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A bstract Thermal partition functions for gravitational systems have traditionally been studied using Euclidean path integrals. But in Euclidean signature the gravitational action suffers from the conformal factor problem, which renders the action unbounded below. This makes it difficult to take the Euclidean formulation as fundamental. However, despite their familiar association with periodic imaginary time, thermal gravitational partition functions can also be described by realtime path integrals over contours defined by real Lorentzian metrics. The one caveat is that we should allow certain codimension2 singularities analogous to the familiar Euclidean conical singularities. With this understanding, we show that the usual Euclideansignature black holes (or their complex rotating analogues) define saddle points for the realtime path integrals that compute our partition functions. Furthermore, when the black holes have positive specific heat, we provide evidence that a codimension2 subcontour of our real Lorentzsignature contour of integration can be deformed so as to show that these black holes saddles contribute with nonzero weight to the semiclassical limit, and that the same is then true of the remaining two integrals.more » « less

A bstract In the AdS/CFT correspondence, single trace operators of large N gauge theories at large spin J can be described by classical spinning strings, giving a geometric and classical description of their spectrum at strong coupling. We observe that in AdS 3 these strings have significant gravitational backreaction at sufficiently large spin, since the gravitational force does not decay at long distances. We construct solutions for folded spinning strings coupled to gravity in AdS 3 and compute their spectrum, corresponding to the leading Regge trajectory of Virasroro primary operators. These solutions exist only below a maximal spin J < J max , and as J → J max the solution approaches an extremal rotating BTZ black hole.more » « less

null (Ed.)A bstract We describe the construction of traversable wormholes with multiple mouths in four spacetime dimensions and discuss associated quantum entanglement. Our wormholes may be traversed between any pair of mouths. In particular, in the threemouth case they have fundamental group F 2 (the free group on two generators). By contrast, connecting three regions A, B, C in pairs ( AB , BC , and AC ) using three separate wormholes would give fundamental group F 3 . Our solutions are asymptotically flat up to the presence of possible magnetic fluxes or cosmic strings that extend to infinity. The construction begins with a twomouth traversable wormhole supported by backreaction from quantum fields. Inserting a sufficiently small black hole into its throat preserves traversability between the original two mouths. This black hole is taken to be the mouth of another wormhole connecting the original throat to a new distant region of spacetime. Making the new wormhole traversable in a manner similar to the original twomouth wormhole provides the desired causal connections. From a dual field theory point of view, when AdS asymptotics are added to our construction, multiparty entanglement may play an important role in the traversability of the resulting wormhole.more » « less

null (Ed.)A bstract This work is the first step in a twopart investigation of realtime replica wormholes. Here we study the associated realtime gravitational path integral and construct the variational principle that will define its saddlepoints. We also describe the general structure of the resulting realtime replica wormhole saddles, setting the stage for construction of explicit examples. These saddles necessarily involve complex metrics, and thus are accessed by deforming the original real contour of integration. However, the construction of these saddles need not rely on analytic continuation, and our formulation can be used even in the presence of nonanalytic boundarysources. Furthermore, at least for replica and CPTsymmetric saddles we show that the metrics may be taken to be real in regions spacelike separated from a socalled ‘splitting surface’. This feature is an important hallmark of unitarity in a field theory dual.more » « less

null (Ed.)A bstract We reformulate recent insights into black hole information in a manner emphasizing operationallydefined notions of entropy, Lorentzsignature descriptions, and asymptotically flat spacetimes. With the help of replica wormholes, we find that experiments of asymptotic observers are consistent with black holes as unitary quantum systems, with density of states given by the BekensteinHawking formula. However, this comes at the cost of superselection sectors associated with the state of baby universes. Spacetimes studied by Polchinski and Strominger in 1994 provide a simple illustration of the associated concepts and techniques, and we argue them to be a natural latetime extrapolation of replica wormholes. The work aims to be selfcontained and, in particular, to be accessible to readers who have not yet mastered earlier formulations of the ideas above.more » « less

null (Ed.)A bstract We generalize the GaoJafferisWall construction of traversable twosided wormholes to multiboundary wormholes. In our construction, we take the background spacetime to be multiboundary black holes in AdS 3 . We work in the hot limit where the dual CFT state in certain regions locally resembles the thermofield double state. Furthermore, in these regions, the hot limit makes the causal shadow exponentially small. Based on these two features of the hot limit, and with the threeboundary wormhole as our main example, we show that traversability between any two asymptotic regions in a multiboundary wormhole can be triggered using a doubletrace deformation. In particular, the two boundary regions need not have the same temperature and angular momentum. We discuss the nontrivial angular dependence of traversability in our construction, as well as the effect of the causal shadow region.more » « less

null (Ed.)A bstract Multicollinear factorization limits provide a window to study how locality and unitarity of scattering amplitudes can emerge dynamically from celestial CFT, the conjectured holographic dual to gauge and gravitational theories in flat space. To this end, we first use asymptotic symmetries to commence a systematic study of conformal and KacMoody descendants in the OPE of celestial gluons. Recursive application of these OPEs then equips us with a novel holographic method of computing the multicollinear limits of gluon amplitudes. We perform this computation for some of the simplest helicity assignments of the collinear particles. The prediction from the OPE matches with Mellin transforms of the expressions in the literature to all orders in conformal descendants. In a similar vein, we conclude by studying multicollinear limits of graviton amplitudes in the leading approximation of sequential doublecollinear limits, again finding a consistency check against the leading order OPE of celestial gravitons.more » « less

null (Ed.)Charged black holes in antide Sitter space become unstable to forming charged scalar hair at low temperatures T < Tc. This phenomenon is a holographic realization of superconductivity. We look inside the horizon of these holographic superconductors and find intricate dynamical behavior. The spacetime ends at a spacelike Kasner singularity, and there is no Cauchy horizon. Before reaching the singularity, there are several intermediate regimes which we study both analytically and numerically. These include strong Josephson oscillations in the condensate and possible 'Kasner inversions' in which after many efolds of expansion, the EinsteinRosen bridge contracts towards the singularity. Due to the Josephson oscillations, the number of Kasner inversions depends very sensitively on T, and diverges at a discrete set of temperatures {Tn} that accumulate at Tc. Near these Tn, the final Kasner exponent exhibits fractallike behavior.more » « less

null (Ed.)A bstract The gravitational dual to the grand canonical ensemble of a large N holographic theory is a charged black hole. These spacetimes — for example Reissner NordströmAdS — can have Cauchy horizons that render the classical gravitational dynamics of the black hole interior incomplete. We show that a (spatially uniform) deformation of the CFT by a neutral scalar operator generically leads to a black hole with no inner horizon. There is instead a spacelike Kasner singularity in the interior. For relevant deformations, Cauchy horizons never form. For certain irrelevant deformations, Cauchy horizons can exist at one specific temperature. We show that the scalar field triggers a rapid collapse of the EinsteinRosen bridge at the wouldbe Cauchy horizon. Finally, we make some observations on the interior of charged dilatonic black holes where the Kasner exponent at the singularity exhibits an attractor mechanism in the low temperature limit.more » « less