“…The gauge field is set to zero, A t = 0, and the physical Hilbert space is obtained by acting traces of products of scalars X M (M = 1, 2, · · · , 9) on the vacuum state. 4 When we follow the usual D-brane effective theory point of view [11], the diagonal components X M,ii are regarded as the position of i-th D0-brane in R 9 , and the off-diagonal components X M,ij describe open strings connecting i-th and j-th D0-branes. Note that these strings are oriented.…”