SCALE-INDEPENDENT SPIN EFFECTS IN D-BRANE DYNAMICS

We study spin interactions between two moving D-branes using the Green -Schwarz formalism of boundary states. We focus our attention on the l eading terms for small velocities v, of the form v(4-n)/r(7-P+n) (v(2- n)/r(3-p+n)) for p-p (p-p + 4) systems, with 16 (8) supercharges. In a nalogy with standard GS computations of massless four-point one-loop a mplitudes in Type I theory, the above terms are governed purely by zer o-modes, massive states contributions cancelling as expected by the re sidual supersymmetry. This implies the scale invariance of these leadi ng spin effects, supporting the relevant matrix model descriptions of supergravity interactions; in this context, we also discuss similar re sults for more general brane configurations. We then give a field theo ry interpretation of our results that allows us in particular to deduc e the gyromagnetic ratio g = 1 and the presence of a quadrupole moment for D0-branes. (C) 1998 Elsevier Science B.V.