Geometric Analysis on the Diederich-Fornæss Index

Abstract

We derive a sufficient condition on a bounded pseudoconvex domain $Ω\subset\mathbb{C}^2$ with smooth boundary such that $-(-ρ)^η$ is plurisubharmonic on $Ω$ for $η>0$ arbitrarily close to $1$ (the supremum of $η$ is called Diederich-Fornæss index, see Definition (df)). This condition (see Theorem prop) extends a theorem of Fornæss and Herbig in 2007 and only requires restriction on Levi-flat sets of the boundary $\partialΩ$. Since the condition is on Levi-flat sets, it contains more geometric information. As an application of this new condition, we discuss how the geometry of the Levi-flat sets affects the Diederich-Fornæss index. Among other results, we show that the Diederich-Fornæss index is $1$ if only the Levi-flat sets form a real curve transversal to the holomorphic tangent vector fields on $\partialΩ$ (see Theorem [main]). We also give a specific example (see Theorem [example]) on the bounded pseudoconvex domains which verify the application but are neither of finite type nor admit a plurisubharmonic defining function on the boundary.