Abstract
We propose two models where a U(1) Peccei-Quinn global symmetry arises accidentally and is respected up to high-dimensional operators, so that the axion solution to the strong CP problem is successful even in the presence of Planck-suppressed operators. One model is SU( mathcal{N} ) gauge interactions with fermions in the fundamental and a scalar in the symmetric. The axion arises from spontaneous symmetry breaking to SO( mathcal{N} ), that confines at a lower energy scale. Axion quality in the model needs mathcal{N} ≳ 10. SO bound states and possibly monopoles provide extra Dark Matter candidates beyond the axion. In the second model the scalar is in the anti-symmetric: SU( mathcal{N} ) broken to Sp( mathcal{N} ) needs even mathcal{N} ≳ 20. The cosmological DM abundance, consisting of axions and/or super-heavy relics, can be reproduced if the PQ symmetry is broken before inflation (Boltzmann-suppressed production of super-heavy relics) or after (super-heavy relics in thermal equilibrium get partially diluted by dark glue-ball decays).
Highlights
The bound becomes stronger for higher fa and lower ΛUV
We proposed two simple models that provide a high-quality accidental PQ symmetry
The models are based on SU(N ) gauge dynamics spontaneously broken to either Sp(N ) or SO(N ) by a scalar S in the anti-symmetric or symmetric and heavy quarks and leptons in the fundamental, as summarized in table 1
Summary
We consider a gauge group GSM ⊗ SU(N ), with a new scalar S in the two-index symmetric or anti-symmetric representation of SU(N ), and new left-handed chiral Weyl fermions charged under SU(N ) as listed in table 1: one Q dubbed ‘quark’ because in the fundamental of color, and three L dubbed ‘leptons’ because uncolored. Three L are needed in order to avoid gauge anomalies and to obtain the desired PQ anomalies. The three L could be 1 ⊕ 2 or 1 ⊕ 1 ⊕ 1 under SU(2)L; as the choice does not make a big difference we assume the latter possibility and that all 3 leptons have the same hypercharge YL, for the moment left unspecified and possibly vanishing Of their hypercharges, the fermions Q and L are chiral: their mass terms are forbidden by gauge invariance for all values of the hypercharges YQ and YL. From [16], we assign non-zero SM hypercharges to the exotic fermions and show that it is possible to get rid of dangerous colored relics This enlarges the parameter space of the model to the case where the PQ is broken after inflation and opens the possibility of having extra DM candidates in the form of Sp/SO bound states. Assuming mQ ∼ mL ∼ 1011GeV, sub-Planckian Landau poles in g3 and gY are avoided if N 30 and N (YQ2 + YL2) 4
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