Topological Background Fields as Quantum Degrees of Freedom of   Compactified Strings
  It is shown that background fields of a topological character usually introduced as such in compactified string theories correspond to quantum degrees of freedom which parametrise the freedom in choosing a representation of the zero mode quantum algebra in the presence of non-trivial topology. One consequence would appear to be that the values of such quantum degrees of freedom, in other words of the associated topological background fields, cannot be determined by the nonperturbative string dynamics. 
Jan Govaerts and Florian Payen (CP3, UCL, Louvain-la-Neuve, Belgium)