Nuclear Theory·nucl-th

Friday·June 12, 2026

13 papers—6 primary·7 cross-listed

07
[Submitted on 10 Jun 2026] (cross-list from nucl-ex)
Constraining the Low- $p_{T}$ $η / π^{0}$ Ratio for Direct-Photon Analyses with Blast-Wave Fits to $π$ , $K$ , and $p$ Spectra
Klaus Reygers · Andreas Kirchner · Aleksas Mazeliauskas
We predict the $η / π^{0}$ ratio at low $p_{T}$ ( $p_{T} ≲ 3 GeV / c$ ) using the measured charged $K / π$ ratio and model input from a blast-wave framework with feeddown contributions. This approach can provide improved, data-constrained background estimates for direct-photon and dilepton measurements in heavy-ion collisions. In this approach, the explicit modeling of radial flow and hadronic feeddown enables an uncertainty estimate for the low- $p_{T}$ extrapolation of the $η / π^{0}$ ratio. Using central Pb-Pb collisions at $s_{N N} = 2.76$ TeV as an example, we find that the $η$ -related decay-photon uncertainty at $p_{T} \approx 1 GeV / c$ is of order 10\% of the expected direct-photon signal.
Comments:
10 pages, 11 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2606.12619 [pdf]
0 citations
08
[Submitted on 10 Jun 2026] (cross-list from hep-th)
Analytic structure of the QCD phase diagram in the complex-temperature plane
Gokce Basar🇺🇸 · Vladimir V. Skokov🇺🇸
We study the analytic structure of the QCD phase diagram by treating temperature as a complex variable. The nearest Yang-Lee edge singularities in the complex $T$ plane bound the domain of analyticity of temperature-dependent thermodynamic observables and complement the more commonly studied singularities in the complex chemical-potential plane. Our analysis combines three complementary perspectives: universal critical scaling, a first-principles extraction from lattice-QCD data, and explicit illustrations in effective models. We illustrate the resulting structure in a random-matrix model and in a quark-meson model, where the singularity trajectories can be followed explicitly. At small real chemical potential, the leading complex-temperature singularity admits an analytic expansion in $μ^{2}$ , while near a critical point it crosses over to the universal Puiseux form dictated by Ising critical scaling. We show that the complex- $T$ and complex- $μ$ trajectories are controlled by the same scaling variables and mapping coefficients, so their comparison provides a stringent consistency test of critical-point searches and constrains the extent of the critical scaling regime. Finally, we analyze lattice-QCD data at $μ = 0$ using an iterated conformal-Pade approach and extract the continuum location of the nearest complex-temperature singularity. The result is consistent with the expectation that, at physical quark masses, the real part of the leading singularity lies between the chiral-limit transition temperature and the physical-mass chiral-susceptibility peak temperature, while its imaginary part remains nonzero.
Comments:
14 pages, 8 figures
Subjects:
High Energy Physics — Theory (hep-th); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2606.12622 [pdf]
PRD(2026)·0 citations
09
[Submitted on 11 Jun 2026] (cross-list from quant-ph)
Accidental Symmetry in the Tavis-Cummings Model via the Schwinger Boson Representation
Plato Deliyannis🇺🇸 · Iman Marvian🇺🇸
The Jaynes-Cummings (JC) Hamiltonian is a paradigmatic model of light-matter interaction and, more generally, qubit-boson interactions, widely used across atomic, optical, and superconducting qubit platforms. In the multi-qubit setting, where n qubits are identically coupled to a single boson mode, this interaction is known as the Tavis-Cummings (TC) Hamiltonian. The structure of the TC model is usually understood in terms of two standard symmetries: permutation invariance of the qubits and a U(1) symmetry associated with conservation of the total excitation number. Here we identify an additional, independent "accidental" symmetry of the TC Hamiltonian and construct the corresponding conserved observable. We show that, for n>2 qubits, this symmetry imposes strong constraints on the realizable unitary transformations. These constraints persist in the presence of the global $J_{z}$ Hamiltonian, but are removed by adding $J_{z}^{2}$ , even though $J_{z}^{2}$ preserves both permutation invariance and the U(1) symmetry. Finally, we explain the origin of this previously unnoticed symmetry using Schwinger's boson representation of angular momentum. These restrictions have important implications for controllability of the TC system and for its applications to quantum computing, which are investigated further in a companion paper.
