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Abstract

A consistent gravitational effective field theory is not guaranteed to have a UV comple- tion to Quantum Gravity. If it does, it belongs to the very restricted Landscape, while if it does not, it belongs to the Swampland. The Swampland Program aims at formulating an interconnected set of qualitative criteria, the Swampland Conjectures, which all the- ories in the Landscape should respect. The conjectures have profound implications for low-energy physics. String theory, as a theory of Quantum Gravity, is inherently related to the Swampland program. On the one hand, String Theory provides necessary evi- dence for formulating sensible conjectures. On the other hand, Swampland conjectures can uncover previously unidentified objects and consistency conditions in String Theory. The Dark Dimension proposal approaches the Cosmological Constant problem with insights from the Swampland Program combined with observational data. It makes a concrete prediction that our universe should have one extra mesoscopic dimension of a few micrometers. We propose a first string realization for the Dark Dimension proposal, using a common feature of string compactifications in the presence of higher-form fluxes, a strongly warped throat. The Cobordism Conjecture is related to the absence of global symmetries in Quantum Gravity and prohibits global cobordism charges. In practice, we start with a suitable approximation which admits such charges and then appropriately trivialize them, break- ing or gauging the global symmetry. In the case of gauging, we study the interplay of K-theory and cobordism charges and how this behaves under dimensional reduction to give charge neutrality conditions, commonly known as tadpole cancelation conditions. In the context of breaking, we work in the geometric framework of dynamical cobor- dism, which relates dynamical tadpoles to cobordism. We identify a formerly unknown, cobordism-predicted 7-brane and provide its explicit description.