Nuclear Theory·nucl-th

Tuesday·August 26, 2025

16 papers—11 primary·5 cross-listed

01
Hubble's Law in Heavy Ion Collisions
N.V. Kolomoyets🇷🇺 · O.V. Teryaev🇷🇺 · V. Voronyuk🇷🇺
The evolution of the "microscopic" Hubble parameter related to the expansion of matter born in heavy-ion collisions was obtained for nucleons and pions. The calculations were carried out within the parton-hadron-string dynamics (PHSD) transport model. Au+Au collisions with $s_{N N} = 7.8$ GeV at $b = 2.5, 5.0, 7.5$ , and $10.0$ fm were considered. A new method for determining the "microscopic" Hubble parameter from simulated data was used. The ballistic motion was obtained for the longitudinal direction after the separation of the nuclei. In earlier times, the evolution of the "microscopic" Hubble parameter in this direction was more complicated. For transverse directions, an exponential low-time asymptotics of the Hubble parameter was observed. The obtained values of the "microscopic" Hubble parameter are about 40 orders of magnitude higher than the cosmological Hubble constant.
nucl-thhep-phPRC(2025)·0 citations
02
An Undergraduate Approach to the Quantum Hadrodynamics and the Physics of Neutron Stars
Luiz L. Lopes
In this tutorial, I discuss how to model a neutron star from the Quantum Hadrodynamics microscopic approach. After a brief discussion about hydrostatic equilibrium, I discuss the role of each meson of the model and how to calculate the corresponding equation of state and the expected values. Each meson is introduced individually. Its effects are analyzed from both an analytical and a numerical point of view. To explicitly show the effects of a given meson, the coupling constant is varied in an arbitrary range before being fixed to reproduce well-known constraints. This work is intended for late undergraduate students as well as early graduate students. The equation of states is obtained from the statistical mechanics formalism, which is more familiar to students at this stage of their research career, instead of the traditional quantum field theory formalism.
nucl-thastro-ph.HEhep-phUniverse(2025)·5 citations
03
Probing Dynamical Electrical Conductivity via Dilepton Emission: A Kinetic theory approach
Ashutosh Dwibedi🇮🇳 · Ankit Kumar Panda🇮🇳 · Sabyasachi Ghosh🇮🇳 · Victor Roy🇮🇳
Dileptons serve as a clean and penetrating probe of the Quark--Gluon Plasma created in high-energy heavy-ion collisions. In this work, we investigate thermal dilepton spectra and their elliptic flow through the dynamical conductivity that governs the production rate. The conductivity is obtained from the trace of the spectral function within relativistic kinetic theory using the Relaxation Time Approximation. This allows us to derive for the first time an analytical expression for the dilepton rate with explicit dependence on the relaxation time of quark-antiquark interactions. We find a non-monotonic dependence of the dilepton rate on the relaxation time and compare the resulting transverse momentum, invariant mass spectra and elliptic flow with previous quantum field theory results. The spectra and elliptic flow are obtained by integrating the rate over the full spacetime volume of the evolving medium, using temperature and flow profiles from realistic MUSIC hydrodynamic simulations without considering the effect of magnetic fields in the profiles itself. However, we study the role of an external space-time dependent magnetic field by making the conductivity anisotropic. At small relaxation times, magnetic fields have negligible impact, while for larger relaxation times and stronger initial fields, modifications of up to $\sim$ 20\% appear in both spectra and elliptic flow. Assuming instead a constant magnetic field of $\sim 1 m_{π}^{2}$ at large relaxation times yields more modest effects, with changes of about 10\% in spectra and 5\% in elliptic flow.
nucl-thPRD(2026)·8 citations
04
Properties of Isoscalar Giant Multipole Resonances in medium-mass one-closed-shell nuclei: A semi-microscopic description
M.L. Gorelik · M.H. Urin
The semi-microscopic particle-hole dispersive optical model, having unique abilities in describing main properties of various giant resonances in medium-heavy-mass spherical nuclei, is applied to a number of Isoscalar Giant Multipole Resonances in one-closed-shell nuclei 58Ni, 120Sn, and 142Nd. Some of the calculation results are compared with respective experimental data, including those obtained just recently. Special attention is paid to a comparison of calculated isoscalar multipole strength functions with the respective experimental strength distributions in a wide excitation-energy interval.
