In this chapter we construct the superstring theories in flat Minkowski spacetime. Their main advantage with respect to bosonic string theory is that they lead to spacetime fermions. In addition, they naturally lead to spacetime supersymmetry, which guarantees the absence of spacetime tachyons, and thus provide stable vacua. There are five such superstring theories, called the type IIA and IIB theories, the E8 × E8 and SO(32) heterotic theories, and type I theory, which we study in that order. These superstrings are the best studied string theories, and have been efficiently applied to the construction of realistic particle physics models, to be developed in later chapters.
4.1 Fermions on the worldsheet
We would like to construct ...