Phase Transitions and Non-Mainstream Norms in a Coevolution Model of Opinions and Actions with Three-Way Decision Thresholds

In social systems, the coevolution of individual opinions and external actions is fundamental to understanding collective phenomena such as group decision-making and innovation diffusion. Traditional models often simplify the opinion–action relationship into linear or probabilistic mappings, which struggle to capture the widely observed opinion–action inconsistency and nonlinear phase transitions. From the perspective of social physics, this paper integrates the threshold concept of three-way decision theory to construct an opinion–action coevolution model on a dual-layer network. The model introduces decision thresholds that divide the opinion to action process into acceptance, delay, and rejection regions, thereby quantifying decision uncertainty and providing a structured representation of the intermediate hesitation state. Through large-scale agentbased simulations, we explore the effects of mass media, innovation leaders, and the strength of opinion–action coupling on the emergence of collective social innovation. Our findings reveal three main results: (1) Media and innovation leaders exert a synergistic driving effect on innovation diffusion; (2) Excessive opinion–action coupling can trigger a negative feedback trap, whereby strong social conformity pressure suppresses rather than accelerates innovation adoption; (3) When leaders exhibit opinion–action inconsistency, the system may evolve into a stable non-mainstream norm characterized by high opinion consensus but persistently low action levels. These results offer a new mechanistic explanation for phenomena such as delayed adoption and social norm lock-in. The robustness of these findings is further confirmed across diverse network topologies, alternative opinion dynamics models, and different update protocols.