Stable non-BPS D-branes of type I

We review the boundary state description of the non-BPS D-branes in the typeI string theory and show that the only stable configurations are the D-particleand the D-instanton. We also compute the gauge and gravitational interactionsof the non-BPS D-particles and compare them with the interactions of the dualnon-BPS particles of the heterotic string finding complete agreement. In thisway we provide further dynamical evidence of the heterotic/type I duality