Regularized $ζ_Δ(1)$ for polyhedra (2502.03351v1)

Abstract: Let $X$ be a compact polyhedral surface (a compact Riemann surface with flat conformal metric $\mathfrak{T}$ having conical singularities). The zeta-function $\zeta_\Delta(s)$ of the Friedrichs Laplacian on $X$ is meromorphic in ${\mathbb C}$ with only (simple) pole at $s=1$. We define ${\it reg\,}\zeta_\Delta(1)$ as $$\lim\limits_{s\to 1} \left( \zeta_\Delta(s)-\frac{ {\rm Area\,}(X,\mathfrak{T}) }{4\pi(s-1)}\right).$$ We derive an explicit expression for this spectral invariant through the holomorphic invariants of the Riemann surface $X$ and the (generalized) divisor of the conical points of the metric $\mathfrak{T}$. We study the asymptotics of ${\it reg\,}\zeta_\Delta(1)$ for the polyhedron obtained by sewing two other polyhedra along segments of small length. In addition, we calculate ${\it reg\,}\zeta(1)$ for a family of (non-Friedrichs) self-adjoint extensions of the Laplacian on the tetrahedron with all the conical angles equal to $\pi$.