ABSORPTION OF FIXED SCALARS AND THE D-BRANE APPROACH TO BLACK-HOLES

We calculate the emission and absorption rates of fixed scalars by the near-extremal five-dimensional black holes that have recently been mo deled using intersecting D-branes. We find agreement between the semi- classical and D-brane computations, At low energies the fixed scalar a bsorption cross section is smaller than for ordinary scalars and depen ds on other properties of the black hole than just the horizon area. I n the D-brane description, fixed scalar absorption is suppressed becau se these scalars must split into at least four, rather than two, open strings running along the D-brane, Consequently, this comparison provi des a more sensitive test of the effective string picture of the D-bra ne bound state than does the cross section for ordinary scalars. In pa rticular, it allows us to read off the value of the effective string t ension, That value is precisely what is needed to reproduce the near-e xtremal 5-brane entropy. (C) 1997 Published by Elsevier Science B.V.