram for physical QCD, \ie, $N_{f} = 1 + 1 + 1$ . We remark on the computations which would help understand this better, and what the current constraints are on matter in neutron star cores. We also remark on the physics of the chiral transition and neutron stars in the 't Hooft large $N_{c}$ limit.
Comments:
Small changes between v1 and published version (v2)
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2511.21108 [pdf]
0 citations
11
[Submitted on 5 Dec 2025] (cross-list from hep-ph)
Inferring the breakdown scales of the chiral expansions for $g_{A}$ and $m_{N}$
Andreas Ekström🇸🇪 · Daniel R. Phillips🇺🇸 · Lucas Platter🇺🇸 · Matthias R. Schindler🇺🇸
We apply Bayesian inference to the order-by-order chiral perturbation theory ( $χ$ PT) expansions for the axial-vector coupling constant $g_{A}$ and the nucleon mass m_N, and thereby infer the scales at which $χ$ PT breaks down for these two observables. Using a pointwise Bayesian analysis, we find that the inferred breakdown scales are notably different for the two observables. For the chiral expansion of $g_{A}$ , we obtain $25 1_{- 50}^{+ 20}$ MeV and $21 1_{- 30}^{+ 20}$ MeV using two distinct sets of low-energy constants, while for the chiral expansion of $m_{N}$ we infer a significantly larger breakdown scale of $49 1_{- 90}^{+ 60}$ MeV.
Comments:
7 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2512.06088 [pdf]
PLB(2026)·3 citations
12
[Submitted on 5 Dec 2025] (cross-list from hep-ph)
Photon emission from weakly magnetized neutral pions
Xinyang Wang🇨🇳 · Fan Lin🇨🇳 · Igor Shovkovy🇺🇸
Using a hadronic framework, we derive an explicit expression for photon production from neutral pions in a weak background magnetic field. Our calculation is built on the proton triangle diagram with an effective Yukawa $π^{0}$ -proton coupling, offering an alternative to quark-level descriptions that is advantageous when the magnetic length greatly exceeds the proton size. Corrections to the pion decay constant are computed up to second order in the magnetic-field strength, revealing that the field generally suppresses the decay rate. Quantitatively, however, the effect remains modest even for fields as strong as $∣ e B ∣ ≃ m_{π}^{2}$ . The differential photon emission rate exhibits anisotropy, with the strongest suppression occurring when the pion momentum is perpendicular to the magnetic field. Overall, the modification of the $π^{0} \to γ γ$ rate is parametrically small, scaling as $∣ e B ∣^{2} / m_{P}^{4}$ , where $m_{P}$ is the proton mass. While the magnetic-field-induced anisotropy is conceptually interesting in principle, it is likely too small to be resolved in present heavy-ion measurements.
Comments:
21 pages, 3 figures; v2: final version accepted for publication in Physical Review D, with several expanded discussions
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2512.06090 [pdf]
PRD(2026)·1 citation
13
[Submitted on 6 Dec 2025] (cross-list from hep-th)
Maximally Symmetric Boost-Invariant Solutions of the Boltzmann Equation in Foliated Geometries
Mauricio Martinez🇺🇸 · Christopher Plumberg🇺🇸
In this work we study the relativistic kinetic theory of a boost-invariant conformal gas on a static, maximally symmetric background $d S_{3} \times R$ , considering all constant-curvature slicings of $d S_{3}$ - flat, spherical, or hyperbolic- and their associated symmetry groups. Using a symmetry-driven cotangent-bundle approach, we show that the isometry group of each slicing acts on phase space in such a way that only its Casimir invariants and the time-like coordinate unconstrained, so the distribution function depends solely on these quantities. This yields a unified boost-invariant exact solution of the Boltzmann equation valid for each constant-curvature foliation of $d S_{3} \times R$ . Specializing this general solution to the flat and spherical foliations reproduces the Bjorken and Gubser flows, respectively, while its restriction to the hyperbolic foliation produces a genuinely new analytic solution (`Grozdanov flow'). Hydrodynamics and free streaming emerge naturally as limiting regimes of this novel exact solution. We further comment on several relevant aspects of the new boost-invariant solution on the hyperbolic slicing and on their interpretation once mapped back to Minkowski space.
Comments:
v2: 27 pages + appendices, 2 figures. Expanded symmetry-reduction discussion in Sects. 2 and 3, including theorem/proposition statements and a complete new appendix; conclusions unchanged
Subjects:
High Energy Physics — Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2512.06257 [pdf]
PRD(2026)·2 citations
14
[Submitted on 6 Dec 2025] (cross-list from nucl-ex)
Identified charged hadron production in Au+Au collisions at $s_{NN}$ = 54.4 GeV with the STAR detector
STAR Collaboration: B. E. Aboona🇺🇸 · J. Adam🇨🇿 · G. Agakishiev🇷🇺 · I. Aggarwal🇮🇳 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · A. Aitbayev🇷🇺 · I. Alekseev🇷🇺 · E. Alpatov🇷🇺 · A. K. Alshammri🇺🇸 · A. Aparin🇷🇺 · S. Aslam🇨🇳 and 375 other authors
We present results on the production of $π^{\pm}$ , $K^{\pm}$ , $p$ , and $p ˉ$ in Au+Au collisions at $s_{NN}$ = 54.4~GeV using the STAR detector at RHIC, at midrapidity ( $∣ y ∣ <$ 0.1). Invariant yields of these particles as a function of transverse momentum are shown. We determine bulk properties such as integrated particle yields ( $d N / d y$ ), mean transverse momentum ( $⟨ p_{T} ⟩$ ), particle ratios, which provide insight into the particle production mechanisms. Additionally, the kinetic freezeout parameters ( $T_{kin}$ and $⟨ β_{T} ⟩$ ), which provide information about the dynamics of the system at the time of freezeout, are obtained. The Bjorken energy density ( $ϵ_{BJ}$ ), which gives an estimate of the energy density in the central rapidity region of the collision zone at the formation time $τ$ , is calculated and presented as a function of multiplicity for various energies. The results are compared with those from the models such as A Multi-Phase Transport (AMPT) and Heavy Ion Jet INteraction Generator (HIJING) for further insights.
