Gauge symmetry in the Ramond-Ramond sector of superstring theory

We examine properties of internal gauge symmetries in string theory. In the low energy limit these symmetries are candidates to describe the strong, weak and electromagnetic interactions of elementary particles. Typically, gauge symmetries in the closed superstring are related to massless particles in the Neveu Schwarz-Neveu Schwarz (NS-NS) sector. In this dissertation gauge bosons in the Ramond-Ramond (R-R) sector of four-dimensional models based on the superstring are also analyzed. Conventionally, R-R vector bosons are abelian. We exhibit couplings for non-abelian R-R bosons at tree level. In superstring theory, the conformal fields which correspond to the ground states in the Ramond sector are spin fields. In order to compute scattering amplitudes that involve spin fields, we present the vertex operators in the covariant BRST formalism, which is based on the BRST quantization of the superstring. For the closed superstring, we explicitly construct bi-spinor states, i.e. we express the tensor product of two spinors in terms of Pauli matrices. Then using trace identities we compute spinor expressions that arise in scattering amplitudes for NS-NS and R-R states. We will also prove several identities involving polarization vectors. We discuss BRST picture changing for massless fermions and bosons and present vertex operators for Ramond-Ramond vector bosons. Modular invariance of four-dimensional models incorporating these states is discussed. Couplings involving gravitons, dilatons and gauge bosons are computed.* ftn*Please refer to the dissertation for the attached papers.