Nuclear Theory·nucl-th

Monday·March 16, 2026

10 papers—3 primary·7 cross-listed

04
[Submitted on 12 Mar 2026] (cross-list from hep-ph)
Elliptic Anisotropy from Quantum Diffraction
Erik Carrió🇪🇸 · Daniel Pablos🇪🇸
The surprising manifestation of collectivity in small collision systems, such as nucleon-nucleon and nucleon-nucleus collisions, is perhaps even more striking when discussed at higher momenta. In larger systems, high- $p_{T}$ elliptic anisotropy is understood as a selection bias effect due to the smaller energy loss experienced along the shorter direction that aligns with the event plane. However, in small systems the amount of energy loss appears insufficient to reproduce the sizable angular anisotropy observed experimentally. In this work, we explore a new mechanism generating preferred orientations for energetic particles without the need of energy loss. We exploit a simple model that is based on two basic although inalienable ingredients: geometry and quantum mechanics. Our findings suggest that this sum-over-paths mechanism can provide a relevant contribution to so-called flow coefficients of energetic particles traversing deconfined media of any size.
Comments:
12 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2603.12346 [pdf]
PRD(2026)·5 citations
05
[Submitted on 12 Mar 2026] (cross-list from hep-lat)
Binding energy of the $T_{bb}$ tetraquark from lattice QCD with relativistic and nonrelativistic heavy-quark actions
Jakob Hoffmann🇩🇪 · Stefan Meinel🇺🇸
We present a new determination of the $b ˉ b ˉ u d$ ( $J^{P} = 1^{+}$ , $I = 0$ ) tetraquark binding energy using lattice QCD with domain-wall light quarks and a nonperturbatively tuned three-parameter anisotropic-clover ``relativistic'' action for the $b$ quarks. We also perform a direct comparison with a reanalysis of data generated in prior work using a lattice-NRQCD action for the $b$ quarks and otherwise identical parameters. Using the new data with relativistic $b$ quarks from seven different ensembles with multiple lattice spacings and pion masses, we perform combined chiral and continuum extrapolations and obtain $(m_{T_{bb}} - m_{B} - m_{B^{*}})_{RHQ} = (- 76 \pm 23)$ MeV. For the NRQCD data from five ensembles, we perform chiral-only extrapolations and obtain $(m_{T_{bb}} - m_{B} - m_{B^{*}})_{NRQCD} = (- 74 \pm 17 \pm 10)$ MeV. The lower magnitude of the results obtained here, compared to the original analysis in Phys. Rev. D 100, 014503 (2019), is due to the use of the symmetric parts of the correlation matrices with local four-quark operators only.
Comments:
21 pages, 12 figures. v3: corrected minor error in numerical analysis; new appendix on kinetic masses; accepted by PRD
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2603.12418 [pdf]
PRD(2026)·0 citations
06
[Submitted on 13 Mar 2026] (cross-list from hep-ph)
Quarkonium spectra with magnetically induced anisotropic confinement
Ahmad Jafar Arifi🇯🇵 · Kei Suzuki🇯🇵
Strong magnetic fields modify the force that confines quarks inside hadrons and make it direction-dependent. Using quark-antiquark potentials obtained from lattice simulations as inputs to a quark potential model, we investigate how the anisotropic confinement affects the mass spectrum of quarkonium. In the strong-field regime, we find downward mass shifts induced by a softening of the confining potential along the field direction. In particular, the mass shifts of radially excited states are more significant than that of the ground state. For the longitudinal spin eigenstates, the excited-state spectrum strongly depends on the magnetic-field strength, in contrast to the spectrum with conventional isotropic confinement, which is insensitive to the field strength. This provides a clean probe of magnetically induced confinement anisotropy that can be confirmed in future lattice simulations.
Comments:
8 pages, 3 figures, and 1 table. The anisotropy parameterization has been revised
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2603.12589 [pdf]
PRD(2026)·1 citation
07
[Submitted on 13 Mar 2026] (cross-list from astro-ph.HE)
Slowly Rotating Two-Fluid Neutron Stars: Coupled Frame-Dragging, Inertia Splitting, and Universal Relations
Ankit Kumar · Hajime Sotani
