Published by Institute of Physics Publishing for SISSA Received: January 17, 2008 Accepted: January 22, 2008 Published: January 28, 2008 Explaining the pure spinor formalism for the JHEP01(2008)065 superstring Nathan Berkovits Instituto de F´ısica Te´orica, State University of S˜ao Paulo, Rua Pamplona 145, 01405-900, S˜ao Paulo, SP, Brasil E-mail:
[email protected] Abstract: After adding a pair of non-minimal fields and performing a similarity trans- formation, the BRST operator in the pure spinor formalism is expressed as a conventional- looking BRST operator involving the Virasoro constraint and (b, c) ghosts, together with 12 fermionic constraints. This BRST operator can be obtained by gauge-fixing the Green- Schwarz superstring where the 8 first-class and 8 second-class Green-Schwarz constraints are combined into 12 first-class constraints. Alternatively, the pure spinor BRST opera- tor can be obtained from the RNS formalism by twisting the ten spin-half RNS fermions into five spin-one and five spin-zero fermions, and using the SO(10)/ U(5) pure spinor variables to parameterize the different ways of twisting. GSO( ) vertex operators in the − pure spinor formalism are constructed using spin fields and picture-changing operators in a manner analogous to Ramond vertex operators in the RNS formalism. Keywords: Superstrings and Heterotic Strings, Topological Strings. Contents 1. Introduction 1 2. Conventional-looking pure spinor BRST operator 4 2.1 Brief review of pure spinor formalism 4 2.2 Non-minimal fields and similarity transformation 6 JHEP01(2008)065 3. GSO(−) states in the pure spinor formalism 8 3.1 GSO(+) vertex operators 8 3.2 GSO( ) vertex operators 8 − 3.3 Picture-changing operators 9 3.4 Scattering amplitudes 10 4.