Let $K$ be a p.c.f. self-similar set equipped with a strongly recurrent Dirichlet form. Under a homogeneity assumption, for an open set $\Omega\subset K$ whose boundary $\partial \Omega$ is a graph-directed self-similar set, we prove that the eigenvalue counting function $\rho^\Omega(x)$ of the Laplacian with Dirichlet or Neumann boundary conditions (Neumann only for connected $\Omega$) has an explicit second term as $x\to +\infty$, beyond the dominant Weyl term. If $\partial\Omega$ has a strong iterated structure, we establish that \begin{ equation*} \rho^\Omega(x)=\nu(\Omega)G\Big(\frac{ \log x}2\Big)x^{ \frac{ d_S}2}+\kappa(\partial\Omega)G_1\Big(\frac{ \log x}2\Big)x^{ \frac d2}+o\big(x^{ \frac d2}\big), \end{ equation*} where $G$ and $G_1$ are bounded periodic functions, $\nu$ and $\kappa$ are certain reference measures, and $d_S$ and $d$ are dimension-related parameters.
Categories: math.FA