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N=2 string amplitudes and the Omega background

We review recent work [1, 2] on obtaining a realisation of the $Ω$-background in terms of a special series of higher-derivative generalised F-terms in the effective $\mathcal{N}=2$ supergravity action. We discuss the motivation behind the identification of these couplings, their relation to the Nekrasov partition function and connect them to a worldsheet approach towards the refined topological string. Presented by the authors at the Corfu Summer Institute 2013 "Workshop on Noncommutative Field Theory and Gravity", September 8-15, 2013 Corfu, Greece