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Open Access Publications from the University of California

Scholarly Works (8 results)

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UC Berkeley Previously Published Works (2022)
Abstract : In this paper, we propose a new gravity dual for a 2d BCFT with two conformal boundaries by introducing a defect that connects the two End-of-the-World branes. We demonstrate that the BCFT dual to this bulk model exhibits a richer lowest spectrum. The corresponding lowest energy eigenvalue can continuously interpolate between $$ -\frac{\pi c}{24\Delta x} $$ − πc 24 Δ x and 0 where ∆x is the distance between the boundaries. This range was inaccessible to the conventional AdS/BCFT model with distinct boundary conditions. We compute the holographic entanglement entropy and find that it exhibits three different phases, one of which breaks the time reflection symmetry. We also construct a wormhole saddle, analogous to a 3d replica wormhole, which connects different boundaries through the AdS bulk. This saddle is present only if the BCFT is non-unitary and is always subdominant compared to the disconnected saddle.
    Cover page: Holographic BCFT with a Defect on the End-of-the-World braneCreative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2023)

    In this dissertation, we explore these two complementary approaches to quantum gravity – holography as a bottom-up perspective and string theory as a top-down framework.

    On the holography side, we study two novel extensions of the AdS/CFT duality – TT deformed CFTs and their gravitational duals, and a two-dimensional BCFT with two conformal boundaries dual to AdS spacetime with two End-of-the-World branes that can intersect at a defect. We also develop a bulk flow procedure that can be interpreted as generating a sequence of coarse-grained holographic states. We demonstrate the existence of a novel inside-out entanglement island for the eternally inflating multiverse. We compute the entanglement entropy of free fermions in the presence of a partially transmitting boundary and use it to study entanglement islands for a blackhole with non-trivial graybody factors.

    On the string theory side, we study non-perturbative effects in minimal string theory. We compute various instanton contributions like the ZZ cylinder, the ZZ annulus one-point function, and the disk two-point function using string field theory. We also match these to results from the dual matrix model or matrix quantum mechanics.

      Cover page: Bottom-up and Top-down Approaches to a Quantum Theory of Gravity
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2020)
      Motivated by the understanding of holography as realized in tensor networks, we develop a bulk procedure that can be interpreted as generating a sequence of coarse-grained holographic states. The coarse-graining procedure involves identifying degrees of freedom entangled at short distances and disentangling them. This is manifested in the bulk by a flow equation that generates a codimension-1 object, which we refer to as the holographic slice. We generalize the earlier classical construction to include bulk quantum corrections, which naturally involves the generalized entropy as a measure of the number of relevant boundary degrees of freedom. The semiclassical coarse graining results in a flow that approaches quantum extremal surfaces such as entanglement islands that have appeared in discussions of the black hole information paradox. We also discuss the relation of the present picture to the view that the holographic dictionary works as quantum error correction.
        Cover page: Coarse-graining holographic states: A semiclassical flow in general spacetimes
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2021)
        We study the redundancies in the global spacetime description of the eternally inflating multiverse using the quantum extremal surface prescription. We argue that a sufficiently large spatial region in a bubble universe has an entanglement island surrounding it. Consequently, the semiclassical physics of the multiverse, which is all we need to make cosmological predictions, can be fully described by the fundamental degrees of freedom associated with certain finite spatial regions. The island arises due to mandatory collisions with collapsing bubbles, whose big crunch singularities indicate redundancies of the global spacetime description. The emergence of the island and the resulting reduction of independent degrees of freedom provides a regularization of infinities which caused the cosmological measure problem.
          Cover page: Multiverse in an inverted island
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2023)
          We describe two different, but equivalent semiclassical views of black hole physics in which the equivalence principle and unitarity are both accommodated. In one, unitarity is built-in, while the black hole interior emerges only effectively as a collective phenomenon involving horizon (and possibly other) degrees of freedom. In the other, more widely studied approach, the existence of the interior is manifest, while the unitarity of the underlying dynamics can be captured only indirectly by incorporating certain nonperturbative effects of gravity. These two pictures correspond to a distant description and the description based on entanglement islands/replica wormholes, respectively. We also present a holographic description of de Sitter spacetime based on the former approach, in which the holographic theory is located on the stretched horizon of a static patch. We argue that the existence of these two approaches is rooted in the two formulations of quantum mechanics: the canonical and path integral formalisms.
            Cover page: Black hole and de Sitter microstructures from a semiclassical perspectiveCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2019)
              Cover page: Comments on holographic entanglement entropy in TT deformed conformal field theories
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2022)
              Abstract : We compute the normalization of the general multi-instanton contribution to the partition function of (p′, p) minimal string theory and also to the dual two-matrix integral. We find perfect agreement between the two results.
                Cover page: Multi-instantons in minimal string theory and in matrix integralsCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2022)
                Abstract : We use insights from string field theory to analyze and cure the divergences in the cylinder diagram in minimal string theory with both boundaries lying on a ZZ brane. We focus on theories with worldsheet matter consisting of the (2, p) minimal model plus Liouville theory, with total central charge 26, together with the usual bc-ghosts. The string field theory procedure gives a finite, purely imaginary normalization constant for non-perturbative effects in minimal string theory, or doubly non-perturbative effects in JT gravity. We find precise agreement with the prediction from the dual double-scaled one-matrix integral. We also make a few remarks about the extension of this result to the more general (p′, p) minimal string.
                  Cover page: Normalization of ZZ instanton amplitudes in minimal string theoryCreative Commons 'BY' version 4.0 license
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