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Robert C. Myers

Publications and source records attributed to Robert C. Myers.

At least 163 records · Page 9Linked to original sources
arXiv1999

Exact Description of Black Holes on Branes

To test recent ideas about lower dimensional gravity bound to a brane, we construct exact solutions describing black holes on two-branes in four dimensions. We find that 2+1 gravity is indeed recovered at large distances along the brane, although there are significant deviations at smaller scales. Large black holes appear as flattened "pancakes", with a relatively small extent off the brane. Black hole thermodynamics is discussed from both the standpoint of the brane and the bulk. We comment on the analogous black holes bound to higher dimensional branes.

hep-th↗
arXiv1999

The Noncommutative Bion Core

We examine noncommutative solutions of the nonabelian theory on the world-volume of N coincident D-strings. These solutions can be interpreted in terms of noncommutative geometry as funnels describing the nonabelian D-string expanding out into an orthogonal D3-brane. These configurations are `dual' to the bion solutions in the abelian world-volume theory of the D3-brane. In the latter, a charge N magnetic monopole describes N D-strings attached to the D3-brane with a spike deformation of the world-volume. The noncommutative D-string solutions give a reliable account of physics at the core of the monopole, where the bion description is expected to breakdown. In the large N limit, we find good agreement between the two points of view, including the energy, couplings to background fields, and the shape of the funnel. We also study fluctuations traveling along the D-string, again obtaining agreement in the large N limit. At finite N, our results give a limit on the number of modes that can travel to infinity along the N D-strings attached to the D3-brane.

hep-th↗
arXiv1999

Surface Terms as Counterterms in the AdS/CFT Correspondence

We examine the recently proposed technique of adding boundary counterterms to the gravitational action for spacetimes which are locally asymptotic to anti-de Sitter. In particular, we explicitly identify higher order counterterms, which allow us to consider spacetimes of dimensions d<=7. As the counterterms eliminate the need of ``background subtraction'' in calculating the action, we apply this technique to study examples where the appropriate background was ambiguous or unknown: topological black holes, Taub-NUT-AdS and Taub-Bolt-AdS. We also identify certain cases where the covariant counterterms fail to render the action finite, and we comment on the dual field theory interpretation of this result. In some examples, the case of vanishing cosmological constant may be recovered in a limit, which allows us to check results and resolve ambiguities in certain asymptotically flat spacetime computations in the literature.

hep-th↗
arXiv1999

Spin-Two Glueballs, Positive Energy Theorems and the AdS/CFT Correspondence

We determine the spectrum of graviton excitations in the background geometry of the AdS soliton in p+2 dimensions. Via the AdS/CFT correspondence this corresponds to determining the spectrum of spin two excitations in the dual effective p-dimensional field theories For the cases of D3- and M5-branes these are the spin two glueballs of QCD_3 and QCD_4 respectively. For all values of p we find an exact degeneracy of the spectra of these tensor states and certain scalar excitations. Our results also extend the perturbative proof of a positive energy conjecture for asymptotically locally AdS spacetimes (originally proposed for p=3) to an arbritrary number of dimensions.

hep-th↗
arXiv1999

The O(dd) Story of Massive Supergravity

The low energy effective action describing the standard Kaluza-Klein reduction of heterotic string theory on a d-torus possesses a manifest O(d,d+16) symmetry. We consider generalized Scherk-Schwarz reductions of the heterotic string to construct massive gauged supergravities. We show that the resulting action can still be written in a manifestly O(d,d+16) invariant form, however, the U-duality transformations also act on the mass parameters. The latter play the dual role of defining the scalar potential and the nonabelian structure constants. We conjecture that just as for the standard reduction, a subgroup of this symmetry corresponds to an exact duality symmetry of the heterotic string theory.

