Peccei-Quinn symmetry as the origin of Dirac Neutrino Masses

We propose a model of Dirac neutrino masses generated at one-loop level. The origin of this mass is induced from Peccei-Quinn symmetry breaking which was proposed to solve the so-called strong CP problem in QCD, therefore, the neutrino mass is connected with the QCD scale, $Lambda_{rm QCD}$. We also study the parameter space of this model confronting with neutrino oscillation data and leptonic rare decays. The phenomenological implications to leptonic flavor physics such as the electromagnetic moment of charged leptons and neutrinos are studied. Axion as the dark matter candidate is one of the byproduct in our scenario. Di-photon and Z-photon decay channels in the LHC Higgs search are investigated, we show that the effects of singly charged singlet scalar can be distinguished from the general two Higgs doublet model.

Vacuum stability, neutrinos, and dark matter

Motivated by the discovery hint of the Standard Model (SM) Higgs mass around 125 GeV at the LHC, we study the vacuum stability and perturbativity bounds on Higgs scalar of the SM extensions including neutrinos and dark matter (DM). Guided by the SM gauge symmetry and the minimal changes in the SM Higgs potential we consider two extensions of neutrino sector (Type-I and Type-III seesaw mechanisms) and DM sector (a real scalar singlet (darkon) and minimal dark matter (MDM)) respectively. The darkon contributes positively to the $beta$ function of the Higgs quartic coupling $lambda$ and can stabilize the SM vacuum up to high scale. Similar to the top quark in the SM we find the cause of instability is sensitive to the size of new Yukawa couplings between heavy neutrinos and Higgs boson, namely, the scale of seesaw mechanism. MDM and Type-III seesaw fermion triplet, two nontrivial representations of $SU(2)_{L}$ group, will bring the additional positive contributions to the gauge coupling $g_{2}$ renormalization group (RG) evolution and would also help to stabilize the electroweak vacuum up to high scale.

Binary Icosahedral Flavor Symmetry for Four Generations of Quarks and Leptons

To include the quark sector, the $A_{5}equiv I$ (icosahedron) four generation lepton model is extended to a binary icosahedral symmetry $I$ flavor model. We find the masses of fermions, including the heavy sectors, can be accommodated. At leading order the CKM matrix is the identity and the PMNS matrix, resulting from same set of vacua, corresponds to tribimaximal mixings.