October 1987
Author:
Scott A. Yost
Comments: 93 pgs
Reference: Princeton University Dissertation, October 1987
This thesis investigates the extension of background field techniques in string theory to include string loop effects. First, beta function methods are used to find the equations of motion for a gauge field coupled to the boundary of a worldsheet. The dependence of the gauge field beta function on both the open and closed string massless backgrounds is obtained in this manner. Then, we discuss the background field dependence of the one-loop open string vacuum amplitudes. This calculation is done using both path-integral methods and the operator formalism. Next, the effect of a boundary on the closed string beta functions is derived. This is the simplest case of a string loop correction to the beta functions. The calculation requires an analysis of the divergences of vacuum amplitudes occurring when the boundary shrinks to a point. It is possible to obtain an effective action for the open and closed string modes which incorporates the loop corrections. Finally, the cancellation of tadpoles between graphs of different order in the string loop expansion is analyzed using the operator formalism.