We show that if $\lbrace \varphi_i\rbrace_{ i\in \Gamma}$ and $\lbrace \psi_j\rbrace_{ j\in\Lambda}$ are self-affine iterated function systems on the plane that satisfy strong separation, domination and irreducibility, then for any associated self-affine measures $\mu$ and $\nu$, the inequality $$\dim_{ \rm H}(\mu*\nu) < \min \lbrace 2, \dim_{ \rm H} \mu + \dim_{ \rm H} \nu \rbrace$$ implies that there is algebraic resonance between the eigenvalues of the linear parts of $\varphi_i$ and $\psi_j$. This extends to planar non-conformal setting the existing analogous results for self-conformal measures on the line.
Categories: math.CA math.DS