Unstable instantons in A-model localization

We apply localization techniques to A-twisted $N$ = (2) theories of vector multiplets on S 2. We derive formulae for A-model partition functions and correlators as integrals along a real contour, as opposed to a complex one. Using the correlator formula, we successfully recover the unstable instanton partition function of pure two-dimensional Yang-Mills theory from the vacuum expectation value of an A-model operator.