We develop a fully relativistic framework to study the rotational response of gravitationally coupled two-fluid neutron stars within the slow-rotation approximation. Treating the two components as independently conserved perfect fluids interacting only through spacetime curvature, we derive the coupled equilibrium and frame-dragging equations and exploit their linear structure to construct a basis decomposition of the rotational response. This formulation leads to a natural definition of the effective total moment of inertia, which generalizes the single-fluid concept and depends solely on the equilibrium background. It further reveals that the coupled system admits two intrinsic collective rotational eigenmodes, characterized by distinct eigen-moments of inertia, even in the absence of relative rotation between the fluids. Applying this framework to neutron stars containing dark matter, we explore how the presence of an additional gravitationally bound component modifies the global rotational response and its relation to tidal deformability. Our results demonstrate that the persistence or breakdown of rotational-tidal universality in two-fluid neutron stars is governed by dark-sector microphysics rather than by the mere presence of an additional component, and establish a unified framework for interpreting rotational observables, intrinsic mode structure, and universal relations in multi-component relativistic stars.
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2603.12613 [pdf]
PRD(2026)·4 citations
08
[Submitted on 13 Mar 2026] (cross-list from hep-ph)
Probing the chiral and $U (1)$ axial symmetry restoration via meson susceptibilities in holographic QCD
Hiwa A. Ahmed🇮🇶 · Danning Li🇨🇳 · Mamiya Kawaguchi🇺🇸 · Mei Huang🇨🇳
We investigate the restoration patterns of chiral and $U (1)$ axial symmetries at finite temperature using a soft-wall holographic QCD model. The study employs two distinct parameter sets (Case I and Case II), both calibrated to reproduce a pseudocritical temperature $T_{pc} \sim 155$ MeV and the physical pion mass. The temperature dependence of the light and strange quark condensates confirms a smooth chiral crossover transition, with pseudocritical temperatures of $T_{pc} = 0.157$ GeV and $T_{pc} = 0.154$ GeV for Cases I and II, respectively. The screening masses of chiral partner mesons ( $π$ - $σ$ and $η$ - $a_{0}$ ) become degenerate near $T_{pc}$ , providing a clear signature of chiral symmetry restoration. Analysis of the corresponding meson susceptibilities further supports this conclusion. However, the indicator for $U (1)$ axial symmetry restoration, $χ_{π} - χ_{a_{0}}$ , vanishes at a temperature $T \sim 0.190$ GeV, which indicates a distinct restoration scale with chiral symmetry restoration scale within the present holographic framework. The temperature-dependent topological susceptibility $χ_{top}^{1/4}$ is also computed, showing a sharp drop near $T_{pc}$ and a subsequent slight decrease. While the model qualitatively captures established features of the chiral transition, the results highlight a limitation in the qualitative description of the $U (1)$ axial anomaly compared to LQCD in our work.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2603.12911 [pdf]
PRD(2026)·1 citation
09
[Submitted on 13 Mar 2026] (cross-list from nucl-ex)
$π$ , K, and p production in high-multiplicity pp collisions at $s = 13$ TeV
ALICE Collaboration
This paper presents the measurement of $π^{\pm}$ , K $^{\pm}$ , and p( $p ˉ$ ) production in high-multiplicity proton-proton collisions at $s = 13$ TeV at midrapidity ( $∣ y ∣ < 0.5$ ) using the ALICE detector at the LHC. The transverse-momentum ( $p_{T}$ ) spectra of these particles are reported for three high-multiplicity classes. The results show a mass- and multiplicity-dependent hardening of the $p_{T}$ spectra and an enhancement of the p/ $π$ ratio at intermediate $p_{T}$ . These features are similar to those observed in heavy-ion collisions, where quark-gluon plasma formation is expected. The new measurements have extended the highest average charged-particle multiplicity density per unit of pseudorapidity achieved in pp collisions, roughly a factor five higher than that in average inelastic pp collisions, thereby