Comments:
v1; 12 pages+ 1 page of appendices. Parts of the results were previously presented in arXiv:2506.03453, which has now been expanded and split
Subjects:
Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
arXiv:
2606.12813 [pdf]
0 citations
10
[Submitted on 11 Jun 2026] (cross-list from quant-ph)
Global Control with the Tavis-Cummings Interaction
Plato Deliyannis🇺🇸 · Iman Marvian🇺🇸
We study the controllability of a system of qubits under global control, where control pulses act identically on all qubits. Specifically, we consider a collection of qubits identically coupled to a single bosonic mode, or harmonic oscillator, via the Jaynes-Cummings interaction. This collective coupling, known as the Tavis-Cummings (TC) interaction, has been realized in several quantum computing platforms, including superconducting and atomic qubit systems. Although the qubits do not interact directly with one another, they can become entangled through their common coupling to the bosonic mode. We characterize the group of unitaries that can be implemented on the joint Hilbert space of the qubits and bosonic mode using the TC interaction together with a global $z$ field $J_{z}$ , corresponding to identical z rotations on all qubits. We show that for n>2 qubits the set of realizable unitaries is restricted by an "accidental" symmetry of the TC Hamiltonian, distinct from its "standard" U(1) and permutational symmetries. On the other hand, we find that the Hamiltonian $J_{z}^{2}$ breaks this accidental symmetry and, together with the TC interaction and $J_{z}$ , achieves semi-universality: it allows the implementation of arbitrary unitaries that respect permutational and U(1) symmetry, up to certain constraints on the center of the group. In a companion paper, we further analyze this remarkable accidental symmetry and show that it can be understood through Schwinger's bosonic model of angular momentum.
Comments:
v1: 27 pages + 15 pages of appendices. Parts of the results were previously presented in arXiv:2506.03453, which has now been expanded and split
Subjects:
Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
arXiv:
2606.12906 [pdf]
0 citations
11
[Submitted on 11 Jun 2026] (cross-list from hep-ph)
Nucleon matrix elements of axial anomaly, axial currents and pseudoscalar currents in the QCD sum rule
Janardan Prasad Singh🇮🇳
We have analyzed one-nucleon matrix elements of current-current correlators; the currents consist of pseudoscalar octet, isovector and isoscalar currents, axial anomaly, and axial isovector and isoscalar currents. Using QCD sum rules, the coupling constants of nucleon with each of these currents have been expressed in terms of nucleon matrix elements of quark, gluon and quark-gluon composite operators and moments of parton distribution function. On the phenomenological side, contribution from the non-diagonal matrix elements of operators between nucleon and its excited states or continuum states have also been accounted for. For the pseudoscalar coupling constants of the nucleon two expressions have been obtained in which one of them consists of only moments of parton distribution function but yielding approximately same numerical result as the other one. Of particular interest is the nucleon matrix element of axial anomaly which has been largely ignored in the current literature.
Comments:
28 pages, 14 figures and 3 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2606.12959 [pdf]
0 citations
12
[Submitted on 11 Jun 2026] (cross-list from hep-ph)
Transport coefficients of strongly interacting quark-gluon plasma including elastic and inelastic scattering within the dynamical quasiparticle model
Gaia Ingrosso🇩🇪 · Olga Soloveva🇩🇪 · Ilia Grishmanovskii🇩🇪 · Taesoo Song🇩🇪 · Elena Bratkovskaya🇩🇪
