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Equivariant Cohomology Of The Chiral de Rham Complex And The Half-Twisted Gauged Sigma Model

In this paper, we study the perturbative aspects of the half-twisted variant of Witten's topological A-model coupled to a non-dynamical gauge field with Kahler target space X being a G-manifold. Our main objective is to furnish a purely physical interpretation of the equivariant cohomology of the chiral de Rham complex, recently constructed by Lian and Linshaw in [arXiv:math/0501084], called the "chiral equivariant cohomology". In doing so, one finds that key mathematical results such as the vanishing in the chiral equivariant cohomology of positive weight classes, lend themselves to straightforward physical explanations. In addition, one can also construct topological invariants of X from the correlation functions of the relevant physical operators corresponding to the non-vanishing weight-zero classes. Via the topological invariance of these correlation functions, one can verify, from a purely physical perspective, the mathematical isomorphism between the weight-zero subspace of the chiral equivariant cohomology and the classical equivariant cohomology of X. Last but not least, one can also determine fully, the de Rham cohomology ring of X/G, from the topological chiral ring generated by the local ground operators of the physical model under study.