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 order to embed the non-extremal D4 brane solutions of @cite_3 in the six dimensional supergravity, we display a simple two charge truncation which describes the solutions studied in @cite_3 . These solutions can then be lifted straight across into the larger supergravity theory. In deriving the truncation, it is convenient to switch to heterotic variables using the well-known duality between type IIA on K3 and heterotic strings on @math . This is also convenient for comparing with the fractional brane solutions of @cite_2 since that paper presents solutions in the heterotic frame. However, we should stress that we are performing T-dualities between different IIA solutions and in principle we could have worked in IIA variables throughout.
@cite_3 @cite_2
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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. Abstract We construct non-extremal fractional D-brane solutions of type-II string theory at the Z 2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N =2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhancon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system.