Abstract
We consider a 5D extension of the DFSZ axion model that addresses both the axion quality and fermion mass hierarchy problems, and predicts flavour-dependent, off-diagonal axion-fermion couplings. The axion is part of a 5D complex scalar field charged under a U(1)PQ symmetry that is spontaneously broken in the bulk, and is insensitive to explicit PQ breaking on the UV boundary. Bulk Standard Model fermions interact with two Higgs doublets that can be localized on the UV boundary or propagate in the bulk to explain the fermion masses and mixings. When the Higgs doublets are localized on the UV boundary, they induce flavour diagonal couplings between the fermions and the axion. However, when the Higgs doublets propagate in the bulk, the overlap of the axion and fermion profiles generates flavour off-diagonal couplings. The effective scale of these off-diagonal couplings in both the quark and lepton sectors can be as small as 1011 GeV, and therefore will be probed in future precision flavour experiments.
Highlights
A popular solution of the strong CP problem involves extending the Standard Model by introducing a new particle, the axion
The axion is part of a 5D complex scalar field charged under a U(1)PQ symmetry that is spontaneously broken in the bulk, and is insensitive to explicit PQ breaking on the UV boundary
In this paper we have extended the original DFSZ model to a slice of AdS5, where the axion and Standard Model fermions propagate in the bulk containing a U(1)PQ symmetry
Summary
A popular solution of the strong CP problem involves extending the Standard Model by introducing a new particle, the axion This pseudoscalar boson arises from the PecceiQuinn (PQ) mechanism [1], where an anomalous U(1)PQ global symmetry is spontaneously broken [2, 3]. For a boundary-localized Higgs sector, only flavour-diagonal couplings are generated This follows from the orthonormality of the bulk fermion profiles. A 5D Chern-Simons term can generate an axion coupling to gauge bosons, and we show how such interactions arise from integrating out bulk fermions, extending the calculation of ref. The boundary axion couplings can be related to a 5D Chern Simons interaction and this connection is presented in appendix C
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
