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Abstract

In this thesis we study the Weak Gravity Conjecture (WGC) and the Swampland Distance Conjecture (SDC) in the context of axions. They suggest that theories containing axions with super-Planckian field ranges, such as models of large field inflation, are incompatible with quantum gravity. We challenge this statement by constructing axions with mildly super-Planckian field ranges in a compactification of type IIB string theory with fluxes. Large field distances in the corresponding 4d effective theory are only possible at the expense of an exponentially low cutoff. This is in spirit consistent with the SDC. Furthermore we study effective theories of axions with super-Planckian decay constants which hence violate the WGC. Axionic strings lead to topological inflation which may be considered a pathology of such theories. This suggests to take the naive magnetic WGC for axions seriously but we can not draw definite conclusions. Finally we investigate axionic shift symmetries which are expected to be broken by quantum gravitational effects. We point out that certain fermion operators break such symmetries and quantify the censorship of axionic shift symmetries via a conjectured lower bound on axion masses. Besides we discuss 3-forms as effective descriptions of instantons and fermion interactions generated by gravitational instantons.