hep-th↗
arXiv1999

Holography, Thermodynamics and Fluctuations of Charged AdS Black Holes

The physical properties of Reissner-Nordstrom black holes in (n+1)-dimensional anti-de Sitter spacetime are related, by a holographic map, to the physics of a class of n-dimensional field theories coupled to a background global current. Motivated by that fact, and the recent observations of the striking similarity between the thermodynamic phase structure of these black holes (in the canonical ensemble) and that of the van der Waals-Maxwell liquid-gas system, we explore the physics in more detail. We study fluctuations and stability within the equilibrium thermodynamics, examining the specific heats and electrical permittivity of the holes, and consider the analogue of the Clayperon equation at the phase boundaries. Consequently, we refine the phase diagrams in the canonical and grand canonical ensembles. We study the interesting physics in the neighbourhood of the critical point in the canonical ensemble. There is a second order phase transition found there, and that region is characterized by a Landau-Ginzburg model with A_3 potential. The holographically dual field theories provide the description of the microscopic degrees of freedom which underlie all of the thermodynamics, as can be seen by examining the form of the microscopic fluctuations.

hep-th↗
arXiv1999

Stress Tensors and Casimir Energies in the AdS/CFT Correspondence

We discuss various approaches to extracting the full stress-energy tensor of the conformal field theory from the corresponding supergravity solutions, within the framework of the Maldacena conjecture. This provides a more refined probe of the AdS/CFT correspondence. We apply these techniques in considering the Casimir energy of the conformal field theory on a torus. It seems that either generically the corresponding supergravity solutions are singular (i.e., involve regions of large string-scale curvatures), or that they are largely insensitive to the boundary conditions of the CFT on the torus.

hep-th↗
arXiv1999

Charged AdS Black Holes and Catastrophic Holography

We compute the properties of a class of charged black holes in anti-de Sitter space-time, in diverse dimensions. These black holes are solutions of consistent Einstein-Maxwell truncations of gauged supergravities, which are shown to arise from the inclusion of rotation in the transverse space. We uncover rich thermodynamic phase structures for these systems, which display classic critical phenomena, including structures isomorphic to the van der Waals-Maxwell liquid-gas system. In that case, the phases are controlled by the universal `cusp' and `swallowtail' shapes familiar from catastrophe theory. All of the thermodynamics is consistent with field theory interpretations via holography, where the dual field theories can sometimes be found on the world volumes of coincident rotating branes.

hep-th↗
arXiv1998

Supersymmetry of Rotating Branes

We present a new 1/8 supersymmetric intersecting M-brane solution of D=11 supergravity with two independent rotation parameters. The metric has a non-singular event horizon and the near-horizon geometry is $adS_3\times S^3\times S^3\times\bE^2$ (just as in the non-rotating case). We also present a method of determining the isometry supergroup of supergravity solutions from the Killing spinors and use it to show that for the near horizon solution it is $D(2|1,α)\times D(2|1,α)$ where $α$ is the ratio of the two 3-sphere radii. We also consider various dimensional reductions of our solution, and the corresponding effect of these reductions on the Killing spinors and the isometry supergroups.

hep-th↗
arXiv1998

Large N Phases, Gravitational Instantons and the Nuts and Bolts of AdS Holography

Recent results in the literature concerning holography indicate that the thermodynamics of quantum gravity (at least with a negative cosmological constant) can be modeled by the large N thermodynamics of quantum field theory. We emphasize that this suggests a completely unitary evolution of processes in quantum gravity, including black hole formation and decay; and even more extreme examples involving topology change. As concrete examples which show that this correspondence holds even when the space-time is only locally asymptotically AdS, we compute the thermodynamical phase structure of the AdS-Taub-NUT and AdS-Taub-Bolt spacetimes, and compare them to a 2+1 dimensional conformal field theory (at large N) compactified on a squashed three sphere, and on the twisted plane.

hep-th↗
arXiv1998

The AdS/CFT Correspondence and a New Positive Energy Conjecture for General Relativity

