Nuclear Theory·nucl-th

Wed·Sep 30, 2026Wednesday·September 30, 2026

10 papers—4 primary·6 cross-listed

01
Semiclassical description of quadrupole-hexadecapole correlation in nuclear shape evolution
Kenichiro Arita
Background: Theoretical investigations of nuclear shapes with realistic effective interactions or mean field potentials have suggested a remarkable systematics in the hexadecapole shape evolution with varying particle number: Within each single-particle shell, from one spherical magic number to the next, a diamond type (beta_4>0) appears in the first half, and then turn into oblong type (beta_4<0) in the second half. Purpose: Nuclear deformation is essentially governed by the single-particle shell structure. In semiclassical periodic orbit theory (POT), level density is expressed as the sum over contributions from classical periodic orbits, and the origins of the gross shell structures can be understood by the contribution of one or a few shortest orbits. Using the POT, I examine how the hexadecapole degree of freedom affect the contribution of the orbits to the deformed shell structure through their bifurcations to explain the mechanism of above shape evolution. Methods: Ground state deformations are systematically investigated by the shell correction method, taking account of axially symmetric quadrupole and hexadecapole shape degrees of freedom. For simplicity, I employ two simplest mean field potentials to obtain the shell corrections: the oscillator and the cavity (infinite well) potentials. After confirming the the systematics in shape evolution under these simplest mean-field models, semiclassical analyses are made, focusing on the role of PO bifurcation. Results and conclusions: Systematics in the hexadecapole shape evolution in each single-particle shell is clearly explained by the bifurcations of two different types of periodic orbits in the cavity model, which suggest strong correlation between quadrupole and hexadecapole parameters. This also ensures the mechanism of nuclear prolate-shape predominance within this simple potential model.
nucl-th
02
Elliptic flow in an expanding and rotating fireball
Ashutosh Dwibedi · Anupam Panja · Sabyasachi Ghosh
We investigate the role of initial orbital angular momentum in generating elliptic flow in off-central heavy-ion collisions. The conventional expanding fireball picture is extended for the first time to a simultaneously expanding and rotating fireball characterized by an angular velocity. Spherical and spheroidal emission geometries with two different rotating flow profiles, reminiscent of global and differential rotation, are considered for our investigation. While the transverse-momentum spectra at midrapidity are largely insensitive to the geometry and flow profile for realistic values of angular velocity, the elliptic flow is strongly affected by anisotropic expansion and rotation. A spherical fireball generates elliptic flow solely through the momentum anisotropy induced by rotation, but its magnitude remains below the observed values for realistic angular velocities. In contrast, an anisotropically expanding and rotating spheroidal fireball exhibits a $\sim 10%$ enhancement of elliptic flow for $s_{NN} = 7.7$ GeV, which reduces to a $2%$ for $s_{NN} = 39$ GeV relative to its non-rotating counterpart. Within our fireball framework, this indicates that vorticity can contribute at the $2 - 10%$ level to the observed elliptic flow.
nucl-th
03
Short-range correlated pairs from nucleon density profiles as a new probe of the nuclear equation of state
L. Ponnath · N. Barnea · I. Korover · S. Paschalis · M. Petri · E. Piasetzky · X. Roca-Maza · S. Typel · I. Wischnevsky Shlush
We investigate to what extent the observed nuclear systematics of Short-Range Correlations (SRCs) can be described by the geometry of the underlying proton and neutron density distributions. Building on previous connections between nuclear SRC contacts and one-body densities, we formulate an explicit density-overlap representation in which proton--proton, proton--neutron, and neutron--neutron SRC source terms are constructed from the full spatial density profiles obtained with Energy Density Functionals (EDFs). The framework contains two global parameters describing the overall SRC pair formation strength and the relative contribution of the spin-singlet channel, while the nucleus-dependent evolution is generated by the density-overlap integrals. The framework simultaneously reproduces several independent experimental SRC observables, including proton--proton to proton--neutron pair ratios, relative SRC pair abundances, and proton and neutron high-momentum double ratios. A comparison between relativistic and Skyrme-type EDF families demonstrates the sensitivity of these observables to the underlying density geometry and allows the effect of the complete density profiles to be distinguished from simple radius-based geometrical estimates. Applied to neutron-rich oxygen isotopes, the framework predicts a pronounced evolution of the neutron--neutron pair abundance. Comparison with an independent calculation based on occupied harmonic-oscillator wave functions and an explicit finite-distance criterion supports the predicted isotopic evolution in neutron-rich oxygen isotopes. This agreement identifies the proton--proton to neutron--neutron SRC pair ratio as a promising experimental probe of neutron-skin thicknesses in neutron-rich nuclei and, through their connection to the symmetry energy, of the nuclear equation of state.