nucl-thPRC(2026)·1 citation
05
Effects of Geometric configuration in relativistic isobaric collisions at $s_{N N} = 200$ GeV
Akash Das🇮🇳 · Satya Ranjan Nayak🇮🇳 · B. K. Singh🇮🇳
In this work, we present a study on the effects of nuclear deformation ( $β_{2}$ , $β_{3}$ ) and surface diffuseness ( $a$ ) on the charged hadron multiplicity ( $N_{ch}$ ) and elliptic flow ( $v_{2}$ ), obtained in symmetric isobaric collisions of $_{44}^{96} Ru +_{44}^{96} Ru$ and $_{40}^{96} Zr +_{40}^{96} Zr$ . The two extreme configurations (tip-tip and body-body) were used to determine the correlation between the final state observables and initial geometry using the HYDJET++ model. The octupole deformation parameter ( $β_{3}$ ) enhances $N_{ch}$ in central tip-tip Zr+Zr collisions and suppresses it in peripheral ones. In mid-central to peripheral body-body Zr+Zr collisions, $β_{3}$ leads to a reduction in charged hadron production. Surface-diffuseness ( $a$ ), along with quadrapole deformation ( $β_{2}$ ), also shows a significant impact on multiplicity and elliptic flow. The octupole deformation enhances elliptic flow in Zr's body-body collisions. Results are compared with the STAR blind-analysis data where available.
nucl-thhep-phEur.Phys.J.Plus(2026)·0 citations
06
Probing in-medium effect via giant dipole resonance in the extended quantum molecular dynamics model
Chen-Zhong Shi · Xiang-Zhou Cai · Yu-Gang Ma
Rather than using the geometric method employed in the original Extended Quantum Molecular Dynamics (EQMD) model, this article employs a stochastic approach to analyze the collision term and examine the width of the isovector giant dipole resonance (GDR) in $^{208}$ Pb. Based on the ``soft" EQMD model, which we recently developed, the response and strength functions are self-consistently determined for various symmetry energy coefficients and in-medium reduction factor values. The results confirm that the peak position and GDR width in $^{208}$ Pb are highly sensitive to the symmetry energy and the in-medium nucleon-nucleon ({\it NN}) cross section. This provides an opportunity to study the nuclear equation of state (EoS) and the medium effect. A significant reduction in free {\it NN} elastic cross sections within the medium is necessary to accurately reproduce the GDR width, as demonstrated by a comparison with the evaluation data.
nucl-thnucl-exPRC(2026)·0 citations
07
Validity of relativistic hydrodynamics beyond local equilibrium
Reghukrishnan Gangadharan🇮🇳
We examine the applicability of relativistic hydrodynamics far from equilibrium by constructing formal solutions of the Boltzmann moment equations in the relaxation time approximation. These solutions naturally decompose into a divergent gradient series and exponentially decaying non-perturbative modes that encode initial conditions. The non-perturbative contributions are essential for understanding causality, the divergence of the gradient series, and the unexpected effectiveness of relativistic hydrodynamics far from equilibrium. In the 0+1D Bjorken scenario, we demonstrate that the exact evolution of non-equilibrium terms shares the same structural form as the gradient expansion, differing only through modified transport coefficients that reflect both initial data and free-streaming dynamics. Extending to 3+1D, we find that hydrodynamics remains effective not because the system is close to equilibrium, but because it interpolates smoothly between free streaming and collective behavior. This perspective offers a natural explanation for the remarkable success of hydrodynamics in modeling quark-gluon plasma evolution.
