The String Landscape, the Swampland, and the Missing Corner PoS(TASI2017)015 T. Daniel Brennana, Federico Cartab,∗ and Cumrun Vafayc a Department of Physics and Astronomy, Rutgers University 126 Frelinghuysen Rd., Piscataway NJ 08855, USA b Instituto de Física Teórica UAM-CSIC, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain c Jefferson Physical Laboratory, Harvard University Cambridge, MA 02138, USA Email:
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[email protected] We give a brief overview of the string landscape and techniques used to construct string com- pactifications. We then explain how this motivates the notion of the swampland and review a number of conjectures that attempt to characterize theories in the swampland. We also compare holography in the context of superstrings with the similar, but much simpler case of topological string theory. For topological strings, there is a direct definition of topological gravity based on a sum over a “quantum gravitational foam.” In this context, holography is the statement of an identification between a gravity and gauge theory, both of which are defined independently of one another. This points to a missing corner in string dualities which suggests the search for a direct definition of quantum theory of gravity rather than relying on its strongly coupled holographic dual as an adequate substitute (Based on TASI 2017 lectures given by C. Vafa). Theoretical Advanced Study Institute in Elementary Partical Physics (TASI): “Physics at the Fundamental Frontier” University of Colorado, Boulder Boulder, CO June, 5 – 30 2017 ∗La Caixa-Severo Ochoa Scholar ySpeaker. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).