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Nuclear Theory·nucl-th

Friday·October 31, 2025

9 papers—4 primary·5 cross-listed

All9Primary4Cross-lists5
  1. 05

    Deriving a parton shower for jet thermalization in QCD plasmas

    Ismail Soudi🇫🇮 · Adam Takacs🇩🇪

    Jet quenching - the modification of high-energy jets in the quark-gluon plasma - has been extensively studied through weakly coupled scattering amplitudes embedded in parton-shower frameworks. These models, often combined with bulk hydrodynamic evolution, successfully describe a wide range of observables, though they typically rely on assumptions of rapid thermalization and simplified treatments of medium response. Parallel to these developments, jet thermalization has been investigated within the finite-temperature QCD effective kinetic theory, which provides our best microscopic understanding of equilibration in heavy-ion collisions. Early studies of linearized perturbations have highlighted both the promise and the limitations of current approaches, as existing MC implementations face challenges - particularly in the treatment of recoils and particle merging. Building on this foundation, we introduce a new parton-shower algorithm that exactly reproduces the dynamics of the linearized EKT, enabling a first-principles description of jet thermalization with proper inclusion of recoils, holes, quantum statistics, and merging processes.

    ↳ hep-phhep-exhep-thnucl-thPRD(2026)·3 citations
  2. 06

    MC-EKRT: Monte Carlo event generator with saturated minijet production for initializing 3+1 D fluid dynamics in high energy nuclear collisions

    Harri Niemi🇫🇮 · Jussi Auvinen🇫🇮 · Kari J. Eskola🇫🇮 · Henry Hirvonen🇺🇸 · Yuuka Kanakubo🇯🇵 · Mikko Kuha🇫🇮

    We present a novel saturation and leading order collinear factorization based Monte-Carlo implementation of the EKRT model for computing QCD matter initial states in high-energy nuclear collisions. As new features the MC implementation gives a full 3-dimensional initial state event-by-event, introduces new event-by-event fluctuating spatially dependent nuclear parton distribution functions, includes dynamical fluctuations in minijet production and saturation, and accounts for the energy-momentum and valence-quark number conservation.

    ↳ hep-phnucl-thEPJ Web Conf.(2026)·0 citations
  3. 07

    Close encounters with attractors of the third kind

    Alexander Soloviev🇸🇮

    We report on the existence of a hydrodynamic attractor in the Mueller-Israel-Stewart framework of a fluid living in the novel geometry discovered recently by Grozdanov. This geometry, corresponding to a hyperbolic slicing of dS, complements previous analyses of attractors in Bjorken (flat slicing) and Gubser (spherical slicing) flows. The fluid behaves like a sharply localized droplet propagating rapidly along the lightcone. Typical solutions approach the hydrodynamic attractor rapidly at late times despite a Knudsen number exceeding unity, suggesting that the inverse Reynolds number captures hydrodynamization more faithfully since the shear stress vanishes at late times. This is in stark contrast to Gubser flow, which has both the Knudsen and inverse Reynolds number becoming small for intermediate times. We close with a comparison to Weyl-transformed Bjorken flow and discuss possible phenomenological applications.

    ↳ hep-thhep-phnucl-thPRD(2026)·3 citations
  4. 08

    Moments of parton distributions functions of the pion from lattice QCD using gradient flow

    Anthony Francis🇹🇼 · Patrick Fritzsch🇮🇪 · Rohith Karur🇺🇸 · Jangho Kim🇰🇷 · Giovanni Pederiva🇩🇪 · Dimitra A. Pefkou🇺🇸 · Antonio Rago🇩🇰 · Andrea Shindler🇺🇸 · André Walker-Loud🇺🇸 · Savvas Zafeiropoulos🇫🇷

    We present a nonperturbative determination of the pion valence parton distribution function (PDF) moment ratios up to , using the gradient flow in lattice QCD. As a testing ground, we employ SU() isosymmetric gauge configurations generated by the OpenLat initiative with a pseudoscalar mass of . Our analysis uses four lattice spacings and a nonperturbatively improved action, enabling full control over the continuum extrapolation, and the limit of vanishing flow time, . The flowed ratios exhibit O() scaling across the ensembles, and the continuum-extrapolated results, matched to the scheme at GeV using next-to-next-to-leading order matching coefficients, show only mild residual flow-time dependence. The resulting ratios, computed with a relatively small number of configurations, are consistent with phenomenological expectations for the pion's valence distribution, with statistical uncertainties that are competitive with modern global fits. These findings demonstrate that the gradient flow provides an efficient and systematically improvable method to access partonic quantities from first principles. Future extensions of this work will target lighter pion masses toward the physical point, and applications to nucleon structure such as the proton PDFs and the gluon and sea-quark distributions.

    ↳ hep-lathep-exhep-phnucl-thPRD(2026)·19 citations
  5. 09

    Determination of the initial condition for the Balitsky-Kovchegov equation with transformers

    Meisen Gao🇨🇳 · Zhong-Bo Kang🇺🇸 · Jani Penttala🇺🇸 · Ding Yu Shao🇨🇳

    In the high-energy limit of QCD, scattering off nucleons and nuclei can be described in terms of Wilson-line correlators whose energy dependence is perturbative. The energy dependence of the two-point correlator, called the dipole amplitude, is governed by the Balitsky-Kovchegov (BK) equation. The initial condition for the BK equation can be fitted to the experimental data, which requires evolving the dipole amplitude for a large set of different parameter values. In this work, we train a transformer model to learn the energy dependence of the dipole amplitude, skipping the time-consuming numerical evaluation of the BK equation. The transformer predicts the learned dipole amplitude and the leading order inclusive deep inelastic scattering cross section very accurately, allowing for efficient fitting of the initial condition to the experimental data. Using this setup, we fit the initial condition of the BK equation to the inclusive deep inelastic scattering data from HERA and consider two different starting points for the evolution. We find better agreement with the experimental data for a smaller . This work paves the way for future studies involving global fits of the dipole amplitude at leading order and beyond.

    ↳ hep-phnucl-exnucl-thJHEP(2026)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE