• DOI:10.1103/PhysRevLett.128.122302
• Corpus ID: 239009442

Hydrodynamic Gradient Expansion Diverges beyond Bjorken Flow.

@article{Heller2022HydrodynamicGE,
  title={Hydrodynamic Gradient Expansion Diverges beyond Bjorken Flow.},
  author={Michal P. Heller and Alexandre Serantes and Michal Spali'nski and Viktor Svensson and Benjamin Withers},
  journal={Physical review letters},
  year={2022},
  volume={128 12},
  pages={
          122302
        }
}

• M. Heller, Alexandre Serantes, +2 authors Benjamin Withers
• Published 14 October 2021
• Physics
• Physical review letters

The gradient expansion is the fundamental organizing principle underlying relativistic hydrodynamics, yet understanding its convergence properties for general nonlinear flows has posed a major challenge. We introduce a simple method to address this question in a class of fluids modeled by Israel-Stewart-type relaxation equations. We apply it to (1+1)-dimensional flows and provide numerical evidence for factorially divergent gradient expansions. This generalizes results previously only obtained for (0+1)-dimensional comoving flows, notably Bjorken flow. We also demonstrate that the only known nontrivial case of a convergent hydrodynamic gradient expansion at the nonlinear level relies on Bjorken flow symmetries and becomes factorially divergent as soon as these are relaxed. Finally, we show that factorial divergence can be removed using a momentum space cutoff, which generalizes a result obtained earlier in the context of linear response.