We review what has been learnt and what remains unknown about the physics of hot enhancons following studies in supergravity. We recall a rather general family of static, spherically symmetric, non-extremal enhancon solutions describing D4 branes wrapped on K3 and discuss physical aspects of the solutions. We embed these solutions in the six dimensional supergravity describing type IIA strings on K3 and generalize them to have arbitrary charge vector. This allows us to demonstrate the equivalence with a known family of hot fractional D0 brane solutions, to widen the class of solutions of this second type and to carry much of the discussion across from the D4 brane analysis. In particular we argue for the existence of a horizon branch for these branes.
In subsequent work on non-BPS , involving two of the current authors, we used simple supergravity techniques to find the most general solutions with the correct symmetries and asymptotic charges of the hot system @cite_3 . We showed that the only non-BPS solution with a well-behaved event horizon is the horizon branch.
@cite_3
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We extend the investigation of nonextremal enhan c c ons, finding the most general solutions with the correct symmetry and charges. There are two families of solutions. One of these contains a solution with a regular horizon found previously; this previous example is shown to be the unique solution with a regular horizon. The other family generalizes a previous nonextreme extension of the enhan c c on, producing solutions with shells that satisfy the weak energy condition. We argue that identifying a unique solution with a shell requires input beyond supergravity.