NO-FORCE CONDITION AND BPS COMBINATIONS OF P-BRANES IN 11 AND 10 DIMENSIONS

The condition of vanishing of the static force on a q-brane probe in t he gravitational background produced by another p-brane is used to giv e a simple derivation of the pair-wise intersection rules which govern the construction of BPS combinations of branes. These rules, while im plied also by supersymmetry considerations, thus have a purely bosonic origin. Imposing the no-force requirement makes it possible to add br anes 'one by one' to construct composite BPS configurations (with zero binding energy) of 2-branes and 5-branes in D = 11 and of various p-b ranes in D = 10. The advantage of this elementary approach is its univ ersality, i.e. the cases of different dimensions and different types o f branes (e.g., NS-NS, R-R and 'mixed' combinations of NS-NS and R-R b ranes in D = 10) are all treated in the same way.