The Nambu-Goto theory of closed bosonic strings moving in 1 + 3–dimensional Minkowski space: the construction of the quantum algebra of observables up to degree five

The quantum algebra of observables of closed bosonic strings moving in 1 + 3–dimensional Minkowski space is constructed up to degree five. All independent relations of degree four are computed; they involve three as yet undetermined parameters. Definitions and symbols are used as introduced in the above-mentioned article.