Dualities in Comparison Theorems and Bundle-Valued Generalized Harmonic Forms on Noncompact Manifolds

Abstract: We observe, utilize dualities in differential equations and differential inequalities, dualities between comparison theorems in differential equations, and obtain dualities in "swapping" comparison theorems in differential equations. These dualities generate comparison theorems on differential equations of mixed types I and II and lead to comparison theorems in Riemannian geometry with analytic, geometric, P.D.E.'s and physical applications. In particular, we prove Hessian comparison theorems and Laplacian comparison theorem under varied radial Ricci curvature or radial curvature assumptions, generalizing and extending the work of Han-Li-Ren-Wei, and Wei. We also extend the notion of function or differential form growth to bundle-valued differential form growth of various types and discuss their interrelationship. These provide tools in extending the notion, integrability and decomposition of generalized harmonic forms to those of bundle-valued generalized harmonic forms, introducing Condition W for bundle-valued differential forms, and proving duality theorem and unity theorem, generalizing the work of Andreotti and Vesentini, and Wei. We then apply Hessian and Laplacian comparison theorems to obtain comparison theorems in mean curvature, generalized sharp Caffarelli-Kohn-Nirenberg type inequalities, embedding theorem for weighted Sobolev spaces, geometric differential-integral inequalities, generalized sharp Hardy type inequalities on Riemannian manifolds, monotonicity formulas and vanishing theorems for differential forms of degree $k$ with values in vector bundles, such as $F$-Yang Mills fields (when $F$ is the identity map, they are Yang-Mills fields), generalized Yang-Mills-Born-Infeld fields on manifolds, Liouville type theorems for $F$-harmonic maps, and Dirichlet problems on starlike domains for vector bundle valued differential $1$-forms and $F$-harminic maps, etc.