STRING IN CURVED SPACETIMES: THE NULL STRING APPROACH

The string propagation in curved spacetimes is investigated in the null string approach. In this approach the string equations of motion and constraints are systematically expanded in powers of c (the speed of light in the world-sheet). We obtain to zeroth order the null string (string with zero tension), while the first order correction incorporates the string dynamics.

We apply our formalism to null strings in de Sitter spacetime. After a reparametrization of the world-sheet coordinates, the equations of motion are solved. The quantum algebra generated by the constraints is considered, ordering the momentum operators to the right of the coordinate operators. No critical dimension appears. It is anticipated however that the conformal anomaly will appear when the first order corrections proportional to T₀, are introduced.