Group interactions create discontinuous phase transitions in SIS dynamics
ρ(infected): 0.000β₁: -β₂: -Step: 0
Higher-order contagion (Iacopini et al 2019): on hypergraphs with pairwise edges and triangles (3-simplices),
infection can spread via pairs (rate β₁) and via group interactions when ≥2 neighbors are infected (rate β₂).
The triangle term creates a discontinuous (first-order) phase transition and bistability —
a hallmark absent in standard SIS on graphs. The phase diagram shows the abrupt jump in endemic prevalence.