nucl-thhep-thPRD(2026)·0 citations
08
Assessing Convergence Patterns Across Modern Nucleon-Nucleon Potentials
P. J. Millican · R. J. Furnstahl · J. A. Melendez · D. R. Phillips
The BUQEYE model for correlated effective field theory (EFT) truncation errors assumes a regular pattern of dimensionless coefficients extracted from order-by-order observable calculations. This enables results from lower orders to inform statistical predictions for error estimates of omitted higher orders. We test the model for multiple chiral EFT ( $χ$ EFT) nucleon-nucleon (NN) potentials using a suite of six common NN scattering observables represented as functions of relative momentum and scattering angle. First, we flag irregularity in the convergence patterns of potentials with so-called "soft" regulator scales, namely that the sizes of the coefficients in the observables' expansions are mismatched between the even and odd orders. Second, we test the BUQEYE model's assumption of Gaussian process (GP) stationarity against the data and find that the GP's correlation structure as encoded in its length scale is nonstationary: The GP length scale in the angular dimension $ℓ_{θ}$ is approximately inversely proportional to the relative momentum of the scattering process. After we remediate this issue by allowing $ℓ_{θ}$ to vary with momentum, diagnostics show significant improvement, validating the application of the BUQEYE model after this modification. Third, we find that good performance of the BUQEYE model relies on properly choosing the $χ$ EFT breakdown scale $Λ_{b}$ . With $m_{eff}$ held fixed at the physical pion mass we find $Λ_{b} = 600$ -- $750$ MeV for various N $^{3}$ LO interactions. Statistically consistent distributions for $Λ_{b}$ across orders are only found for the SMS potential at a regulator scale of 450 or 500 MeV. All our results can be reproduced using a publicly available Jupyter notebook, which can be straightforwardly modified to analyze other $χ$ EFT NN potentials.
nucl-thhep-phphysics.data-anPRC(2026)·8 citations
09
Stationary States for Fermions in an External Electric Field
Xuan Zhao🇨🇳 · Yi Wang🇨🇳 · Pengfei Zhuang🇨🇳
We present a relativistic analysis of fermions in an external electric field by non-perturbatively solving the Dirac equation with a static gauge. Different from the magnetic field effect, the fermion wave function in an electric field oscillates asymptotically, which results in the absence of bound states in an infinite system. For a confined fermion, the confinement is gradually canceled by the electric field, and the fermion becomes deconfined when the electric coupling is stronger than the confinement coupling. However, a fermion in an electric field can be confined to a finite system by applying the MIT bag boundary condition, namely, the disappearing normal component of the probability current at the boundary. The solutions obtained can serve as a basis for calculating dynamical processes in the presence of a strong electric field, such as those occurring in the early stage of relativistic heavy-ion collisions, where an extremely strong electric field is expected to be generated.
nucl-thEPJC(2026)·1 citation
10
New shell-model calculations of the $δ_{C}$ correction to superallowed $0^{+} \to 0^{+}$ nuclear $β$ decay and standard-model implications
L. Xayavong🇰🇷 · N. A. Smirnova🇫🇷 · F. Nowacki🇫🇷
Refined calculations of the radial mismatch correction, $δ_{C 2}$ , to superallowed $0^{+} \to 0^{+}$ nuclear $β$ decay are performed using the shell model with realistic Woods-Saxon radial wave functions. Two important improvements are introduced: i) charge radii used to constrain the length parameter are evaluated within a generalized formula, where proton occupation numbers are substituted by sums of spectroscopic factors, while radial wave functions are required to match separation energies with respect to the intermediate $(A - 1)$ -nucleon states by adjusting parameters such as the potential depth; ii) configuration mixing wave functions and energies for many-particle states are obtained through the diagonalization of well-established effective interactions in large configuration spaces without truncation. Furthermore, a variation of $\pm 0.1$ \,fm in the surface diffuseness parameter is now incorporated as a source of uncertainty. The present results are generally in fairly good agreement with those from previous studies. As an exception, the $δ_{C 2}$ value obtained for $^{18}$ Ne is smaller by approximately a factor of two, principally due to the updated charge-radius treatment. A reduction is also observed in most cases with $A \geq 38$ , through the deviations generally remain within the newly assigned error bars. The smaller isospin-mixing counterpart, $δ_{C 1}$ , is strongly interaction-dependent, roughly following an inverse-square law with respect to the energy separation between the lowest admixed levels. Therefore, an additional procedure to ensure isobaric displacements within the isospin multiplets appears to be indispensable. Our results for $δ_{C 2}$ lead to a new averaged $F t$ value of $3073.11 (99)_{s t a t} (36)_{δ_{R}^{'}} (173)_{δ_{N S}}$ ~s with $χ^{2} / ν = 0.624$ . The corresponding $∣ V_{u d} ∣$ value is 0.97359(33).
