https://doi.org/10.1140/epjc/s10052-018-6396-6
Regular Article - Theoretical Physics
Color unified dynamical axion
1
Department of Physics and Theoretical Physics Group, Lawrence Berkeley Laboratory, University of California, Berkeley, California, 94720, USA
2
Departamento de Física Teórica and Instituto de Física Teórica, IFT-UAM/CSIC, Universidad Autónoma de Madrid, Cantoblanco, 28049, Madrid, Spain
* e-mail: pablo.quilez@uam.es
Received:
31
May
2018
Accepted:
30
October
2018
Published online:
24
November
2018
We consider an enlarged color sector which solves the strong CP problem via new massless fermions. The spontaneous breaking of a unified color group into QCD and another confining group provides a source of naturally large axion mass 
due to small size instantons. This extra source of axion mass respects automatically the alignment of the vacuum, ensuring a low-energy CP-conserving vacuum. The mechanism does not appeal to a 
“mirror” copy of the SM, nor does it require any fine-tuning of the axion-related couplings at the unification scale. There is no very light axion and uncharacteristically the lighter spectrum contains instead sterile fermions. The axion scale 
can be naturally brought down to a few TeV, with an exotic spectrum of colored pseudoscalars lighter than this scale, observable at colliders exclusively via strong interactions. The 
parameter space which allows a solution of the strong CP problem is thus enlarged well beyond that of invisible axion models.
© The Author(s), 2018
