Dynamics of (n,1) strings

An (n,1) string is a bound state of a D-string and n fundamental strings. It may be described by a D-string with a world volume electric field turned on. As the electric field approaches its critical value, n becomes large. We calculate the 4-point function for transverse oscillations of an (n,1) string, and the two-point function for massless closed strings scattering off an (n,1) string. In both cases we find a set of poles that becomes dense in the large n limit. The effective tension that governs the spacing of these poles is the fundamental string tension divided by 1+(nλ)2, where λ is the closed string coupling. We associate this effective tension with the open strings attached to the (n,1) string, thereby governing its dynamics. We also argue that the effective coupling strenth of these open strings is reduced by the electric field and approaches zero in the large n limit.