Hybrid universality classes of systemic cascades

Cascades are self-reinforcing processes underlying the systemic risk of many complex systems. Understanding the universal aspects of these phenomena is of fundamental interest, yet typically bound to numerical observations in ad-hoc models and limited insights. Here, we develop a unifying approach that reveals two distinct universality classes of cascades determined by the global symmetry of the cascading process. We provide hyperscaling arguments predicting hybrid critical phenomena characterized by a combination of both mean-field spinodal exponents and d-dimensional corrections, and show how parity invariance influences the geometry and lifetime of critical avalanches. Our theory applies to a wide range of networked systems in arbitrary dimensions, as we demonstrate by simulations encompassing classic and novel cascade models, revealing universal principles of cascade critical phenomena amenable to experimental validation.