Cohomological Hall algebras for Higgs torsion sheaves, moduli of triples and sheaves on surfaces

Abstract: For any free oriented Borel-Moore homology theory $A$, we construct an associative product on the $A$-theory of the stack of Higgs torsion sheaves over a projective curve $C$. We show that the resulting algebra $A\mathbf{Ha}_C^0$ admits a natural shuffle presentation, and prove it is faithful when $A$ is replaced with usual Borel-Moore homology groups. We also introduce moduli spaces of stable triples, heavily inspired by Nakajima quiver varieties, whose $A$-theory admits an $A\mathbf{Ha}_C^0$-action. These triples can be interpreted as certain sheaves on $\mathbb P(T^*C)$. In particular, we obtain an action of $A\mathbf{Ha}_C^0$ on the cohomology of Hilbert schemes of points on $T^*C$.