Nuclear Theory·nucl-th

Friday·November 7, 2025

8 papers—4 primary·4 cross-listed

01
Predictions of baryon directed flow in heavy-ion collisions at high baryon density
Yuri B. Ivanov🇷🇺
Predictions of the proton directed flow ( $v_{1}$ ) in semicentral Au+Au collisions in the energy range between 4.5 and 7.7 GeV are done. The calculations are performed within the model of three-fluid dynamics with crossover equation of state, which well reproduces the proton $v_{1}$ both below 4.5 GeV and above 7.7 GeV, as well as bulk observables in the energy range of interest. It is predicted that the proton flow evolves non-monotonously. At the energy of 7.2 GeV it exhibits antiflow (i.e. negative slope of $v_{1} (y)$ ) in the midrapidity. At 7.7 GeV, the flow returns to the normal pattern in accordance with the STAR data. The midrapidity $v_{1}$ -slope excitation functions within the first-order phase and crossover transitions to quark-gluon phase (QGP) turn out to be qualitatively similar, but the amplitude of the wiggle in the crossover scenario is much smaller than that in the strong first-order phase transition. Therefore, the change of sign followed by minimum at 7.2 GeV in the $v_{1}$ -slope excitation function indicates onset of (weak phase or crossover) transition to QGP. The second change of the sign around 10 GeV results from interplay between incomplete baryon stopping and transverse expansion of the system.
nucl-thhep-phnucl-exPRC(2026)·1 citation
02
Chiral-scale effective field theory for dense and thermal systems
Jia-Ying Xiong🇨🇳 · Yao Ma🇨🇳 · Bing-Kai Sheng🇨🇳 · Yong-Liang Ma🇨🇳
We established a new power counting scheme, chiral-scale density counting (CSDC) rules, for the application of the chiral-scale effective field theory to nuclear matter at finite densities and temperatures. Within this framework, the free fermion gas is at the leading order, while one-boson-exchange interactions appear at the next-to-leading order, and the multi-meson couplings are at higher orders. Then, we applied the CSDC rules to study the nuclear matter properties, and estimated the valid regions of the CSDC rules. It was found that the zero temperature symmetric nuclear matter properties around saturation density and the critical temperature of liquid-gas phase transition can be captured by an appropriate choice of CSDC orders, and the results beyond these regions are align with the chiral nuclear force. Moreover, the evolution of scale symmetry was found to be consistent with previous studies. The results of this work indicate that the quantum corrections may be crucial in the studies of nuclear matter in a wide density region.
nucl-thPRD(2026)·4 citations
03
The size of the quark-gluon plasma in ultracentral collisions: impact of initial density fluctuations on the average transverse momentum
Fabian Zhou🇩🇪 · Giuliano Giacalone🇨🇭 · Jean-Yves Ollitrault🇫🇷
Recent experiments have shown that the mean transverse momentum $⟨ p_{T} ⟩$ of outgoing particles increases as a function of the particle multiplicity in ultracentral nucleus-nucleus collisions at collider energies. This increase was originally predicted on the basis of simulations where the multiplicity increase occurred at constant volume, so that it implied a larger density and temperature. However, recent state-of-the-art simulations have shown that, for some models of initial condition, the volume may vary with the multiplicity in ultracentral collisions. We elucidate this effect by analytically relating the variation of the volume to the radial distribution of the one- and two-point functions of the fluctuating density field. We show that the volume variation is small if the total entropy of the ultracentral collisions scales with the mass number of the colliding isotopes. We argue that probing detailed transverse distributions of initial-state fluctuations through the ultracentral $⟨ p_{T} ⟩$ has nontrivial implications for models of nuclear structure and of the pre-equilibrium stages.
nucl-thhep-phnucl-exPRC(2026)·4 citations
04
Electromagnetic and Exotic Moments in Nuclear DFT
J. Dobaczewski · B.C. Backes · R.P. de Groote · A. Restrepo-Giraldo · X. Sun · H. Wibowo
Electromagnetic interactions serve as essential probes for studying and testing our understanding of the atomic nucleus, as they reveal emergent properties across the nuclear chart. We analyse their corresponding observables, which relate to charge and current distributions in nuclei expressed through their multipole components. We focus on theoretical results obtained within nuclear density functional theory (DFT) to derive self-consistent, symmetry-restored nuclear wave functions along with their spectroscopic multipole moments. We demonstrate how these compare with experimental data. We also discuss potential improvements in the formulation of magnetic dipole operators by including two-body meson-exchange contributions. Discussions of exotic symmetry-breaking moments emphasise their importance for understanding fine details of fundamental nuclear interactions. Detailed derivations are provided in the accompanying Supplemental Material.
