From diffeomorphisms to exotic phenomena in small 4-manifolds

We provide an approach to study exotic phenomena in relatively small 4-manifolds that captures many different exotic behaviors under one umbrella. These phenomena include exotic smooth structures on 4-manifolds with $b_2=1$, examples of strong corks, and exotic codimension-$1$ embeddings into $\mathbb{C} P^2 \# - \mathbb{C} P^2$ that survive external stabilization. We also give a new way to detect a homeomorphism of a 4-manifold that is not topologically isotopic to any diffeomorphism and give lower bounds of relative genera of certain knots. Our primary tools are constraints on diffeomorphisms of 4-manifolds obtained from families Seiberg-Witten theory.