nucl-th
04
Wigner and mirror correlations in nuclear mass predictions with kernel ridge regression
X. H. Wu
Wigner- and mirror-correlated kernel ridge regression (WKRR) and its odd-even extension WKRRoe are developed to improve nuclear mass predictions. The Wigner and mirror correlations are encoded entirely in the kernel functions without introducing more weight parameters. For experimentally known nuclear masses, WKRRoe achieves a leave-one-out root-mean-square deviation of 98.0 keV, which falls below the often-quoted 100-keV scale discussed in connection with chaos-related limits. The gain is mainly concentrated in light nuclei near $N = Z$ and is especially large for mirror pairs. Further tests show that WKRRoe can potentially improve predictions for experimentally unknown nuclei near $N = Z$ , particularly when their mirror partners have already been measured.
nucl-thnucl-ex
05
Probing hydrodynamics in graphene and quark matter via Seebeck coefficient
Subhalaxmi Nayak · Jayanta Dey · Sabyasachi Ghosh
We investigate the Seebeck coefficient as a probe of collective transport behavior in graphene and quark-gluon plasma using a kinetic-theory approach in the hydrodynamic regime. The Seebeck coefficient is obtained by solving the Boltzmann transport equation in the relaxation-time approximation. At high-charge-carrier density, corresponding to the Fermi-liquid domain, our result approaches the behavior expected from the conventional Mott relation. In contrast, significant deviations from the Mott relation are observed in the low-carrier-density regime, corresponding to the Dirac fluid domain. These facts are in good agreement with experimental Seebeck coefficient data for graphene. This behavior indicates the emergence of collective hydrodynamic transport in graphene. The enthalpy per particle plays a key role for the Seebeck coefficient in the Dirac fluid regime. We extend our formalism to the ultra-relativistic quark-gluon plasma. A similar deviation from the Mott relation is observed, supporting a similar fluid response in the Seebeck coefficient across two markedly different strongly correlated quantum systems - graphene and quark matter.
↳ cond-mat.mes-hallnucl-th
06
Infrared Subtraction with Artificial Intelligence
Wenjie He · Xiaohui Liu · Yandong Liu · Zhan Wang
We present AI-developed local infrared subtraction, building on projection to Born and EFT matching. The framework separates an integrable radiation term from a finite contribution at Born kinematics, referred to as the Born contact. The contact is determined using the EFT singular distribution in a resolution observable such as N-jettiness $τ_{N}$ . Under human physics guidance, an LLM develops two implementations. One uses a neural network for phase space projection and fits the contact by matching to EFT cumulants. The other uses an analytic construction that keeps the Born momenta fixed while integrating over radiation. It combines the EFT $δ (τ_{N})$ coefficient with finite 4-dimensional radiation integrals to calculate the contact term directly. This gives a local subtraction formula without a slicing parameter, while reusing existing lower-order radiation calculations and EFT singular predictions. As a demonstration, we reconstruct the full NLO correction for massless 3- and 4-jet production in electron-positron annihilation. The attempt to the NNLO dijet production is also made by recursively using the NLO P2B construction with the LLM designing machine-learning controls to reduce the variance of the contact integral. The tested predictions are in good agreement with EERAD3. The numerical calculation and projection-network training use a 2020 Apple M1 MacBook, without GPU acceleration, illustrating the feasibility of the construction with modest computing resources. The appendices develop an extension of the local subtraction to 3-jet NNLO, giving explicit radiation maps and a proposed contact formula. We also show how to integrate over NNLO radiation while keeping the Born momenta fixed, for any number of massless final-state jets. Our results demonstrate how AI can help higher-order calculations by constructing infrared subtraction and improving its numerical integration.
