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@ARTICLE{Chatagnon:1050465,
      author       = {Chatagnon, Thomas and Chraibi, Mohcine and Pettré, Julien
                      and Seyfried, Armin and Tordeux, Antoine},
      title        = {{W}hen legs and bodies synchronize: {T}wo-level collective
                      dynamics in dense crowds},
      publisher    = {arXiv},
      reportid     = {FZJ-2026-00234},
      year         = {2026},
      abstract     = {Ultra-dense crowds, in which physical contact between
                      people cannot be avoided, pose major safety concerns.
                      Nevertheless, the underlying dynamics driving their
                      collective behaviours remain poorly understood. Existing
                      dense crowd models, mostly two-dimensional and
                      contact-based, overlook biomechanical mechanisms that govern
                      individual balance motion. In this study, we introduce a
                      minimal two-level pedestrian model that couples upper body
                      and legs dynamics, allowing us to capture transitions
                      between balanced and unbalanced states at the individual
                      scale. Whereas previous models fail to achieve it, this
                      coupling gives rise to emergent collective behaviours
                      observed empirically, such as self-organized waves and
                      large-scale rotational motion within the crowd. The model
                      bridges basic individual biomechanical concepts and
                      macroscopic flow dynamics, offering a new framework for
                      modelling and understanding collective motions in
                      ultra-dense crowds.},
      keywords     = {Physics and Society (physics.soc-ph) (Other) / FOS:
                      Physical sciences (Other)},
      cin          = {IAS-7},
      cid          = {I:(DE-Juel1)IAS-7-20180321},
      pnm          = {5111 - Domain-Specific Simulation $\&$ Data Life Cycle Labs
                      (SDLs) and Research Groups (POF4-511)},
      pid          = {G:(DE-HGF)POF4-5111},
      typ          = {PUB:(DE-HGF)25},
      doi          = {10.48550/ARXIV.2601.05867},
      url          = {https://juser.fz-juelich.de/record/1050465},
}