Comments:
14 pages, 16 figures
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2512.06415 [pdf]
PRC(2026)·2 citations
15
[Submitted on 7 Dec 2025] (cross-list from hep-ph)
Nucleon 3D intrinsic spin structure from the weak-neutral axial-vector form factors
Yi Chen
Relativistic 3D weak-neutral axial-vector four-current and spin distributions inside a nucleon (or a general spin- $\frac{1}{2}$ hadron) including three weak-neutral axial-vector form factors are investigated for the first time. We clarify that the relativistic 3D axial charge distribution in the Breit frame is completely described by the induced pseudotensor form factor $G_{T}^{Z} (Q^{2})$ rather than by the axial form factor $G_{A}^{Z} (Q^{2})$ . We demonstrate that $R_{A} \equiv \frac{- 6}{G _{A}^{Z} ( 0 )} \frac{d G _{A}^{Z} ( Q ^{2} )}{d Q ^{2}}_{Q^{2} = 0}$ can not be interpreted as the physically meaningful 3D root-mean-square axial radius of a spin- $\frac{1}{2}$ hadron. The genuine axial radius for any spin- $\frac{1}{2}$ hadron in fact does not exist. We also show that the relativistic 3D weak-neutral spin radius $r_{spin} = ⟨ r_{spin}^{2} ⟩$ , with $⟨ r_{spin}^{2} ⟩ \equiv R_{A}^{2} + \frac{1}{4 M ^{2}} [1 + \frac{2 G _{P}^{Z} ( 0 )}{G _{A}^{Z} ( 0 )}]$ based on the relativistic and intrinsic 3D weak-neutral spin distribution in the Breit frame, is a physically meaningful radius that can be unambiguously defined for the nucleon, which provides an additional key motivation for the further determination of the induced pseudoscalar form factor $G_{P}^{Z} (Q^{2})$ . Numerically, we find that $R_{A} \approx 0.6510 fm$ , $r_{spin} \approx 2.1054 fm$ and $r_{spin} \equiv r_{spin} /3 \approx 0.7018 fm$ . For future experimental measurements of $G_{A}^{Z} (Q^{2})$ and $G_{T}^{Z} (Q^{2})$ , we also derive the full tree-level unpolarized differential cross sections for neutrino-proton and antineutrino-proton elastic scattering in the lab frame, in hoping to provide a complementary and new perspective to unveil the nucleon spin structure by using (anti)neutrino-based facilities.
Comments:
6 pages, 1 figure; to appear in PoS(SPIN2025)099; DOI: https://doi.org/10.22323/1.517.0099
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2512.06801 [pdf]
1 citation
16
[Submitted on 8 Dec 2025] (cross-list from hep-ph)
Chiral, parity-doublet, effective-Lagrangian mean-field theories for nuclear and astrophysical phenomenology
Ayon Mukherjee🇮🇳
Chiral-parity (parity-doublet) effective Lagrangian models provide a compact and symmetry-consistent framework for describing baryons and their negative-parity partners in terms of linearly-realized chiral symmetry. Unlike the conventional, linear, sigma model; the parity-doublet approach accommodates a chirally-invariant mass term, $m_{0}$ , allowing finite baryon-masses even when the chiral condensate melts. This feature enables a unified treatment of hadronic matter across vacuum, nuclear and dense astrophysical regimes. This compact review summarizes the key structures of parity-doublet Lagrangians; outlines the mean-field formulation for nuclear and stellar matter; and highlights recent phenomenological and lattice constraints on the chirally-invariant mass. Emphasis is placed on mirror versus naïve chiral assignments; the role of vector interactions in achieving nuclear saturation; and the implications of parity doubling for the equation-of-state of dense matter and neutron-star cooling. The review concludes with current theoretical challenges and perspectives for extending these models beyond the mean-field approximation.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2512.07172 [pdf]
Int.J.Mod.Phys.A(2026)·0 citations
17
[Submitted on 8 Dec 2025] (cross-list from hep-ph)
Chiral transition in a Non-Abelian Quasi-Particle Model with three quark flavours
Eleftherios P. Politis🇬🇷 · Antonis Tsapalis🇬🇷 · Fotios K. Diakonos🇬🇷
We combine the recently introduced Non-Abelian Quasi-Particle Model (NAQPM) for gluons with an ideal Fermi gas of three quark species with the aim to describe the equation of state (energy density vs. temperature) of $2 + 1$ - flavour Lattice-QCD at zero chemical potential. Allowing temperature dependent masses for the fermions, we show that above a critical temperature $T_{c}$ the quark mass has to drop rapidly in order to obtain energy density values compatible with the Lattice-QCD results. Within this framework, thus, the restoration of chiral symmetry in the system is observed. Furthermore, we demonstrate that the gluon variance -- which is a fundamental quantity of the NAQPM -- is strongly correlated to the fermion mass and decreases by orders of magnitude through the transition. The high temperature phenomenological characteristics of the gluon appear consistent to properties of the perturbative QCD gluon. The model indicates that color deconfinement and chiral symmetry restoration are interrelated and classical configurations of the QCD dynamics play an important role to the criticality of the system.
Comments:
10 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2512.07633 [pdf]
PLB(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE