Nuclear Theory·nucl-th

Tuesday·February 24, 2026

16 papers—9 primary·7 cross-listed

10
[Submitted on 20 Feb 2026] (cross-list from cond-mat.str-el)
Analytic continuation of Green's functions with a neural network
Fakher Assaad · Johanna Erdmenger · Anika Götz · René Meyer · Martin Rackl · Yanick Thurn
An important problem in many-body physics is to reconstruct the spectral density from the imaginary-time domain Green's function. Typically, the imaginary-time Green's function is generated by Monte Carlo methods. As the one-point fermionic kernel diverges exponentially for large frequencies, numerical noise generically causes instabilities. We use a convolutional neural network to obtain the spectral density for a given imaginary time Green's function. The network is trained by data which we generate using random Gaussians. We improve the training data set available by including collision centers for the Gaussians rather than employing uniformly distributed Gaussians. Our network is constructed in such a way that its output fulfills positive semidefiniteness. We compare the results of our network with results of the Maximum Entropy method (MaxEnt), a standard method for the same reconstruction problem for the spectral density. This comparison is performed for three different cases, namely our Gaussian based test data as well as two physical models, the 1d Hubbard model showing spin-charge separation, and the two-dimensional SSH model in the self-consistent Born approximation. We find that the network outperforms MaxEnt when presented data close to the training set. For the physical models considered, MaxEnt recognizes physical features more precisely as compared to our network prediction. While it is hard to improve MaxEnt, the quality of the network depends on the training data set which can be systematically enhanced and improved.
Comments:
15 pages, 4 figures, 1 table
Subjects:
Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2602.18561 [pdf]
0 citations
11
[Submitted on 22 Feb 2026] (cross-list from astro-ph.HE)
Evidence of Nuclear Urca Process in the Ocean of Neutron-Star Superburst MAXI J1752 $-$ 457
Hao Huang · Akira Dohi · Amira Aoyama · Tomoshi Takeda · Nobuya Nishimura
We propose that the rapid cooling of the neutron star following its X-ray superburst in MAXI J1752 $-$ 457 over a period of 4 days, observed by two Japanese satellites, MAXI and NinjaSat, is due to enhanced neutrino emission from cycles of electron capture and $β^{-}$ decay involving odd- $A$ nuclei (or Urca pairs) in the ocean. Hence, this work provides the first indication of the possible existence of such a ``nuclear Urca process". The observation of MAXI J1752 $-$ 457 implies a hot ignition layer with a maximum temperature of $\sim 4 GK$ , located near the Urca shell in the ocean, such that the nuclear Urca process becomes dominant for up to $\sim 2$ days after the superburst. This behavior is distinct from that of normal Type-I X-ray bursts, which are triggered by hydrogen or helium burning in much shallower layers than those of superbursts. Our findings enable probing of superburst ashes through Urca pairs via long-term monitoring of crust cooling on day-long timescales.
Comments:
6 pages, 4 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2602.19018 [pdf]
1 citation
12
[Submitted on 22 Feb 2026] (cross-list from hep-ph)
Two nearby states in the $X (3872)$ region: Resolving the radiative-decay ratio tension with $η_{c 2}$
Satoshi X. Nakamura (Shandong University)🇨🇳
Recently, LHCb reported the radiative-decay ratio $R^{ψ γ} \equiv B [X (3872) \to ψ^{'} γ] / B [X (3872) \to J / ψ γ] = 1.67 \pm 0.25$ extracted from $B^{+} \to K^{+} (J / ψ γ, ψ^{'} γ)$ . This result differs markedly ( $\sim 4.6 σ$ ) from the BESIII value obtained from $e^{+} e^{-} \to γ (J / ψ γ, ψ^{'} γ)$ , $R^{ψ γ} = - 0.04 \pm 0.28$ . Such a significant tension suggests that more than one state in the $X (3872)$ region contributes to the processes. We therefore propose a two-state scenario: a shallow $D^{* 0} D ˉ^{0}$ bound state with $J^{P C} = 1^{++}$ and a $2^{-+}$ charmonium candidate, $η_{c 2}$ , slightly above the $D^{* 0} D ˉ^{0}$ threshold. We show that this hypothesis consistently describes these ratios along with other branching fractions and lineshapes across multiple processes. By contrast, fits without the $η_{c 2}$ component fail to reproduce the radiative-ratio data. We also predict helicity-angle distributions that motivates the future experiments to test the two-state hypothesis and search for the so-far missing $η_{c 2}$ .
Comments:
15 pages, 6 figures, 8 tables, figures added, published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2602.19165 [pdf]
PRD(2026)·2 citations
13
[Submitted on 23 Feb 2026] (cross-list from hep-ph)
Three-body molecular states composed of $D^{(*)}$ and two nucleons
Si-Yi Chen🇨🇳 · Fei-Yu Chen🇨🇳 · Xu-Liang Chen🇨🇳 · Lu Meng🇨🇳 · Ning Li🇨🇳 · Wei Chen🇨🇳
We study the three-body systems $D N N$ and $D^{*} N N$ within a hadronic molecular framework by combining a realistic nucleon-nucleon interaction with a $D^{(*)} N$ potential constrained by heavy-quark symmetry. The three-body Schrödinger equation is solved with the Gaussian Expansion Method, and the analytic structure of the spectrum is investigated using the Complex Scaling Method. We find that the $D N N$ system supports a robust and compact bound state in the $I (J^{P}) = \frac{1}{2} (1^{-})$ channel over a broad range of cutoff values, even when the corresponding $D N$ subsystem is weakly bound or unbound. For $D^{*} N N$ , the spin- $1$ nature of the heavy meson and the associated spin-dependent forces generate a clear spin hierarchy: deeply bound states appear in both $0^{-}$ and $2^{-}$ channels, while the $1^{-}$ channel exhibits a characteristic two-branch pattern with a strongly bound compact branch and a more weakly bound, spatially extended branch. The root-mean-square radii indicate pronounced spatial compression compared with the deuteron scale, highlighting the cooperative roles of realistic $N N$ correlations, the $D^{(*)} N$ interactions, and heavy-quark symmetry in forming compact heavy-flavor few-body bound states. No three-body resonances under complex scaling are found in the explored parameter space. Our results provide quantitative benchmarks for future experimental searches for such charmed-meson-nuclear bound states.
Comments:
14 pages, 7 figures, 4 tables, accepted for publication in Physical Review D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2602.19504 [pdf]
PRD(2026)·1 citation
14
[Submitted on 23 Feb 2026] (cross-list from hep-ph)
2025 EIC-France Workshop: Physics Highlights and Perspectives
F. Arleo · V. Bertone · J. Bettane · B. Blossier · F. Bock · F. Bossù · R. Boussarie · F. Bouyjou · O. Brand-Foissac · N. L. Bucuru Rodriguez · V. Calvelli · P. Caucal and 66 other authors
This document presents a synthesis of the theory contributions and discussions from the 2nd EIC-France Workshop, held at IJCLab (Orsay) on 1-3 December 2025. The workshop brought together members of the French hadron-physics community to review recent theoretical developments relevant to the future Electron-Ion Collider (EIC) and to coordinate national efforts in preparation for its early physics program. The report first summarizes the collider's initial running conditions and luminosity performance, as outlined in the EIC Early Science Matrix. It then provides concise overviews of the theoretical presentations on inclusive, semi-inclusive, exclusive, heavy-flavor, and small-x physics. Based on these discussions, two measurements emerged as especially well suited for early EIC operation and strongly aligned with areas of established French expertise: inclusive diffraction and inclusive quarkonium production. These channels offer clean signatures, robust theoretical interpretability, and direct sensitivity to fundamental QCD phenomena such as gluon saturation, heavy-quark dynamics, and the small-x structure of hadrons and nuclei. In addition, the workshop identified longer-term physics opportunities that will benefit from the full capabilities of the EIC after its ramp-up phase. These include accessing the three-dimensional structure of the pion through the Sullivan process and a broader program of exclusive three-body final states, both of which represent high-impact avenues for exploring hadronic structure and non-perturbative QCD. Together, the elements summarized in this report provide a coherent overview of the strategic priorities and scientific ambitions shaping the French community's contribution to the EIC physics program.
Comments:
10 pages, excluding the title page, author list, acknowledgements, and references; 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2602.19664 [pdf]
0 citations
15
[Submitted on 23 Feb 2026] (cross-list from hep-ph)
Thermodynamically consistent treatment of repulsive corrections in HRG
Somenath Pal🇮🇳
We reformulate the treatment of density-dependent chemical potential shifts appearing in excluded-volume implementations of the hadron resonance gas model. An auxiliary classical representation is constructed in which a common energy shift is determined by preserving the scalar number density, ensuring thermodynamic consistency. Hadron radii are parametrized through a liquid-drop inspired mass-radius relation with two parameters: the pion radius and a scaling exponent. The resulting framework reproduces lattice QCD results for lower-order conserved-charge susceptibilities at zero chemical potentials with only two adjustable parameters.
Comments:
7 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2602.19821 [pdf]
0 citations
16
[Submitted on 23 Feb 2026] (cross-list from hep-ph)
Unquenched Charmonium and Beyond
Zi-Yue Bai🇨🇳 · Dian-Yong Chen🇨🇳 · Qi-Huang · Xiang Liu🇨🇳 · Si-Qiang Luo🇨🇳 · Jun-Zhang Wang🇨🇳
The year 2024 marked the 50th anniversary of the discovery of the $J / ψ$ particle, which unveiled the charm quark and the charmonium spectrum, instigating the "November Revolution" in particle physics. This discovery catalyzed the development of quenched potential models, most notably the Cornell model, which provided a foundational quantitative description of the hadronic spectrum. However, the landscape of hadron spectroscopy has been profoundly transformed since the turn of the 21st century with the observation of numerous charmonium-like states, such as $X (3872)$ , which exhibit properties starkly at odds with quenched model predictions. These discrepancies, exemplified by the " $X (3872)$ low-mass puzzle" and the " $Y$ problem" associated with vector states like $Y (4260)$ , underscore the critical limitations of the quenched approximation and signal the necessity for a new theoretical paradigm. This review synthesizes recent advances in hadronic spectroscopy, arguing that the unquenched picture, which incorporates coupled-channel effects such as hadronic loops, is essential for a unified description of these new states and associated anomalies. We demonstrate how unquenched effects provide compelling solutions to long-standing puzzles in charmonium decays (e.g., the " $ρ π$ puzzle" and anomalous dipion transitions), predict and explain the existence of exotic charged states like $Z_{c} (3900)$ and $Z_{b} (10610)$ via mechanisms such as Initial Single Pion Emission, and offer a framework for understanding interactions between charmonia and with nucleons. Furthermore, we emphasize the universality of unquenched effects, extending their application to bottomonium and light-flavor sectors. As experimental precision continues to improve, we advocate for the systematic development of unquenched hadronic spectroscopy.
Comments:
217 pages, 134 figures, 21 tables, accepted by Physics Reports
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2602.19887 [pdf]
24 citations

Affiliations

first authorsco-authorsvia INSPIRE

Analytic continuation of Green's functions with a neural network

Evidence of Nuclear Urca Process in the Ocean of Neutron-Star Superburst MAXI J1752−457

Two nearby states in the X(3872) region: Resolving the radiative-decay ratio tension with ηc2​

Three-body molecular states composed of D(∗) and two nucleons

2025 EIC-France Workshop: Physics Highlights and Perspectives

Thermodynamically consistent treatment of repulsive corrections in HRG

Unquenched Charmonium and Beyond

Affiliations

Evidence of Nuclear Urca Process in the Ocean of Neutron-Star Superburst MAXI J1752 $-$ 457

Two nearby states in the $X (3872)$ region: Resolving the radiative-decay ratio tension with $η_{c 2}$

Three-body molecular states composed of $D^{(*)}$ and two nucleons