nucl-thPRC(2025)·2 citations
11
Two-flavored heavy mesons' nuclear bound states
G. N. Zeminiani🇧🇷 · S. L. P. G. Beres🇧🇷 · K. Tsushima🇧🇷
We calculate the $B_{c}$ - and $B_{s}$ -nucleus bound state energies and coordinate space radial wave functions by solving the Klein-Gordon equation in momentum space. The attractive strong potentials for the $B_{c}$ and $B_{s}$ mesons in nuclei are calculated from the respective mass shifts of these mesons in nuclear matter using a local density approximation. This negative mass shift may be regarded as a signature of partial restoration of chiral symmetry in medium in an empirical sense, because the origin of the negative mass shift in the present study is not directly related to the chiral symmetry mechanism.
nucl-thhep-exhep-phnucl-exPoS(2026)·0 citations
12
$r$ -process Heating Feedback on Disk Outflows from Neutron Star Mergers
Li-Ting Ma · Kuo-Chuan Pan · Meng-Ru Wu · Rodrigo Fernández
Neutron star mergers produce $r$ -process elements, with yields that are sensitive to the kinematic and thermodynamic properties of the ejecta. These ejecta properties are potentially affected by dynamically-important feedback from $r$ -process heating, which is usually not coupled to the hydrodynamics in post-merger simulations modeling the ejecta launching and expansion. The multi-messenger detection of GW170817 showed the importance of producing reliable ejecta predictions, to maximize the diagnostic potential of future events. In this paper, we develop a prescription for including $r$ -process heating as a source term in the hydrodynamic equations. This prescription depends on local fluid properties and on the $Y_{e}$ history as recorded by dedicated tracer particles, which exchange information with the grid using the Cloud-in-Cell method. The method is implemented in long-term viscous hydrodynamic simulations of accretion disk outflows to investigate its feedback on ejecta properties. We find that $r$ -process heating can increase the unbound disk ejecta mass by $\sim 10%$ relative to a baseline case that only considers alpha particle recombination. Nuclear heating also enhances the radial velocity of the ejecta with $Y_{e} < 0.25$ by up to a factor of two, while concurrently suppressing marginally-bound convective ejecta.
↳ astro-ph.HEnucl-thApJ(2026)·3 citations
13
A Journey of Seeking Pressure and Forces in the Nucleon
Xiangdong Ji🇺🇸 · Chen Yang🇺🇸
Momentum current density (MCD) $T^{ij}$ is a general physics concept describing the momentum conservation through momentum flow generated from both the kinetic motion of particles and the interacting forces among them. It has been suggested by M. Polyakov et al. that the MCD in the nucleon, characterized by the form factor $C / D$ of the QCD energy-momentum tensor, can be interpreted as the pressure and shear forces between adjacent parts of the system because the nucleon interior approximates a continuous medium. While intuitively appealing, we find that the interpretation is hard to justify from a detailed examination of the physical mechanisms for the momentum flow in QCD. After reviewing through a broad range of classical and quantum systems, we find that while thermal and/or quantum average of isotropic motion contributes to kinetic MCD a pressure term proportional to $δ^{ij}$ , when there is an anisotropic motion, the pressure cannot simply be identified from the MCD tensor. Furthermore, kinetic pressure cannot be considered as the surface force between adjacent parts of a system. More importantly, at the scale of the nucleon dimension, the color forces among quarks and gluons is by no means short-ranged as in a continuous medium, and the resulting interaction MCD cannot be interpreted as normal or shear ``stress'' force, although an isotropic term from the QCD trace anomaly may be interpreted as a ``vacuum pressure.'' Following our previous study of force densities through divergences of kinetic MCDs, we affirm that the vacuum pressure term provides a confining potential on the quarks through color Lorentz forces.
