Unstable instantons in A-model localization

We apply localization techniques to A-twisted $\mathcal{N}$ \( \mathcal{N} \) = (2) theories of vector multiplets on S². 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.