Dimension of the Green measure of skew products with dominant exponent in the fibers

Abstract

Let $f(z,w)=(p(z),q(z,w))$ be a polynomial skew product of $\mathbb{C}^2$ of degree $d\geqslant 2$ and let $μ$ and $μ_p$ be the Green measures associated to $f$ and $p$ respectively. Let $λ_1 > λ_2$ and $λ_p$ be the Lyapunov exponents of $(f,μ)$ and $(p,μ_p)$ respectively. We show that if $λ_2 = λ_p$, then $μ$ is exact dimensional and: \begin{equation*}\dim_Hμ=\frac{\log d}{λ_1}+\frac{\log d}{λ_2}.\end{equation*} The proof relies on the continuity of the conditional measures obtained by Jonsson, on the fact that $μ$ has constant Jacobian $d^2$, and on a fibered version of a normal form theorem for the inverse branches of the iterates of $f$.