arXiv subjects

Keith Copsey

Publications and source records attributed to Keith Copsey.

14 recordsLinked to original sources

arXiv2013

The instability of orientifolds and the end of the (string) landscape as we know it

Negative mass brane-like objects known as orientifolds are crucial in the construction of all presently understood realistic string compactifications and I review in general the link between negative energy objects and the existence of a landscape of metastable vacua. While in string perturbation theory these solutions are non-dynamical, and hence avoid the usual instabilities of negative tension objects, beyond perturbation theory it is well known that one may lift orientifolds in M-theory to solutions well described by classical general relativity and which consequently may be distorted in a variety of ways. I review the failure of the usual positive energy theorems, as well as several supersymmetric stability arguments, in this context and demonstrate that one may smoothly distort the lifted orientifold, preserving the boundary conditions, into solutions of lower energy. I present significant (numerical) evidence that solutions with arbitrarily negative energy may be found among these distorted orientifolds. Consequently, I suggest that this instability is a fatal one and hence there is little reason to believe in the existence of a string theory landscape. I briefly comment on the implications for Type I string theory and string dualities.

hep-th↗

arXiv2012

Singularities in Hyperscaling Violating Spacetimes

We examine spacetimes which generalize Lifshitz scaling to allow hyperscaling violation invariance (i.e. a constant conformal transformation) for the types of singularities frequently found in the Lifshitz case. We find that most of these spacetimes suffer either from a traditional naked curvature singularity or a null curvature singularity robust against stringy higher derivative corrections. We do find a one-parameter family that evades these issues but this family requires exotic matter, in particular involving a negative energy density that may not be interpreted as due to a cosmological constant.

hep-th↗

arXiv2011

Hidden singularities and closed timelike curves in a proposed dual for Lifshitz-Chern-Simons gauge theories

We point out that the metrics recently proposed by K. Balasubramanian and J. McGreevy \cite{BalaMcGreevyLifshitz} as gravitational duals to Lifshitz Chern-Simons gauge theories contain both a hidden null singularity and a region of closed timelike curves accessible to asymptotic observers. Like the singularity in the original Liftshitz spacetime given by Kachru, Liu, and Mulligan, this singularity does not include large $α'$ or $g_s$ corrections and hence appears to be singular in string theory as well as classically.

hep-th↗

arXiv2011

Coleman-de Luccia reconsidered: a subtlety of gravity and the thin wall approximation

I point out that the usual Coleman-de Luccia analysis of tunnelling via instantons between perturbatively stable minima using the thin-wall approximation misses one of the effects of gravitational backreaction on the on-shell action and hence the decay rate. Once this oversight is corrected, one finds these decay rates are much larger than has been generally appreciated; including the effects of gravity potentials involving barriers which are relatively high and not overly wide result in decays which are quite rapid instead of slow. In the light of these results, it is no longer clear that one should believe string theory predicts a wide class of cosmologically long-lived metastable de Sitter vacua.

hep-th↗

arXiv2011

Gravitation and tunnelling: Subtleties of the thin-wall approximation and rapid decays

I provide some simple physical arguments that, once gravitation and some subtleties are taken into account, rather broad classes of potentials result in instantons which tunnel relatively rapidly between perturbatively stable minima. In particular, due to some previously unappreciated technical subtleties, the decay rates for instantons which may be well-described as thin-wall are much larger than the usual Coleman-de Luccia result. I discuss with some level of rigor when the thin-wall approximation holds and clarify some misconceptions regarding the application of this approximation and its meaning. I also point out potentials involving small differences between the maxima and minima generically decay relatively rapidly. These two classes of potentials include those usually used to argue for the existence of a string landscape and in light of these results it is not clear that de Sitter vacua presently understood will generically be cosmologically long-lived.

gr-qc↗

arXiv2011

Pathologies in Asymptotically Lifshitz Spacetimes

There has been significant interest in the last several years in studying possible gravitational duals, known as Lifshitz spacetimes, to anisotropically scaling field theories by adding matter to distort the asymptotics of an AdS spacetime. We point out that putative ground state for the most heavily studied example of such a spacetime, that with a flat spatial section, suffers from a naked singularity and further point out this singularity is not resolvable by any known stringy effect. We review the reasons one might worry that asymptotically Lifshitz spacetimes are unstable and employ the initial data problem to study the stability of such systems. Rather surprisingly this question, and even the initial value problem itself, for these spacetimes turns out to generically not be well-posed. A generic normalizable state will evolve in such a way to violate Lifshitz asymptotics in finite time. Conversely, enforcing the desired asymptotics at all times puts strong restrictions not just on the metric and fields in the asymptotic region but in the deep interior as well. Generically, even perturbations of the matter field of compact support are not compatible with the desired asymptotics.

hep-th↗

arXiv2010

New instabilities of de Sitter spacetimes

We construct an instanton describing the pair production of non-Kaluza Klein bubbles of nothing in higher odd dimensional de Sitter spaces. In addition to showing that higher dimensional de Sitter spaces have a nonzero probability to become topologically nontrivial, this process provides direct evidence for the association of entropy with cosmological horizons and that non-Kaluza Klein bubbles of nothing are a necessary ingredient in string theory or any other consistent quantum theory of gravity in higher dimensions.

gr-qc↗

arXiv2009

Solitons in Five Dimensional Minimal Supergravity: Local Charge, Exotic Ergoregions, and Violations of the BPS Bound

We describe a number of striking features of a class of smooth solitons in gauged and ungauged minimal supergravity in five dimensions. The solitons are globally asymptotically flat or asymptotically AdS without any Kaluza-Klein directions but contain a minimal sphere formed when a cycle pinches off in the interior of the spacetime. The solutions carry a local magnetic charge and many have rather unusual ergosurfaces. Perhaps most strikingly, many of the solitons have more electric charge or, in the asymptotically AdS case, more electric charge and angular momentum than is allowed by the usual BPS bound. We comment on, but do not resolve, the new puzzle this raises for AdS/CFT.

hep-th↗

arXiv2008

States of Negative Energy and $AdS_5 \times S_5/Z_k$

We develop a careful definition of energy for nonsupersymmetric warped product asymptotically $AdS_d \times M_q$ solutions which include a nonzero p-form. In the case of an electric p-form extending along all the AdS directions, and in particular in the case of self-dual fields like those used in the Freund-Rubin construction, the Hamiltonian is well defined only if a particular asymptotic gauge for the p-form is used. Rather surprisingly, asymptotically this gauge is time dependent, despite the fact the field and metric are not. We then consider a freely orbifolded $AdS_5 \times S_5$ and demonstrate that the standard boundary conditions allow states of arbitrarily negative energy. The states consist of time symmetric initial data describing bubbles that are regular up to singularities due to smeared D3-branes. We discuss the evolution of this data and point out that if the usual boundary conditions are enforced such bubbles may never reach infinity.

hep-th↗

arXiv2007

Bubbles Unbound II: AdS and the Single Bubble

I present further analytic time symmetric initial data for five dimensions describing ``bubbles of nothing'' which have no Kaluza-Klein circle asymptotically. The new solutions consist of a large family of single bubbles in both asymptotically flat and asymptotically AdS space. I also numerically construct gravitational solitons in AdS where the usual boundary conditions are modified geometrically but not topologically. Furthermore I point out there are both regular AdS bubbles and topologically trivial metrics in asymptotically global AdS dual to matter which violates all the usual energy conditions, both classical and quantum. I inquire as to the existence of a dual gravitational instability.

hep-th↗

arXiv2007

Bubbles Unbound: Bubbles of Nothing Without Kaluza-Klein

I present analytic time symmetric initial data for five dimensions describing ``bubbles of nothing'' which are asymptotically flat in the higher dimensional sense, i.e. there is no Kaluza-Klein circle asymptotically. The mass and size of these bubbles may be chosen arbitrarily and in particular the solutions contain bubbles of any size which are arbitrarily light. This suggests the solutions may be important phenomenologically and in particular I show that at low energy there are bubbles which expand outwards, suggesting a new possible instability in higher dimensions. Further, one may find bubbles of any size where the only region of high curvature is confined to an arbitrarily small volume.

hep-th↗

arXiv2006

Gravity Dual of Gauge Theory on S^2 x S^1 x R

We (numerically) construct new static, asymptotically AdS solutions where the conformal infinity is the product of time and S^2 x S^1. There always exist a family of solutions in which the S^1 is not contractible and, for small S^1, there are two additional families of solutions in which the S^1 smoothly pinches off. This shows that (when fermions are antiperiodic around the S^1) there is a quantum phase transition in the gauge theory as one decreases the radius of the S^1 relative to the S^2. We also compare the masses of our solutions and argue that the one with lowest mass should minimize the energy among all solutions with conformal boundary S^2 x S^1 x R. This provides a new positive energy conjecture for asymptotically locally AdS metrics. A simple analytic continuation produces AdS black holes with topology S^2 x S^1.

hep-th↗

arXiv2005

The Role of Dipole Charges in Black Hole Thermodynamics

Modern derivations of the first law of black holes appear to show that the only charges that arise are monopole charges that can be obtained by surface integrals at infinity. However, the recently discovered five dimensional black ring solutions empirically satisfy a first law in which dipole charges appear. We resolve this contradiction and derive a general form of the first law for black rings. Dipole charges do appear together with a corresponding potential. We also include theories with Chern-Simons terms and generalize the first law to other horizon topologies and more generic local charges.

hep-th↗

arXiv2004

Through the Looking Glass: AdS-FT with time dependent boundary conditions and black hole formation

I solve for the behavior of scalars in Lorentzian AdS with time dependent boundary conditions, focusing in particular on the dilaton. This corresponds, via the AdS-CFT correspondence, to considering a gauge theory with a time dependent coupling. Changes which keep the gauge coupling nonzero result in finite but physically interesting states in the bulk, including black holes, while sending the gauge coupling to zero appears to produce a cosmological singularity in the bulk.

hep-th↗