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Abstract

The swampland program aims at answering the question of whether and how effective quantum field theories coupled to gravity can be UV-completed. Our limited understanding of the issues that can arise in this process is reflected in a steadily growing zoo of swampland conjectures. These are supposed to be necessary criteria for such a UV-completion and are motivated from our understanding of black hole thermodynamics, holography and string theory. The swampland conjectures can potentially have dramatic implications for physical models of real-world phenomena if they are proven in string theory. For example, they could rule out large field inflation, a cosmological constant, or non-vanishing masses of the standard model photon and graviton. The purpose of this work is to contribute to a better understanding of these conjectures by testing them in various corners of string theory. Furthermore, we reveal a complicated network of relations between the swampland conjectures. This hints at the existence of a deeper underlying structure, which is yet to be fully uncovered. One of the suggested swampland conjectures is the distance conjecture. It states that effective field theories have a finite range of validity in scalar field space, after which they necessarily break down due to an infinite tower of states becoming light. We quantify this range and identify the tower of states in the context of moduli spaces of Calabi-Yau compactifications with N = 2 supersymmetry. We claim that an analogous tower of states appears also in the limit where we send the mass of a spin-2 field to zero. We concretize this expectation in form of a spin-2 swampland conjecture. Finally, we investigate the question of whether the KKLT construction of de Sitter vacua in string theory is consistent. In this way, we challenge a recently proposed de Sitter swampland conjecture, which claims that de Sitter space cannot be a vacuum of string theory.