No abstract

We present a model based on the SU (3) C ⊗ SU (3) L ⊗ U (1) X gauge symmetry that relates the mass hierarchy of the fermions with the solution to the strong CP problem through the U (1) P Q Peccei-Quinn symmetry. This last symmetry arises accidentally with the imposition of a discrete Z 9 symmetry, which also secludes the different scales in the double seesaw mechanism taking place in the neutrino sector. The symmetry breakdown is performed by three scalar triplets plus a scalar singlet hosting an axion field, whose particle excitation can be a component of dark matter. We show a mechanism where a small effective vev is generated for a scalar triplet which is supposed to have a bare mass above the energy scale where the SU (3) L ⊗ U (1) X symmetry is broken. Combined with the energy scale in which the U (1) P Q is broken, such a mechanism gives rise to a natural hierarchy to the fermions. Beyond the Standard Model particle content, the model predicts an invisible axion, a, three GeV neutrinos, N iL , plus several new particles at the TeV scale which are: five vector bosons, U ± , V 0 , V 0 † , and Z ; one up-type U , and two down-type D a quarks; and at least a CP-even, H 1 , plus non-hermitian neutral, φ 0 , φ 0 † , scalar bosons. The model may be tested by looking for the possible production of such particles at the LHC.

In this work, prospects to probe an overlooked facet of axion-like particles (ALPs)-their potential couplings to sterile neutrinos-are presented. We found that mono-photon searches have the potential to constrain ALP couplings to sterile neutrinos when a new heavy scalar boosts the ALP decay yields. Working within an effective field theory (EFT) approach, we scan the parameters space to establish the reach of the 13 TeV LHC to probe such couplings. We found regions of the parameters space evading several experimental constraints that can be probed at the LHC. Moreover, a complementary role between the LHC and various experiments that search for axions and ALPs can be anticipated for models where ALPs interact with sterile neutrinos. We also present the UV realization of a model having an axion-like particle, a heavy scalar and sterile neutrinos whose parameters are spanned by our EFT approach. The proposed model contains a type of seesaw mechanism for generating masses for the active neutrinos along with sterile neutrinos involving the high energy scale of the spontaneous breaking of the global symmetry associated to the ALP. Some benchmark points of this model can be discovered at the 13 TeV LHC with 300 fb −1 .