nucl-th4 citations
05
Light new physics and the $τ$ lepton dipole moments
Martin Hoferichter🇨🇭 · Gabriele Levati🇨🇭
Testing New-Physics (NP) scenarios that couple predominantly to the third generation is notoriously difficult experimentally, as exemplified by comparing limits for the $τ$ lepton dipole moments to those of electrons and muons. In this case, extracting limits from processes such as $e^{+} e^{-} \to τ^{+} τ^{-}$ often relies on effective-field-theory (EFT) arguments, which allow for model-independent statements, but only apply if the NP scale is sufficiently large compared to the center-of-mass energy. In this work we offer a comprehensive analysis of light NP contributions to the $τ$ dipole moments, providing a detailed account of the interpretation of asymmetry measurements in $e^{+} e^{-} \to τ^{+} τ^{-}$ that are tailored towards the extraction of dipole moments, for the test cases of new light spin- $0$ and spin- $1$ bosons. Moreover, we study the decoupling to the EFT limit in these scenarios and discuss the complementarity to constraints from other related processes, such as production in $e^{+} e^{-}$ reactions. While covering a wide range of light NP scenarios, as specific case study we present a detailed discussion of a tauphilic gauge vector boson at Belle II.
↳ hep-phhep-exnucl-thPRD(2026)·12 citations
06
Characterizing the initial state of hydrodynamics in pp and pA collisions
Gabriel Rabelo-Soares🇧🇷 · Gojko Vujanovic🇨🇦 · Giorgio Torrieri🇧🇷
The observation of seeming hydrodynamic-like behavior in proton-proton and proton-nucleus collisions presents us with the conceptual problem of how the initial state of such a hydrodynamic evolution should be characterized. This is an issue because, while nuclei can reasonably be approximated as ``large'' systems w.r.t. the characteristic Fermi momentum of their constituents, this is no longer true for nucleons. Hence, one would need to match a ``quantum'' theory, whose observables are described via highly non-commuting operators, to a ``classical'' hydrodynamics. Operationally assuming a ``fast'' thermalization, we survey what kind of object is best suited to such a matching condition. We show that it cannot be any of the objects usually associated with ``the 3D structure of the nucleon'' but rather a measure associated with entanglement entropy.
↳ hep-phnucl-th3 citations
07
Exclusive photoproduction of a di-meson pair with large invariant mass
Saad Nabeebaccus🇬🇧 · David Perez🇫🇷 · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷
We consider the exclusive photoproduction of a di-meson pair with large invariant mass, $γ N \to N^{'} M_{1} M_{2}$ , in the framework of collinear factorisation. The mesons considered $M_{1}$ and $M_{2}$ are either pions or rho mesons, charged or neutral. We consider the kinematic regime characterised by a large invariant mass of the two-meson system, and a small deflection of the nucleon in the centre-of-mass frame. In this kinematic domain, the amplitude factorises into a perturbative hard part and non-perturbative parts described by Generalised Parton Distributions (GPDs) and Distribution Amplitudes (DAs). We automate the calculation of the fully differential cross section at leading twist and leading order, and we present some numerical results at JLab 12 GeV kinematics. This class of processes provides yet more exclusive $2 \to 3$ channels that can be used to extract GPDs.
↳ hep-phhep-exnucl-exnucl-th1 citation
08
Emergence of kaonium as a sharp resonance in photon-photon to meson-meson cross-sections
Alireza Beygi🇩🇪 · S. P. Klevansky🇩🇪 · R. H. Lemmer🇿🇦
We calculate the binding energies of the hypothetical mesonic atom, $K^{+} K^{-}$ (kaonium), using the $K^{+} K^{-} \to K^{+} K^{-}$ elastic scattering amplitude. Our findings are in line with previously reported results, which involve solving an eigenvalue equation of the Kudryavtsev-Popov type. Using chiral perturbation theory, we show that kaonium manifests itself as a sharp resonance around 992 MeV accompanying $f_{0} (980)$ or $a_{0} (980)$ in cross-sections for processes $γ γ \to π^{0} π^{0}$ or $γ γ \to π^{0} η$ . The latter process is particularly striking: the peak at the kaonium resonance energy is highly pronounced, with the ratio of the cross-sections $σ (γ γ \to π^{0} η) / σ (γ γ \to π^{0} π^{0}) \approx 9$ . Due to the short lifetime of kaonium ( $\sim 1 0^{- 18}$ s) and its small decay width ( $\sim 0.4$ keV), direct detection of this exotic atom poses a significant challenge and requires high experimental resolution. However, we show that once the formation of kaonium is considered in the cross-section, a better fit to the available experimental data is obtained.
↳ hep-phnucl-thPRD(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE