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Moduli space dynamics of multi-D-vortices from D2${bar {rm D}}$ (equivalently, parallel straight D-strings from D3${bar {rm D}}$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${}^{circ}$ scattering or 0${}^{circ}$ scattering equivalent to 180${}^{circ}$ 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.
We investigate the BPS configuration of the multi D-vortices produced from the D2${bar {rm D}}$2 system. Based on the DBI-type action with a Gaussian-type runaway potential for a complex tachyon field, the BPS limit is achieved when the tachyon profi
We derive the BPS mass formulae of the Dirichlet branes from the Born-Infeld type action. BPS saturation is realized when the brane has the minimal volume while keeping the appropriate winding numbers. We apply the idea to two cases, type IIA superst
We study the gauge and gravitational interactions of the stable non-BPS D-particles of the type I string theory. The gravitational interactions are obtained using the boundary state formalism while the SO(32) gauge interactions are determined by eval
We review the boundary state description of the non-BPS D-branes in the type I string theory and show that the only stable configurations are the D-particle and the D-instanton. We also compute the gauge and gravitational interactions of the non-BPS
We use the boundary state formalism to study, from the closed string point of view, superpositions of branes and anti-branes which are relevant in some non-perturbative string dualities. Treating the tachyon instability of these systems as proposed b