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Some recently proposed definitions of Jackiw-Teitelboim (JT) gravity and supergravities in terms of combinations of minimal string models are explored, with a focus on physics beyond the perturbative expansion in spacetime topology. While this formally involves solving infinite-order nonlinear differential equations, it is shown that the physics can be extracted to arbitrarily high accuracy in a simple controlled truncation scheme, using a combination of analytical and numerical methods. The nonperturbative spectral densities are explicitly computed and exhibited. The full spectral form factors, involving crucial nonperturbative contributions from wormhole geometries, are also computed and displayed, showing the nonperturbative details of the characteristic “slope,” “dip,” “ramp,” and “plateau” features. It is emphasized that results of this kind can most likely be readily extracted for other types of JT gravity using the same methods.

It is proposed that a family of Jackiw-Teitelboim supergravites, recently discussed in connection with matrix models by Stanford and Witten, can be given a complete definition, to all orders in the topological expansion and beyond, in terms of a specific combination of minimal string theories. This construction defines nonperturbative physics for the supergravity that is well defined and stable. The minimal models come from double-scaled complex matrix models and correspond to the cases (2Γ+1,2) in the Altland-Zirnbauer (α,β) classification of random matrix ensembles, where Γ is a parameter. A central role is played by a nonlinear “string equation” that naturally incorporates Γ, usually taken to be an integer, counting, e.g., D-branes in the minimal models. Here, half-integer Γ also has an interpretation. In fact, Γ=±12 yields the cases (0,2) and (2,2) that were shown by Stanford and Witten to have very special properties. These features are manifest in this definition because the relevant solutions of the string equation have special properties for Γ=±12. Additional special features for other half-integer Γ’s suggest new surprises in the supergravity models.

Recently, Saad et al. showed how to define the genus expansion of Jackiw-Teitelboim (JT) quantum gravity in terms of a double-scaled Hermitian matrix model. However, the model’s nonperturbative sector has fatal instabilities at low energy that they be cured by procedures that render the physics nonunique. This might not be a desirable property for a system that is supposed to capture key features of quantum black holes. Presented here is a model with identical zperturbative physics at high energy that instead has a stable and unambiguous nonperturbative completion of the physics at low energy. An explicit examination of the full spectral density function shows how this is achieved. The new model, which is based on complex matrix models, also allows for the straightforward inclusion of spacetime features analogous to Ramond-Ramond fluxes. Intriguingly, there is a deformation parameter that connects this nonperturbative formulation of JT gravity to one which, at low energy, has features of a super JT gravity.

Using the fact that theories of gravity with asymptotically three-dimensional anti-de Sitter geometries have dual descriptions as two-dimensional conformal field theories (CFTs), we present the first study in field theory of the thermodynamic volume of various black hole solutions. We explain in general two-dimensional CFT terms why the presence of a thermodynamic volume can render certain black hole solutions "super-entropic". Super-entropicity simply results from the fact that the Cardy formula, which gives the gravitational Bekenstein-Hawking entropy, can over-count the CFT entropy. The examples of charged Banados, Teitelbiom and Zanelli (BTZ) black holes and generalized exotic BTZ black holes are described. These observations help explain why the specific heat at constant volume can signal the instability of such solutions, as recently conjectured., 8 pages

Dualities between certain supersymmetric gauge field theories in three and four dimensions have been studied in considerable detail recently by realizing them as geometric manipulations of configurations of extended objects in type II string theory. These extended objects include {open_quotes}D-branes{close_quotes} and {open_quotes}NS-(five-)branes.{close_quotes} In constructing the brane configurations which realize dualities for orthogonal and symplectic gauge groups, an {open_quotes}orientifold{close_quotes} was introduced, which results in nonorientable string sectors. Certain features of orientifolded NS-branes{emdash}such as their existence{emdash}were assumed in the original construction, which have not been verified directly. However, those features fit very well together with the properties of the relevant field theories, and subsequently yielded the known dualities. This paper describes how orientifolded NS-branes can exist in type II string theory by displaying explicitly that the assumed combinations of world-sheet and space-time symmetries do indeed leave the NS-brane invariant and therefore can be gauged. The resulting orientifolded NS-brane can be described in terms of background fields, and furthermore as an exact conformal field theory, to exactly the same extent as the standard NS-brane. {copyright} {ital 1997} {ital The American Physical Society}

