Introduction

In this chapter we start to consider the properties of the massless relativistic string (the MRS). We will begin with a simple situation in which the MRS plays the role of a constant force field, acting upon a ‘charge’ and an ‘anticharge’ placed at the endpoints of an open MRS. This means that the motion will be in one space dimension along the force direction. We will refer to it as the yoyo-mode for reasons that will become clear when it is exhibited.

In later chapters we will come back to more complex modes involving several dimensions. All these modes are used in the Lund model as semi-classical models for different high-energy interactions between hadrons. The yoyo-mode is used both to describe an e+e– annihilation event and as a simple model for stable hadrons. In the last section of this chapter we provide a possible dynamical analogy between the QCD vacuum and superconductivity as a justification for using string dynamics to describe hadronic states and interactions.

In the yoyo-mode the two charges at the endpoints of the string move like point particles, i.e. the momentum of the state is localised in these endpoint particles of the MRS force field. At any moment the total energy of the state can be decomposed into the energy in the force field, corresponding to a linearly rising potential, and the kinetic energies of the particles at the endpoints.