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  • Open Access

(3+1)D event-by-event preequilibrium dynamics in heavy-ion collisions

Xiaojian Du1,2,3,4,5, Sören Schlichting6, and Jie Zhu6,7,*

  • *Contact author: jzhu@physik.uni-bielefeld.de
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Phys. Rev. D 113, 096009 – Published 11 May, 2026

DOI: https://doi.org/10.1103/hpzj-xx3h

Abstract

So far a major source of uncertainty in the study of heavy-ion collisions arises from the early time dynamics which includes initial state and preequilibrium dynamics. The state-of-the-art framework, KøMPøST [Kurkela et al. Phys. Rev. C 99, 034910 (2019); Kurkela et al. Phys. Rev. Lett. 122, 122302 (2019)], employs nonequilibrium Green’s functions to propagate the initial energy-momentum tensor to the hydrodynamic phase, yet currently only treats transverse plane dynamics under boost-invariant conditions. In this work, we extend KøMPøST to include nonboost-invariant responses to initial conditions, essential for accurately capturing the longitudinal structures observed in heavy-ion collisions. Nonboost-invariant fluctuations on top of a homogeneous background are evolved using (3+1)D response functions calculated in kinetic theory. To assess kinetic theory’s transition towards hydrodynamic evolution, we systematically compare the out-of-equilibrium shear-stress tensor from KøMPøST-3D with estimates based on Navier-Stokes hydrodynamics. Subsequently, a comprehensive (3+1)D framework, mcdipper + KøMPøST-3D + CLVisc + SMASH, is utilized to simulate the complete spacetime evolution of heavy-ion collisions. The sensitivity of key observables, including longitudinal structure of anisotropic flow, to variations in the hydrodynamic initialization time is thoroughly investigated.

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Phys. Rev. D 113, 096009– Published 11 May, 2026
  • Received 18 December 2025
  • Accepted 17 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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