↳ hep-phhep-latnucl-thNPB(2026)·30 citations
14
Baryon Electric Charge Correlation as QCD Magnetometer
Heng-Tong Ding🇨🇳 · Jin-Biao Gu🇨🇳 · Arpith Kumar🇨🇳 · Sheng-Tai Li🇨🇳
The detection of strong magnetic fields in peripheral heavy-ion collisions is crucial for observing effects such as the chiral magnetic effect but has proven exceptionally difficult. To address this, we propose the baryon electric charge correlation $χ_{11}^{BQ}$ and the chemical potential ratio $μ_{Q} / μ_{B}$ as sensitive probes of magnetic fields, based on (2+1)-flavor lattice QCD simulations at the physical pion mass. Along the transition line, $χ_{11}^{BQ}$ and $(μ_{Q} / μ_{B})_{LO}$ in Pb-Pb collisions increase by factors of 2.1 and 2.4 at $e B ≃ 8 M_{π}^{2}$ , respectively. To bridge theoretical predictions with experimental observables, we implement systematic kinematic cuts that emulate detector acceptances of the STAR and ALICE experiments within the hadron resonance gas model. This allows us to construct experimentally relevant proxy observables. Furthermore, we demonstrate that $(μ_{Q} / μ_{B})_{LO}$ is also sensitive to the collision system, showing a $1.5$ -fold increase from Zr-Zr to Ru-Ru isobar collisions. Our findings offer new insights into thermo-magnetic effects and provide experimentally relevant guidance for the detection of magnetic fields in heavy-ion collisions.
↳ hep-lathep-phnucl-exnucl-thEPJ Web Conf.(2026)·2 citations
15
Spontaneous breaking of global U(1) symmetry in an interacting Bose gas under rigid rotation
E. Siri🇮🇷 · N. Sadooghi🇮🇷
We investigate the impact of rigid rotation on the spontaneous breaking of U(1) symmetry in a Bose gas, which is described by a self-interacting complex scalar field Lagrangian. Rigid rotation is introduced through a specific metric that explicitly depends on the angular velocity $Ω$ . We begin by determining the free propagator for this model at finite temperature $T$ and chemical potential $μ$ . Using this propagator, we calculate the thermodynamic potential in terms of an energy dispersion relation $ϵ_{k}$ . It is found that in both the U(1) symmetric phase and the symmetry-broken phase, two energy branches emerge. In the symmetry-broken phase, they are identified with a massive phonon and a massless roton mode. Notably, rotation does not alter $ϵ_{k}$ at low momentum. Setting $μ = 0$ , we use the total thermodynamic potential, which includes classical, thermal, vacuum, and nonperturbative ring contributions, to explore how the condensate depends on $T$ and $Ω$ . We first focus on the classical and thermal parts of the thermodynamic potential and find that the critical temperature of the U(1) phase transition scales as $Ω^{1/3}$ . By identifying the (pseudo-)Goldstone and non-Goldstone modes of this model with $π$ and $σ$ mesons, we calculate the $T$ and $Ω$ dependence of masses $m_{π}$ and $m_{σ}$ . We demonstrate that the Goldstone theorem holds only when the one-loop (thermal) corrections to $m_{σ}$ and $m_{π}$ are taken into account. We further explore the $T$ and $Ω$ dependence of the condensate, determine the $σ$ dissociation temperatures for fixed $Ω$ , and compare them with the critical temperature of the phase transition. Additionally, we emphasize the role played by the nonperturbative ring potential, especially in altering the order of the phase transition with and without rotation.
↳ hep-phcond-mat.quant-gashep-thnucl-th4 citations
16
Sensitivity of neutrinoless double beta decays from a combined analysis of ground and excited states
C. R. Ding🇨🇳 · K. Han🇨🇳 · S.B. Wang🇨🇳 · J. M. Yao🇨🇳
Next-generation neutrinoless double-beta ( $0 ν β β$ ) decay experiments, with projected half-life sensitivities approaching $1 0^{28}$ years, aim to probe the entire parameter space of the inverted neutrino mass ordering in the light-neutrino-exchange scenario. However, this reach remains uncertain by the substantial model dependence of the nuclear matrix elements (NMEs). In this work, we propose a strategy based on a combined analysis of $0 ν β β$ decays to both the ground state and the first excited $0^{+}$ state of the daughter nucleus. We show that such a multi-channel approach can significantly enhance experimental sensitivity, depending on the underlying NME predictions. This method is particularly well-suited for large liquid xenon detectors, such as the proposed PandaX-xT and XLZD experiments, which can efficiently identify transitions of $^{136}$ Xe to excited states. Our results highlight the importance of exploiting multiple decay channels in future $0 ν β β$ searches to maximize their discovery potential.
↳ hep-phhep-exnucl-exnucl-thPLB(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE