arXiv subjects

Simon F. Ross

Publications and source records attributed to Simon F. Ross.

At least 73 records · Page 4Linked to original sources

arXiv2007

Geometry of non-supersymmetric three-charge bound states

We study the smooth non-supersymmetric three-charge microstates of Jejjala, Madden, Ross and Titchener [hep-th/0504181] using Kaluza-Klein reductions of the solutions to five and four dimensions. Our aim is to improve our understanding of the relation between these non-supersymmetric solutions and the well-studied supersymmetric cases. We find some surprising qualitative differences. In the five-dimensional description, the solution has orbifold fixed points which break supersymmetry locally, so the geometries cannot be thought of as made up of separate half-BPS centers. In the four-dimensional description, the two singularities in the geometry are connected by a conical singularity, which makes it impossible to treat them independently and assign unambiguous brane charges to these centers.

hep-th↗

arXiv2007

Reversing Renormalization-Group Flows with AdS/CFT

For scalar fields in AdS with masses slightly above the Breitenlohner-Freedman bound, appropriate non-local boundary conditions can define a unitary theory. Such boundary conditions correspond to non-local deformations of the dual CFT, and generate a non-local renormalization-group flow. Nevertheless, a bulk analysis suggests that certain such flows lead to local CFTs in the infra-red. Since the flows are non-local, they can either increase or decrease the central charge of the CFT. In fact, given any local renormalization-group flow within a certain general class which leads from a UV theory (CFT_1) to an IR theory (CFT_2), we show that one can find such a non-local flow in which the endpoints are interchanged: the non-local theory flows from CFT_2 in the IR to CFT_1 in the UV. We work at large N, but the flows we consider involve quantum field effects in the bulk, corresponding to 1/N corrections in the dual theory.

hep-th↗

arXiv2006

Non-supersymmetric asymptotically AdS_5 x S^5 smooth geometries

We find soliton solutions in five-dimensional gauged supergravity, where a circle degenerates smoothly in the core of the geometry. In the family of solutions we consider, we find no completely smooth supersymmetric solutions, but we find discrete families of non-supersymmetric solitons. We discuss the relation to previous studies of the asymptotically flat case. We also consider gauged supergravities in four and seven dimensions, but fail to find any smooth solutions.

hep-th↗

arXiv2005

Winding tachyons in asymptotically supersymmetric black strings

We show that in the D1-D5 system with angular momentum, there can be localised tachyonic winding string modes in the interior of the spacetime even if we choose a spin structure which preserves supersymmetry in the asymptotic region. We consider cases where the tachyonic region extends outside the event horizon, and argue that the natural endstate of tachyon condensation in almost all cases is one of the solitonic solutions which correspond to special microstates of the D1-D5 system.

hep-th↗

arXiv2005

Causal structures and holography

We explore the description of bulk causal structure in a dual field theory. We observe that in the spacetime dual to a spacelike non-commutative field theory, the causal structure in the boundary directions is modified asymptotically. We propose that this modification is described in the dual theory by a modification of the micro-causal light cone. Previous studies of this micro-causal light cone for spacelike non-commutativite field theories agree with the expectations from the bulk spacetime. We describe the spacetime dual to field theories with lightlike non-commutativity, and show that they generically have a drastic modification of the light cone in the bulk: the spacetime is non-distinguishing. This means that the spacetime while being devoid of closed timelike or null curves, has causal curves that are ``almost closed''. We go on to show that the micro-causal light cone in the field theory agrees with this prediction from the bulk.

hep-th↗

arXiv2005

Non-supersymmetric smooth geometries and D1-D5-P bound states

We construct smooth non-supersymmetric soliton solutions with D1-brane, D5-brane and momentum charges in type IIB supergravity compactified on T^4 x S^1, with the charges along the compact directions. This generalises previous studies of smooth supersymmetric solutions. The solutions are obtained by considering a known family of U(1) x U(1) 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.

hep-th↗

arXiv2005

Smeared D0 charge and the Gubser-Mitra conjecture

We relate a Dp or NS-brane with D0-brane charge smeared over its worldvolume to the system with no D0-charge. This allows us to generalise Reall's partial proof of the Gubser-Mitra conjecture. We show explicitly for specific examples that the dynamical instability coincides with thermodynamic instability in the ensemble where the D0-brane charge can vary. We also comment on consistency checks of the conjecture for more complicated systems, using the example of the D4 with F1 and D0 charges smeared on its worldvolume.

hep-th↗

arXiv2005

Causally pathological spacetimes are physically relevant

We argue that in the context of string theory, the usual restriction to globally hyperbolic spacetimes should be considerably relaxed. We exhibit an example of a spacetime which only satisfies the causal condition, and so is arbitrarily close to admitting closed causal curves, but which has a well-behaved dual description, free of paradoxes.