reducing the multiplicity gap between small and large collision systems. In addition, the results are further compared with previously published measurements and with model calculations obtained using distinct tunes of the PYTHIA 8 Monte Carlo generator, as well as with predictions from the EPOS4. The comparison of the $p_{T}$ -integrated K/ $π$ and p/ $π$ ratios across different collision systems and energies suggests that particle production scales with charged-particle multiplicity, rather than with collision energy or system size. While the PYTHIA 8 tunes and the EPOS4 model are able to reproduce some of these measurements, either quantitatively or qualitatively, none of them consistently describes all observed features of the data.
Comments:
24 pages, 7 captioned figures, 3 tables, authors from page 19, submitted to EPJC, figures at http://alice-publications.web.cern.ch/node/13158
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2603.13203 [pdf]
0 citations
10
[Submitted on 13 Mar 2026] (cross-list from nucl-ex)
Measurement of correlations between elliptic flow and mean transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
ALICE Collaboration
Measurements of the event-by-event correlation between elliptic flow ( $v_{2}$ ) and the mean transverse momentum ( $[p_{T}]$ ) using the modified Pearson correlation coefficient $ρ (v_{2}^{2}, [p_{T}])$ are reported in pp collisions at $s = 13$ TeV, and in p-Pb and Pb-Pb collisions at a center-of-mass energy per nucleon pair $s_{NN} = 5.02$ TeV. This analysis is based on the full LHC Run 2 dataset recorded by ALICE and is performed for the first time in small collision systems with the ALICE detector. In Pb-Pb collisions, the $ρ (v_{2}^{2}, [p_{T}])$ measurement shows a non-monotonic dependence on charged particle multiplicity ( $N_{ch}$ ); it first decreases and then increases with an increase in multiplicity. The decreasing trends of $ρ (v_{2}^{2}, [p_{T}])$ with increasing multiplicity are also observed in p-Pb and pp collisions for the presented multiplicity range. All three systems show consistent values of $ρ (v_{2}^{2}, [p_{T}])$ for $N_{ch} ≲ 80$ . These measurements are also compared with theoretical model calculations, including PYTHIA, where no collectivity is generated, as well as AMPT and IP-Glasma + MUSIC + UrQMD, which produce collective effects in small systems. These comparisons offer unique insights into the origin of collectivity in small systems. They improve the understanding of the initial geometry, size, and their correlations. The comparison also allows an investigation of the role of initial momentum correlations predicted by the Color Glass Condensate framework. The new measurements could not be explained by current state-of-the-art models, offering insights into the initial stage of collisions in small systems and also imposing strong constraints on the existing theoretical models. This will significantly advance our understanding of the collective phenomena observed in small systems at the LHC.
Comments:
21 pages, 5 captioned figures, authors from page 16, submitted to JHEP, figures at http://alice-publications.web.cern.ch/node/13159
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2603.13217 [pdf]
2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Elliptic Anisotropy from Quantum Diffraction

Binding energy of the Tbb​ tetraquark from lattice QCD with relativistic and nonrelativistic heavy-quark actions

Quarkonium spectra with magnetically induced anisotropic confinement

Slowly Rotating Two-Fluid Neutron Stars: Coupled Frame-Dragging, Inertia Splitting, and Universal Relations

Probing the chiral and U(1) axial symmetry restoration via meson susceptibilities in holographic QCD

π, K, and p production in high-multiplicity pp collisions at s​=13 TeV

Measurement of correlations between elliptic flow and mean transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC

Affiliations

Binding energy of the $T_{bb}$ tetraquark from lattice QCD with relativistic and nonrelativistic heavy-quark actions

Probing the chiral and $U (1)$ axial symmetry restoration via meson susceptibilities in holographic QCD

$π$ , K, and p production in high-multiplicity pp collisions at $s = 13$ TeV