Exotic $\mathbb{R}^4$'s, RBG Links, and End Floer Homology

We give the first pair of non-diffeomorphic exotic $\mathbb{R}^4$'s made by attaching diffeomorphic Casson handles onto diffeomorphic disk complements. Our examples are obtained using the RBG link construction to find slice knots with diffeomorphic slice disk complements, but whose Whitehead doubled disk complements are not diffeomorphic. We distinguish the exotic $\mathbb{R}^4$'s using end Floer homology.