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{sup 6}{times}M, where M is an {open_quotes}asymptotically locally Euclidean{close_quotes} (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 {open_quotes}hyper-Kaehler quotients,{close_quotes} 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{emdash}uncovering a quite beautiful structure{emdash}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.

A conformal field theory representing a four-dimensional classical solution of heterotic string theory is presented. The low-energy limit of this solution has U(1) electric and magnetic charges, and also nontrivial axion and dilaton fields. The low-energy metric contains mass, NUT and rotation parameters. We demonstrate that this solution corresponds to part of an extremal limit of the Kerr-Taub-NUT dyon solution. This limit displays interesting `remnant' behaviour, in that asymptotically far away from the dyon the angular momentum vanishes, but far down the infinite throat in the neighbourhood of the horizon (described by our CFT) there is a non-zero angular velocity. A further natural generalization of the CFT to include an additional parameter is presented, but the full physical interpretation of its role in the resulting low energy solution is unclear., Comment: 43 pages, Plain TEX + epsf.tex for one uuencoded figure.

Families of exact (0,2) supersymmetric conformal field theories of magnetically and electrically charged extremal 4D black hole solutions of heterotic string theory are presented. They are constructed using a (0,1) supersymmetric SL(2,[ital openR])[times]SU(2) Weiss-Zumino-Witten model where anomalously embedded U(1)[times]U(1) subgroups are gauged. Crucial cancellations of the U(1) anomalies coming from the supersymmetric fermions, the current algebra fermions, and the gauging ensure that there is a consistency of these models at the quantum level. Various 2D models, which may be considered as building blocks for extremal 4D constructions, are presented. They generalize the class of 2D models which might be obtained from gauging SL(2,[ital openR]) and coincide with known heterotic string backgrounds. The exact conformal field theory presented by Giddings, Polchinski, and Strominger describing the angular sector of the extremal magnetically charged black hole is a special case of this construction. An example where the radial and angular theories are mixed nontrivially is studied in detail, resulting in an extremal dilatonic Taub-NUT-like dyon.

We give a detailed account of the construction of non--trivial localized solutions in a 2+1 dimensional model of superconductors using a 3+1 dimensional gravitational dual theory of a black hole coupled to a scalar field. The solutions are found in the presence of a background magnetic field. We use numerical and analytic techniques to solve the full Maxwell--scalar equations of motion in the background geometry, finding condensate droplet solutions, and vortex solutions possessing a conserved winding number. These solutions and their properties, which we uncover, help shed light on key features of the (B,T) phase diagram., 31 pages, 10 figures. Included the discussion from arXiv:0906.0519 to make the paper self-contained

In studying the dynamics of large N{sub c}, SU(N{sub c}) gauge theory at finite temperature with fundamental quark flavors in the quenched approximation, we observe a first order phase transition. A quark condensate forms at finite quark mass, and the value of the condensate varies smoothly with the quark mass for generic regions in parameter space. At a particular value of the quark mass, there is a finite discontinuity in the condensate's vacuum expectation value, corresponding to a first order phase transition. We study the gauge theory via its string dual formulation using the AdS/CFT conjecture, the string dual being the near-horizon geometry of N{sub c} D3-branes at finite temperature, AdS{sub 5}-SchwarzschildxS{sup 5}, probed by a D7-brane. The D7-brane has topology R{sup 4}xS{sup 3}xS{sup 1} and allowed solutions correspond to either the S{sup 3} or the S{sup 1} shrinking away in the interior of the geometry. The phase transition represents a jump between branches of solutions having these two distinct D-brane topologies. The transition also appears in the meson spectrum.

We study an exact model of string theory propagating in a space-time containing regions with closed time-like curves (CTCs) separated from a finite cosmological region bounded by a Big Bang and a Big Crunch. The model is an non-trivial embedding of the Taub-NUT geometry into heterotic string theory with a full conformal field theory (CFT) definition, discovered over a decade ago as a heterotic coset model. Having a CFT definition makes this an excellent laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and the Milne/Misner-type chronology horizon which separates them. In an effort to uncover the role of stringy corrections to such geometries, we calculate the complete set of alpha' corrections to the geometry. We observe that the key features of Taub-NUT persist in the exact theory, together with the emergence of a region of space with Euclidean signature bounded by time-like curvature singularities. Although such remarks are premature, their persistence in the exact geometry is suggestive that string theory theory is able to make physical sense of the Milne/Misner singularities and the CTCs, despite their pathological character in General Relativity. This may also support the possibility that CTCs may be viable in some physical situations, and may be a natural ingredient in pre-Big-Bang cosmological scenarios., 37 pages, 4 figures. V2: discussion of computation of metric refined, references added

We reconsider supersymmetric five dimensional rotating charged black holes, and their description in terms of D-branes. By wrapping some of the branes on K3, we are able to explore the role of the enhancon mechanism in this system. We verify that enhancon loci protect the black hole from violations of the Second Law of Thermodynamics which would have been achieved by the addition of certain D-brane charges. The same charges can potentially result in the formation of closed time-like curves by adding them to holes initially free of them, and so the enhancon mechanism forbids this as well. Although this latter observation is encouraging, it is noted that this mechanism alone does not eliminate closed time-like curves from these systems, but is in accord with earlier suggestions that they may not be manufactured, in this context, by physical processes., Comment: 18 pages, LaTeX

The enhancon mechanism removes a family of time-like singularities from certain supergravity spacetimes by forming a shell of branes on which the exterior geometry terminates. The problematic interior geometry is replaced by a new spacetime, which in the prototype extremal case is simply flat. We show that this excision process, made inevitable by stringy phenomena such as enhanced gauge symmetry and the vanishing of certain D-branes' tension at the shell, is also consistent at the purely gravitational level. The source introduced at the excision surface between the interior and exterior geometries behaves exactly as a shell of wrapped D6-branes, and in particular, the tension vanishes at precisely the enhancon radius. These observations can be generalised, and we present the case for non-extremal generalisations of the geometry, showing that the procedure allows for the possibility that the interior geometry contains an horizon. Further knowledge of the dynamics of the enhancon shell itself is needed to determine the precise position of the horizon, and to uncover a complete physical interpretation of the solutions., Comment: 31 pages, 3 figures, latex, psfig (v2: a few typo's corrected. In conclusions section, added enhancements to discussion of available choices of interior for non-extremal enhancons.)

Supergravity solutions related to large N SU(N) pure gauge theories with eight supercharges have recently been shown to give rise to an ``enhancon'', a new type of hypersurface made of D-branes. We show that enhancons also arise in similar situations pertaining to SO(2N+1), USp(2N) and SO(2N) gauge theories, using orientifolds. Enhancons therefore appear to come in types A, B, C, and D. The latter three differ globally from type A by having an extra Z_2 identification, and are distinguished locally by their subleading behaviour in large N. We focus mainly on 2+1 dimensional gauge theory, where a relation to M-theory and the Atiyah-Hitchin and Taub-NUT manifolds enables the construction of the smooth supergravity solution and the study of some of the 1/N corrections. The role of the enhancon in eleven dimensional supergravity is also uncovered. There is a close relation to certain multi-monopole moduli space problems., 26 pages, 2 figures (v2: references added)