An introduction to string states and their interactions

TL;DR

This paper introduces the theory of string states and their interactions in open bosonic strings, emphasizing a new covariant method for constructing physical states and calculating scattering amplitudes.

Contribution

It presents a novel covariant technique for constructing infinite trajectories of string states and applies it to efficient calculation of tree-level scattering amplitudes.

Findings

New covariant method for state construction

Efficient calculation of tree-level amplitudes

Insights into string spectrum and interactions

Abstract

The subject matter of these lecture notes is the open bosonic critical string, its perturbative spectrum and interactions. We begin with a brief review of classical string propagation, quantization, as well as the level-by-level construction of physical string states. We then review a new, covariant and efficient technology of constructing entire trajectories of infinitely many physical states deeper in the string spectrum. Finally, elements of the calculation of string scattering amplitudes, including aspects of the application of the technology for the efficient calculation of tree-level amplitudes of deeper trajectories, are also covered. The material is based on three invited lectures delivered by the author at the 2024 Modave Summer School in Mathematical Physics.