A note on the supergravity description of dielectric branes

We comment on the recent papers by Costa et al. and Emparan, which show how one might generate supergravity solutions describing certain dielectric branes in ton dimensions. The "basic" such solutions describe either N fundamental strings or N D4-branes expanding into a D6-brane, with topology M-2 circle times S-5 or M-5 circle times S-2 respectively. Treating these solutions in a unified way, we note that they allow for precisely two values of the radius of the relevant sphere, and that the solution with the smaller value of the radius has the lower energy. Moreover, the possible radii in both cases agree up to numerical factors with the corresponding solutions of the D6-brane worldvolume theory. We thus argue that these supergravity solutions are the correct gravitational description of the dielectric branes of Emparan and Myers. (C) 2001 Elsevier Science B.V. All rights reserved.