gr-qc↗

arXiv2005

Black hole thermodynamics

These notes introduce basic aspects of black hole thermodynamics. I review the classical laws of black hole mechanics, give a brief introduction to the essential concepts of quantum field theory in curved spacetime, and derive the Unruh and Hawking effects. I conclude with a discussion of entropy from the Euclidean path integral point of view and in the context of the AdS/CFT correspondence. Originally delivered as a set of lectures at the PIMS summer school ``Strings, Gravity and Cosmology'' in August 2004.

hep-th↗

arXiv2004

On Gauss-Bonnet black hole entropy

We investigate the entropy of black holes in Gauss-Bonnet and Lovelock gravity using the Noether charge approach, in which the entropy is given as the integral of a suitable (n-2) form charge over the event horizon. We compare the results to those obtained in other approaches. We also comment on the appearance of negative entropies in some cases, and show that there is an additive ambiguity in the definition of the entropy which can be appropriately chosen to avoid this problem.

gr-qc↗

arXiv2004

On uniqueness of charged Kerr-AdS black holes in five dimensions

We show that the solutions describing charged rotating black holes in five-dimensional gauged supergravities found recently by Cvetic, Lu and Pope [hep-th/0406196,hep-th/0407058] 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.

hep-th↗

arXiv2004

Time-dependent spacetimes in AdS/CFT: Bubble and black hole

We extend the study of time-dependent backgrounds in the AdS/CFT correspondence by examining the relation between bulk and boundary for the smooth 'bubble of nothing' solution and for the locally AdS black hole which has the same asymptotic geometry. These solutions are asymptotically locally AdS, with a conformal boundary conformal to de Sitter space cross a circle. We study the cosmological horizons and relate their thermodynamics in the bulk and boundary. We consider the alpha-vacuum ambiguity associated with the de Sitter space, and find that only the Euclidean vacuum is well-defined on the black hole solution. We argue that this selects the Euclidean vacuum as the preferred state in the dual strongly coupled CFT.

hep-th↗

arXiv2004

Quotients of anti-de Sitter space

We study the quotients of n+1-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 n \geq 2. There are two special classes which appear in higher dimensions: one for n \geq 3 and one for n \geq 4. The description of the quotient in the majority of cases is thus a simple generalisation of the AdS_3 quotients.

hep-th↗

arXiv2004

Quotients of AdS_{p+1} x S^q: causally well-behaved spaces and black holes

Starting from the recent classification of quotients of Freund--Rubin backgrounds in string theory of the type AdS_{p+1} x S^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 and of Godel-type universes.

hep-th↗

arXiv2004

Smeared branes and the Gubser-Mitra conjecture

We show that smeared brane solutions, where a charged black p-brane is smeared uniformly over one of the transverse directions, can have a Gregory-Laflamme type dynamical instability in the smeared direction even when the solution is locally thermodynamically stable. These thus provide counterexamples to the Gubser-Mitra conjecture, which links local dynamical and thermodynamic stability. The existence of a dynamical instability is demonstrated by exploiting an ansatz due to Harmark and Obers, which relates charged solutions to neutral ones.

hep-th↗

arXiv2003

Enhancon Solutions: Pushing Supergravity to its Limits

We extend the investigation of nonextremal enhancons, 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 generalises a previous nonextreme extension of the enhancon, producing solutions with shells which satisfy the weak energy condition. We argue that identifying a unique solution with a shell requires input beyond supergravity.

hep-th↗

arXiv2003

Causal inheritance in plane wave quotients

We investigate the appearance of closed timelike curves in quotients of plane waves along spacelike isometries. First we formulate a necessary and sufficient condition for a quotient of a general spacetime to preserve stable causality. We explicitly show that the plane waves are stably causal; in passing, we observe that some pp-waves are not even distinguishing. We then consider the classification of all quotients of the maximally supersymmetric ten-dimensional plane wave under a spacelike isometry, and show that the quotient will lead to closed timelike curves iff the isometry involves a translation along the u direction. The appearance of these closed timelike curves is thus connected to the special properties of the light cones in plane wave spacetimes. We show that all other quotients preserve stable causality.

hep-th↗

arXiv2003

Properties of non-extremal enhancons

We study the supergravity solutions describing non-extremal enhancons. There are two branches of solutions: a `shell branch' connected to the extremal solution, and a `horizon branch' which connects to the Schwarzschild black hole at large mass. We show that the shell branch solutions violate the weak energy condition, and are hence unphysical. We investigate linearized perturbations of the horizon branch and the extremal solution numerically, completing an investigation initiated in a previous paper. We show that these solutions are stable against the perturbations we consider. This provides further evidence that these latter supergravity solutions are capturing some of the true physics of the enhancon.

hep-th↗