Journal Article

Relaxion monodromy and the Weak Gravity Conjecture

Uranga, A. M., Valenzuela, I., Ibáñez, L. E., Montero, M.

2016

Overview

A bstract The recently proposed relaxion models require extremely large trans-Planckian axion excursions as well as a potential explicitly violating the axion shift symmetry. The latter property is however inconsistent with the axion periodicity, which corresponds to a gauged discrete shift symmetry. A way to make things consistent is to use monodromy, i.e. both the axion and the potential parameters transform under the discrete shift symmetry. The structure is better described in terms of a 3-form field C μνρ coupling to the SM Higgs through its field strength F 4 . The 4-form also couples linearly to the relaxion, in the Kaloper-Sorbo fashion. The extremely small relaxion-Higgs coupling arises in a see-saw fashion as g ≃ F 4 /f , with f being the axion decay constant. We discuss constraints on this type of constructions from membrane nucleation and the Weak Gravity Conjecture. The latter requires the existence of membranes, whose too fast nucleation could in principle drive the theory out of control, unless the cut-off scale is lowered. This allows to rule out the simplest models with the QCD axion as relaxion candidate on purely theoretical grounds. We also discuss possible avenues to embed this structure into string theory.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V
• Subject: Classical and Quantum Gravitation / Constants / Coupling / Elementary Particles / Field strength / Gravitation / Grounds / High energy physics / Membranes / Nucleation / Physics / Physics and Astronomy / Quantum Field Theories / Quantum Field Theory / Quantum Physics / Regular Article - Theoretical Physics / Relativity Theory / String Theory / Symmetry