HMARL-CBF – Hierarchical Multi-Agent Reinforcement Learning with Control Barrier Functions for Safety-Critical Autonomous Systems - Ahmad, H M Sabbir; Sabouni, Ehsan; Wasilkoff, Alexander; Budhraja, Param; Guo, Zijian; Zhang, Songyuan; Fan, Chuchu; Cassandras, Christos G; Li, Wenchao (Advances in Neural Information Processing Systems, 2025)