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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.

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.

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.

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.

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.

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.

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.

A bstract Holographic duality implies that the geometric properties of the gravitational bulk theory should be encoded in the dual field theory. These naturally include the metric on dimensions that become compact near the conformal boundary, as is the case for any asymptotically locally AdS n × $$ \mathbbm{S} $$ S k spacetime. Almost all previous work on metric reconstruction ignores these dimensions and would thus at most apply to dimensionallyreduced metrics. In this work, we generalize the approach to bulk reconstruction using lightcone cuts and propose a prescription to obtain the full higherdimensional metric of generic spacetimes up to an overall conformal factor. We first extend the definition of lightcone cuts to include information about the asymptotic compact dimensions, and show that the full conformal metric can be recovered from these extended cuts. We then give a prescription for obtaining these extended cuts from the dual field theory. The location of the usual cuts can still be obtained from bulkpoint singularities of correlators, and the new information in the extended cut can be extracted by using appropriate combinations of operators dual to KaluzaKlein modes of the higherdimensional bulk fields.

A bstract We obtain an asymptotic formula for the average value of the operator product expansion coefficients of any unitary, compact two dimensional CFT with c > 1. This formula is valid when one or more of the operators has large dimension or — in the presence of a twist gap — has large spin. Our formula is universal in the sense that it depends only on the central charge and not on any other details of the theory. This result unifies all previous asymptotic formulas for CFT2 structure constants, including those derived from crossing symmetry of four point functions, modular covariance of torus correlation functions, and higher genus modular invariance. We determine this formula at finite central charge by deriving crossing kernels for higher genus crossing equations, which give analytic control over the structure constants even in the absence of exact knowledge of the conformal blocks. The higher genus modular kernels are obtained by sewing together the elementary kernels for fourpoint crossing and modular transforms of torus onepoint functions. Our asymptotic formula is related to the DOZZ formula for the structure constants of Liouville theory, and makes precise the sense in which Liouville theory governs the universal dynamics ofmore »