Creation of Fundamental Strings by Crossing Dirichlet Branes

We study the force balance between orthogonally positioned {ital p}-brane and (8{minus}p)-brane. The force due to graviton and dilaton exchange is repulsive in this case. We identify the attractive force that balances this repulsion as due to one-half of a fundamental string stretched between the branches. As the {ital p}-brane passes through the (8{minus}p)-brane, the connecting string changes direction, which may be interpreted as creation of one fundamental string. We show this directly from the structure of the Chern-Simons terms in the D-brane effective actions. We also discuss the effect of string creation on the 0-brane quantum mechanics in the type I{sup {prime}} theory. {copyright} {ital 1997} {ital The American Physical Society}