Utility Perturbation Operators in Bayesian Games: Structural Stability and Equilibrium Deformation

We introduce a class of parametric operators acting on the space of Bayesian games with continuous utility functions. Each operator induces a structured perturbation of agents’ utilities while preserving the underlying informational primitives, strategy spaces, and Bayesian updating. This construction generates a family of utility-perturbed Bayesian games that can be interpreted as continuous deformations of classical incomplete-information games in the space of payoff functions. The contribution of the paper is purely mathematical. First, we formally define a utility perturbation operator and characterize the associated class of perturbed Bayesian games. Second, under standard compactness and continuity assumptions, we prove the existence of Nash equilibria for all admissible perturbations. Third, we show that the equilibrium correspondence of the perturbed games converges upper hemicontinuously to the classical Bayesian Nash equilibrium correspondence as the perturbation parameter vanishes. Under additional differentiability and strict concavity assumptions, we establish a structural stability result: in a neighborhood of the unperturbed game, equilibria are locally unique and depend smoothly on the perturbation parameter. The equilibrium mapping is continuous, locally Lipschitz, and differentiable, implying that utility perturbations generate a stable deformation of the classical equilibrium structure rather than a qualitative departure from it. Taken together, the results identify a new operator-based framework for studying equilibrium stability and sensitivity in Bayesian games. The analysis shows that parametric perturbations of utility functions define a mathematically well-posed deformation of classical game-theoretic equilibria, providing a foundation for further work on equilibrium equivalence, stability, and comparative statics in non-cooperative games.