Relativistic dynamics of multi-BPS D-vortices and straight BPS D-strings

Moduli space dynamics of multi-D-vortices from D2D¯2 (equivalently, parallel straight D-strings from D3D¯3) is systematically studied. For the BPS D-vortices, we show through exact calculations that the classical motion of randomly-distributed n D-vortices is governed by a relativistic Lagrangian of free massive point-particles. When the head-on collision of two identical BPS D-vortices of zero radius is considered, it predicts either 90° scattering or 0° scattering equivalent to 180° scattering. Since the former leads to a reconnection of two identical D-strings and the latter does to a case of their passing through each other, two possibilities are consistent with the prediction of string theory. It is also shown that the force between two non-BPS vortices is repulsive. Although the obtained moduli space dynamics of multi-BPS-D-vortices is exact in classical regime, the quantum effect of an F-string pair production should be included in determining the probabilities of the reconnection and the passing through for fast-moving cosmic superstrings.