We examine the AdS/CFT correspondence when the gauge theory is considered on a compactified space with supersymmetry breaking boundary conditions. We find that the corresponding supergravity solution has a negative energy, in agreement with the expected negative Casimir energy in the field theory. Stability of the gauge theory would imply that this supergravity solution has minimum energy among all solutions with the same boundary conditions. Hence we are lead to conjecture a new positive energy theorem for asymptotically locally Anti-de Sitter spacetimes. We show that the candidate minimum energy solution is stable against all quadratic fluctuations of the metric.

hep-th↗
arXiv1998

On Generalized Axion Reductions

Recently interest in using generalized reductions to construct massive supergravity theories has been revived in the context of M-theory and superstring theory. These compactifications produce mass parameters by introducing a linear dependence on internal coordinates in various axionic fields. Here we point out that by extending the form of this simple ansatz, it is always possible to introduce the various mass parameters simultaneously. This suggests that the various ``distinct'' massive supergravities in the literature should all be a part of a single massive theory.

hep-th↗
arXiv1998

Flow of low energy couplings in the Wilson renormalization group

A new form of the Wilson renormalization group equation is derived, in which the flow equations are, up to linear terms, proportional to a gradient flow. A set of coördinates is found in which the flow of marginal, low-energy, couplings takes a gradient form, if relevant couplings are tuned to vanish.

hep-th↗
arXiv1998

Cosmic Censorship: As Strong As Ever

Spacetimes which have been considered counter-examples to strong cosmic censorship are revisited. We demonstrate the classical instability of the Cauchy horizon inside charged black holes embedded in de Sitter spacetime for all values of the physical parameters. The relevant modes which maintain the instability, in the regime which was previously considered stable, originate as outgoing modes near to the black hole event horizon. This same mechanism is also relevant for the instability of Cauchy horizons in other proposed counter-examples of strong cosmic censorship.

gr-qc↗
arXiv1997

Pure states don't wear black

Recently, string theory has provided some remarkable new insights into the microphysics of black holes. I argue that a simple and important lesson is also provided with regards to the information loss paradox, namely, pure quantum states do not form black holes! Thus it seems black hole formation, as well as evaporation, must be understood within the framework of quantum decoherence.

gr-qc↗
arXiv1996

Wavy Strings: Black or Bright?

Recent developments in string theory have brought forth a considerable interest in time-dependent hair on extended objects. This novel new hair is typically characterized by a wave profile along the horizon and angular momentum quantum numbers $l,m$ in the transverse space. In this work, we present an extensive treatment of such oscillating black objects, focusing on their geometric properties. We first give a theorem of purely geometric nature, stating that such wavy hair cannot be detected by any scalar invariant built out of the curvature and/or matter fields. However, we show that the tidal forces detected by an infalling observer diverge at the `horizon' of a black string superposed with a vibration in any mode with $l \ge 1$. The same argument applied to longitudinal ($l=0$) waves detects only finite tidal forces. We also provide an example with a manifestly smooth metric, proving that at least a certain class of these longitudinal waves have regular horizons.

hep-th↗
arXiv1996

Aspects of Type IIB Theory on ALE Spaces

D-brane technology and strong/weak coupling duality supplement traditional orbifold techniques by making certain background geometries more accessible. In this spirit, we consider some of the geometric properties of the type IIB theory on R^6 \times M where M is an `Asymptotically Locally Euclidean (ALE)' gravitational instanton. Given the self-duality of the theory, we can extract the geometry (both singular and resolved) seen by the weakly coupled IIB string by studying the physics of a D1-brane probe. The construction is both amusing and instructive, as the physics of the probe completely captures the mathematics of the construction of ALE instantons via `HyperKahler Quotients', as presented by Kronheimer. This relation has been noted by Douglas and Moore for the A-series. We extend the explicit construction to the case of the D- and E-series -- uncovering a quite beautiful structure -- and highlight how all of the elements of the mathematical construction find their counterparts in the physics of the type IIB D-string. We discuss the explicit ALE metrics which may be obtained using these techniques, and comment on the role duality plays in relating gauged linear sigma models to conformal field theories.

hep-th↗