Cocompact Fuchsian groups with a modular embedding (2503.12656v2)

Abstract: A Fuchsian group $\Gamma$ has a modular embedding if its adjoint trace field is a totally real number field and every unbounded Galois conjugate $\Gamma^\sigma$ comes equipped with a holomorphic (or conjugate holomorphic) map ${\phi^\sigma : \mathbb{B}^1 \to \mathbb{B}^1}$ intertwining the actions of $\Gamma$ and $\Gamma^\sigma$ on the Poincar\'e disk $\mathbb{B}^1$. This paper provides the first cocompact nonarithmetic Fuchsian groups with a modular embedding that are not commensurable with a triangle group. The main result, proved using period domains, is that any immersed totally geodesic complex curve on a complex hyperbolic $2$-orbifold has a modular embedding. Another consequence is that there are infinitely many signatures for which no finite-volume quotient of $\mathbb{B}^1$ with that signature can be an immersed totally geodesic curve on a complex hyperbolic $2$-orbifold.