The cohomology of general tensor products of vector bundles on the projective plane (2008.10695v2)

Abstract: Computing the cohomology of the tensor product of two vector bundles is central in the study of their moduli spaces and in applications to representation theory, combinatorics and physics. These computations play a fundamental role in the construction of Brill-Noether loci, birational geometry and $S$-duality. Using recent advances in the Minimal Model Program for moduli spaces of sheaves on $\mathbb{P}^2$, we compute the cohomology of the tensor product of general semistable bundles on $\mathbb{P}^2$. This solves a natural higher rank generalization of the polynomial interpolation problem. More precisely, let $v$ and $w$ be two Chern characters of stable bundles on $\mathbb{P}^2$ and assume that $w$ is sufficiently divisible depending on $v$. Let $V \in M(v)$ and $W \in M(w)$ be two general stable bundles. We fully compute the cohomology of $V \otimes W$. In particular, we show that if $W$ is exceptional, then $V \otimes W$ has at most one nonzero cohomology group determined by the slope and the Euler characteristic, generalizing foundational results of Dr\'{e}zet, G\"{o}ttsche and Hirschowitz. We characterize the invariants of effective Brill-Noether divisors on $M(v)$. We also characterize when $V\otimes W$ is globally generated. Our computation is canonical given the birational geometry of the moduli space, suggesting a roadmap for tackling analogous problems on other surfaces.