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arXiv · hep-th/9406101

Gso Projection, BRST Cohomology and Picture-Changing in N=2 String Theory

J. Bischoff·S. V. Ketov·O. Lechtenfeld
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Abstract

We investigate in detail the critical $N{=}2$ fermionic string with and without a global ${\bf Z}_2$ twist. An analysis of BRST cohomology shows that twisted sectors contain massless `spacetime' fermions which are {\it non-local\/} with respect to the standard massless boson. However, two distinct GSO projections exist, one (untwisted) retaining merely the usual boson and its spectral-flow partner, the other (twisted) yielding two fermions and one boson, on the massless level. The corresponding chiral BRST-invariant vertex operators are constructed in certain pictures, and their fusion and picture-changing are investigated, including the construction of inverse picture-changing operators. The $N{=}2$ `spacetime supersymmetry' generators are {\it null\/} operators, since the twisted massless states fail to interact. The untwisted three- and four-point functions are recalculated at tree-level.

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J. Bischoff, S. V. Ketov, O. Lechtenfeld. 1994-10-05. Gso Projection, BRST Cohomology and Picture-Changing in N=2 String Theory. https://doi.org/10.1016/0550-3213(94)00536-n

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