The Quantum Gravity Scale and the Swampland

This thesis investigates the role of the quantum gravity cut-off for effective field theories (EFTs) coupled to Einstein gravity, with an emphasis on the Swampland program. A model-independent approach is employed so as to determine the maximum regime of validity of any such EFT, identifying the species scale as the natural candidate for the quantum gravity scale. We proceed by systematically testing this framework in string theory compactifications, yielding significant agreement with the previous perturbative and non-perturbative analysis. Additionally, we explore the most immediate implications that this picture has in the infrared regime, thus uncovering universal properties associated to the aforementioned energy scale, such as precise lower bounds on its exponential decay rates as well as certain intriguing patterns holding within the infinite distance corners of moduli space.

Supervisor: Luis E. Ibáñez Santiago.

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IFT