Consistency Conditions for Orientifolds and D-Manifolds

TL;DR

This paper investigates the consistency conditions for superstring theories with orientifold projections and D-branes, revealing implications for gauge groups and conformal field theories in specific compactifications.

Contribution

It identifies two key consistency conditions for orientifold and D-brane setups and explores their implications for gauge groups and conformal theories in Type I string models.

Findings

Type I theory's D5-branes have symplectic gauge groups.

Constructed consistent Type I models on K3/Z2 orbifolds with various gauge subgroups.

Linked K3 orbifold with embedded spin connection to an interacting conformal field theory.

Abstract

We study superstrings with orientifold projections and with generalized open string boundary conditions (D-branes). We find two types of consistency condition, one related to the algebra of Chan-Paton factors and the other to cancellation of divergences. One consequence is that the Dirichlet 5-branes of the Type I theory carry a symplectic gauge group, as required by string duality. As another application we study the Type I theory on a $K3$ $Z_2$ orbifold, finding a family of consistent theories with various unitary and symplectic subgroups of $U(16) \times U(16)$. We argue that the $K3$ orbifold with spin connection embedded in gauge connection corresponds to an interacting conformal field theory in the Type I theory.