Taming the supergravity description of non-BPS D-branes: the D/anti-D solution

We obtain the supergravity solution which describes a bound state ofD-string/anti-D-string pairs attached to different fixed planes of an orbifold,in type IIB string theory compactified on T^4/Z_2. For parameters at which theconformal field theory point of view predicts stability, the solution displaysa repulson-like singularity. However, we observe that a D-string/anti-D-stringpair probe in this background becomes tensionless before reaching thesingularity, suggesting a resolution by the enhancon mechanism. Moreover, theforce feels by this probe is attractive, in contrast to the repulsive behaviourobserved in the non-BPS D-brane description.Comment: 21 pages, Latex, uses JHEP.cls. Substantial revision; in particular, clarification of the two T-dual descriptions in section 2 and improved discussion of the enhancon mechanism in section 4. Published versio