We study the impact of inelastic gluon-radiation and absorption processes on the transport coefficients of the quark-gluon plasma within the dynamical quasiparticle model (DQPM) in the temperature--baryon-chemical-potential plane $(T, μ_{B})$ . Extending the $2 \to 2$ baseline established in previous DQPM calculations, we include gluon-radiation $2 \to 3$ and the inverse gluon-absorption $3 \to 2$ scattering channels with massive partons and effective DQPM propagators and vertices. The corresponding momentum-dependent interaction rates and relaxation times are used to calculate the shear viscosity, bulk viscosity, electric conductivity, and baryon diffusion coefficient as functions of temperature $T$ and baryon chemical potential $μ_{B}$ . Within the relaxation time approximation, we find that $2 \leftrightarrow 3$ contributions systematically reduce all considered transport coefficients relative to the $2 \to 2$ only results, in accordance with the decrease of the relaxation times. In the thermal regime explored here, however, this reduction remains moderate, since the investigated inelastic rates stay below the $2 \to 2$ ones over the considered $(T, μ_{B})$ range. The inelastic channels become more relevant mainly for partonic scatterings at large momenta, which are thermally suppressed in the strongly interacting QGP. At $μ_{B} = 0$ , the resulting $η / s$ , $ζ / s$ , and $σ_{Q} / T$ are compatible with available lattice-QCD estimates within uncertainties. At finite $μ_{B}$ , our results provide predictions for the transport properties of QCD matter relevant for beam-energy-scan programs.
Comments:
14 pages, 10 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2606.13363 [pdf]
0 citations
13
[Submitted on 11 Jun 2026] (cross-list from astro-ph.HE)
Classification of Compact Stars via Machine Learning and Neural Network Models
D. Neraki🇬🇷 · G. Koufetidis🇬🇷 · I. Stergakis🇬🇷 · Th. Diakonidis🇬🇷 · Ch.C. Moustakidis🇬🇷
Recent advances in multimessenger astronomy, particularly through gravitational-wave observations of compact-object mergers, have significantly improved our understanding of dense matter. Nevertheless, the internal composition of compact stars remains uncertain. Depending on the underlying equation of state (EoS), these objects may be neutron stars composed primarily of nucleons, quark stars made of deconfined quark matter, or hybrid stars containing both hadronic and quark phases. More exotic constituents, such as hyperons, meson condensates, or dark matter, have also been proposed. In this work, we investigate whether the internal composition of compact stars can be inferred from observable quantities, including mass, radius, and tidal deformability. To address this problem, we employ machine-learning and deep-learning techniques trained on a larg dataset of EoSs describing both neutron stars and quark stars. From these EoSs, we generate the corresponding mass radius relations spanning a wide range of stellar configurations. The resulting dataset is used to train and evaluate classification models aimed at identifying the nature of compact objects from their macroscopic properties. Our results indicate that suitable combinations of observables can distinguish neutron stars from quark stars with very high accuracy. These findings demonstrate the potential of machine-learning approaches as tools for probing the composition of dense matter. However, further studies incorporating additional scenarios, including hybrid stars and other exotic forms of matter, are required to establish the robustness and general applicability of this methodology.
Comments:
22 pages, 12 figures, 15 tables. Any comments are welcome
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
2606.13369 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Constraining the Low-pT​ η/π0 Ratio for Direct-Photon Analyses with Blast-Wave Fits to π, K, and p Spectra

Analytic structure of the QCD phase diagram in the complex-temperature plane

Accidental Symmetry in the Tavis-Cummings Model via the Schwinger Boson Representation

Global Control with the Tavis-Cummings Interaction

Nucleon matrix elements of axial anomaly, axial currents and pseudoscalar currents in the QCD sum rule

Transport coefficients of strongly interacting quark-gluon plasma including elastic and inelastic scattering within the dynamical quasiparticle model

Classification of Compact Stars via Machine Learning and Neural Network Models

Affiliations

Constraining the Low- $p_{T}$ $η / π^{0}$ Ratio for Direct-Photon Analyses with Blast-Wave Fits to $π$ , $K$ , and $p$ Spectra