Planckian axions and the Weak Gravity Conjecture

Thomas C. Bachlechner, Cody Long, Liam McAllister
2016 Journal of High Energy Physics  
Several recent works have claimed that the Weak Gravity Conjecture (WGC) excludes super-Planckian displacements of axion fields, and hence large-field axion inflation, in the absence of monodromy. We argue that in theories with N≫1 axions, super-Planckian axion diameters D are readily allowed by the WGC. We clarify the nontrivial relationship between the kinetic matrix K --- unambiguously defined by its form in a Minkowski-reduced basis --- and the diameter of the axion fundamental domain,
more » ... mental domain, emphasizing that in general the diameter is not solely determined by the eigenvalues f_1^2 < ... < f_N^2 of K: the orientations of the eigenvectors with respect to the identifications imposed by instantons must be incorporated. In particular, even if one were to impose the condition f_N S M_pl/f_N, with S a fixed constant, but in the universal limit S≳ S√(N)M_pl/f_N. Thus, having f_N>M_pl does not immediately imply the existence of unsuppressed higher harmonic contributions to the potential. Finally, we argue that in effective axion-gravity theories, the zero-form version of the WGC can be satisfied by gravitational instantons that make negligible contributions to the potential.
doi:10.1007/jhep01(2016)091 fatcat:gsf5drwbczexdifjvozioellsu