Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We construct smooth nonsupersymmetric soliton solutions with D1-brane, D5-brane, and momentum charges in type IIB supergravity compactified on T 4 S 1 , with the charges along the compact directions. This generalizes previous studies of smooth supersymmetric solutions. The solutions are obtained by considering a known family of U1 U1 invariant metrics, and studying the conditions imposed by requiring smoothness. We discuss the relation of our solutions to states in the CFT describing the D1-D5 system and describe various interesting features of the geometry.

Starting from the recent classification of quotients of Freund-Rubin backgrounds in string theory of the type AdS pϩ1 ϫS q by one-parameter subgroups of isometries, we investigate the physical interpretation of the associated quotients by discrete cyclic subgroups. We establish which quotients have well-behaved causal structures, and of those containing closed timelike curves, which have interpretations as black holes. We explain the relation to previous investigations of quotients of asymptotically flat spacetimes and plane waves, of black holes in AdS spacetimes, and of Gödel-type universes.

We show that the solutions describing charged rotating black holes in fivedimensional gauged supergravities found recently by Cvetič, Lü and Pope [1,2] are completely specified by the mass, charges and angular momentum. The additional parameter appearing in these solutions is removed by a coordinate transformation and redefinition of parameters. Thus, the apparent hair in these solutions is unphysical.

We study the quotients of (nϩ1)-dimensional anti-de Sitter space by one-parameter subgroups of its isometry group SO(2,n) for general n. We classify the different quotients up to conjugation by O(2,n). We find that the majority of the classes exist for all nу2. There are two special classes which appear in higher dimensions: one for nу3 and one for nу4. The description of the quotient in the majority of cases is thus a simple generalization of the AdS 3 quotients.The study of the propagation of strings on more general curved backgrounds is important both because it allows us to confront some of the important problems arising in any theory of quantum gravity ͑such as the problem of time͒, and because describing strings on time-dependent backgrounds is essential to address the phenomenological application of string theory to cosmology. A new class of simple supersymmetric backgrounds referred to as null branes was recently constructed ͓1͔, by considering a novel class of Kaluza-Klein reductions of flat space. These do not have a timelike Killing field, so they provide interesting examples for studying string theory on more general backgrounds; in addition, a subclass of ''parabolic orbifolds'' have initial singularities. String theory on these backgrounds has been intensively studied, to expand our understanding of string theory in non-static backgrounds and to attempt to gain insight into the resolution of such spacetime singularities in string theory ͓2-4͔. Unfortunately, unlike in more familiar spacelike orbifolds, it turns out that the singular geometries suffer from an instability, so the resolution of the singularities is not accessible in perturbation theory ͓3-6͔.It is natural for many reasons to wish to extend these investigations to consider strings on orbifolds of anti-de Sitter space ͑AdS͒. First, AdS is also a maximally symmetric space, so it has a large isometry group which can lead to interesting examples of quotients. Second, the AdS conformal field theory correspondence ͓7,8͔ provides a nonperturbative definition of string theory, which may enable us to obtain more insight into issues such as singularity resolution in an AdS context. Finally, it is well known that a black hole geometry can be constructed from a quotient of AdS 3 ͓9,10͔. These constructions therefore also offer an opportunity to explore backgrounds with non-trivial causal structure.Such an extension was initiated in ͓11͔, where an AdS version of the isometry involved in the null brane quotient was constructed. Our aim in the present paper is to make a more systematic investigation of this question, classifying all the physically distinct quotients of AdS nϩ1 by one-parameter subgroups of its isometry group. The classification of quotients of AdS 3 was thoroughly explored in ͓12͔. This was extended to AdS 4 in ͓13͔. Our aim is to extend this to general dimensions, and in particular to address the case of AdS 5 , of great interest for string theory. This question has also been explored independently by Figueroa-O'Farrill and Simon ͓14...

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