↳ hep-phcs.AIhep-exnucl-ex+1
07
A parameter independent analysis of the QCD chiral phase transition and its universal critical behaviour
Jishnu Goswami · Frithjof Karsch · Sabarnya Mitra · Christian Schmidt
We make use of unique properties of scaling functions to estimate the chiral phase transition temperature and corresponding universal critical parameters of this phase transition directly from (2+1)-flavor QCD simulations with highly improved staggered fermions on lattices with temporal extent $N_{τ} = 8$ . Working with an improved chiral order parameter for quantifying chiral symmetry breaking, we analyze the finite-volume dependence of this observable for a wide range of lattice volumes and light quark masses, and quantitatively estimate the deviations from the expected universal scaling behaviour as a function of the light-to-strange quark mass ratio.
↳ hep-lathep-phhep-thnucl-ex+1
08
What We Have Learned from NICER About Neutron Star Radii
M. C. Miller
The cores of neutron stars have a combination of density, temperature, and neutron-proton asymmetry that cannot be replicated in laboratories or understood using first-principles quantum chromodynamics. Thus, observations of neutron stars are necessary to understand this regime. In particular, precise and accurate measurements of neutron star radii are highly informative about cold, catalyzed matter at a few times nuclear saturation density. X-ray observations with NASA's Neutron star Interior Composition Explorer (NICER) have yielded radius measurements for a few nonaccreting neutron stars, which have advanced substantially our understanding of dense matter. In this review we discuss the NICER radius measurements and their implications and demonstrate that the systematic errors thus far explored in NICER analyses have at most a minor effect on the inferred radii of neutron stars.
↳ astro-ph.HEnucl-th
09
Artificial versus Natural Atoms: The uncanny capability of the many-body Schrödinger equation to produce emergent behavior
Constantine Yannouleas
The paper reviews the theoretical and experimental progress achieved in the last 25 years in understanding the novel physics of artificial atoms and molecules as arising from the formation of Wigner molecules (WMs) of localized (to a stronger or lesser extent) fermionic or bosonic particles, which are finite quantum analogs of the more familiar bulk Wigner crystal. The term artificial atoms, as used here, encompasses a broad range of recently fabricated quantum nanodevices and experimental apparatuses consisting of a finite number of mutually repelling confined particles, including two-dimensional semiconductor and moiré transition metal dichalcogenide quantum dots, as well as trapped ultracold neutral atoms or ions. These nano-sized or micro-sized artificial devices and apparatuses (in single well or multi-well of variable-shape arrangements) hold a great promise for technological applications in the field of quantum information and quantum computers, as well as for advances in fundamental many-body physics. Prominent quantum effects of Wigner molecularization are the strong quenching of the spectral energy gaps, the appearance of rovibational spectra (in analogy with natural molecules), entanglement, and pinning due to an external perturbation. In high magnetic fields or at rapid rotation, WMs provide an alternative theory to the fractional quantum Hall effect. The physics of Wigner molecules is shown to derive from the solutions of the many-body Schrödinger equation (MBSE) in the regime of strong interparticle correlations arising from the dominance of the potential over the kinetic energy, or from a high magnetic field, as well as from a rapid rotation... (continues in the paper).
↳ cond-mat.str-elnucl-thphysics.atom-phJ. Phys.: Condens. Matter 38, 343002 (202…
10
Vector Meson Dominance and Vector Meson Production
Craig D. Roberts
Against a background supported by the three pillars of emergent mass, this contribution challenges the fidelity of vector meson dominance as an instrument for relating the electromagnetic vector-meson (V) production reaction $e + p \to e^{'} + V + p$ to the hadronic process $V + p \to V + p$ . It also describes a viable reaction model for exclusive photoproduction of light and heavy vector mesons from the proton, which exposes the $q q ˉ$ content of the photon. That model's successes reveal that it is premature to link extant $V + p \to V + p$ data with, for instance, in-proton gluon distributions, the QCD trace anomaly, or pentaquark production. Improved reaction theory and more precise data are required before the validity of such links can objectively be assessed.
↳ hep-phhep-exhep-latnucl-ex+1