An induction theorem for groups acting on trees

Abstract:

If $G$ is a group acting on a locally finite tree $X$, and $\mathscr {S}$ is a $G$-equivariant sheaf of vector spaces on $X$, then its compactly-supported cohomology is a representation of $G$. Under a finiteness hypothesis, we prove that if $H_c^0(X, \mathscr {S})$ is an irreducible representation of $G$, then $H_c^0(X, \mathscr {S})$ arises by induction from a vertex or edge stabilizing subgroup.

If $\boldsymbol {\mathrm {G}}$ is a reductive group over a nonarchimedean local field $F$, then Schneider and Stuhler realize every irreducible supercuspidal representation of $G = \boldsymbol {\mathrm {G}}(F)$ in the degree-zero cohomology of a $G$-equivariant sheaf on its reduced Bruhat-Tits building $X$. When the derived subgroup of $\boldsymbol {\mathrm {G}}$ has relative rank one, $X$ is a tree. An immediate consequence is that every such irreducible supercuspidal representation arises by induction from a compact-mod-center open subgroup.