Conformal measures of (anti)holomorphic correspondences

In this paper, we study the existence and properties of conformal measures on limit sets of (anti)holomorphic correspondences. We show that if the critical exponent satisfies $1\le {\delta }_{\mathrm{crit}}(x)<+\mathrm{\infty },$ the correspondence $F$ is (relatively) hyperbolic on the limit set ${\mathrm{\Lambda }}_{+}(x)$, and ${\mathrm{\Lambda }}_{+}(x)$ is minimal, then ${\mathrm{\Lambda }}_{+}(x)$ admits a non-atomic conformal measure for $F$ and the Hausdorff dimension of ${\mathrm{\Lambda }}_{+}(x)$ is strictly less than 2. As a special case, this shows that for a parameter $a$ in the interior of a hyperbolic component of the modular Mandelbrot set, the limit set of the Bullett–Penrose correspondence $F_a$ has a non-atomic conformal measure and its Hausdorff dimension is strictly less than 2. The same results hold for the LLMM correspondences, under some extra assumptions on its defining function $f$.