The Lorentz force between D 0 and D 6 branes in string and M ( atrix ) theory ∗

We use different techniques to analyze the system formed by a D0 brane and a D6 brane (with background gauge fields) in relative motion. In particular, using the closed string formalism of boosted boundary states, we show the presence of a term linear in the velocity, corresponding to the Lorentz force experienced by the D0 brane moving in the magnetic background produced by the D6 brane. This term, that was missed in previous analyses of this system, comes entirely from the R-R odd spin structure and is also reproduced by a M(atrix) theory calculation. Work partially supported by the European Commission TMR programme ERBFMRX-CT960045 in which R.R. is associated to Torino University, and by MURST. e-mail: [email protected]