01412nas a2200145   4500008004100000245004500041210004100086260001300127520099200140100002001132700002301152700002401175700001601199856005101215       2014                        en  d00aThe stringy instanton partition function0 astringy instanton partition function  bSpringer3 aWe perform an exact computation of the gauged linear sigma model associated
to a D1-D5 brane system on a resolved A_1 singularity. This is accomplished via
supersymmetric localization on the blown-up two-sphere. We show that in the
blow-down limit C^2/Z_2 the partition function reduces to the Nekrasov
partition function evaluating the equivariant volume of the instanton moduli
space. For finite radius we obtain a tower of world-sheet instanton
corrections, that we identify with the equivariant Gromov-Witten invariants of
the ADHM moduli space. We show that these corrections can be encoded in a
deformation of the Seiberg-Witten prepotential. From the mathematical
viewpoint, the D1-D5 system under study displays a twofold nature: the
D1-branes viewpoint captures the equivariant quantum cohomology of the ADHM
instanton moduli space in the Givental formalism, and the D5-branes viewpoint
is related to higher rank equivariant Donaldson-Thomas invariants of P^1 x C^2.1 aBonelli, Giulio1 aSciarappa, Antonio1 aTanzini, Alessandro1 aVasko, Petr  uhttp://urania.sissa.it/xmlui/handle/1963/34589