Quantum K-theory of incidence varieties

We prove a conjecture of Buch and Mihalcea in the case of the incidence variety X=Fl0.55542pt(1,n-1;n) X = Fl ( 1 , n - 1 ; n ) and determine the structure of its ( T -equivariant) quantum K -theory ring. Our results are an interplay between geometry and combinatorics. The geometric side concerns Gromov–Witten varieties of 3-pointed genus 0 stable maps to X with markings sent to Schubert varieties, while on the combinatorial side are formulas for the (equivariant) quantum K -theory ring of X . We prove that the Gromov–Witten variety is rationally connected when one of the defining Schubert varieties is a divisor and another is a point. This implies that the (equivariant) K -theoretic Gromov–Witten invariants defined by two Schubert classes and a Schubert divisor class can be computed in the ordinary (equivariant) K -theory ring of X . We derive a positive Chevalley formula for the equivariant quantum K -theory ring of X and a positive closed formula for Littlewood–Richardson coefficients in the non-equivariant quantum K -theory ring of X . The Littlewood–Richardson rule in turn implies that non-empty Gromov–Witten varieties given by Schubert varieties in general position have arithmetic genus 0.