ONE-LOOP VACUUM AMPLITUDE FOR D-BRANES IN CONSTANT ELECTROMAGNETIC-FIELD

Following Polchinski's approach we calculate the one-loop vacuum ampli tude for two parallel D-branes connected by open bosonic (neutral or c harged) string in a constant uniform electromagnetic (EM) field. For n eutral string, an external EM field contribution appears as a multipli er (Born-Infeld type action) of the vacuum amplitude without external EM field. Hence, this gives an alternative way to see the inducing of Born-Infeld type action for the description of D-branes. For charged s tring the situation is more complicated, and may indicate the necessit y to modify the induced D-branes action in this case.