Shear viscosity and hierarchical structure of matter Daichi Kagamihara, Munekazu Horikoshi, Chiho Nonaka, Yoji Ohashi and Kenta Shigaki Eur. Phys. J. A, 61 7 (2025) 180 Published online: 31 July 2025 DOI: 10.1140/epja/s10050-025-01653-y