Shao‐Long Chen

We discuss the possibility of flavor symmetries to explain the pattern of charged lepton and neutrino masses and mixing angles. We emphasize what are the obstacles for the generation of an almost maximal atmospheric mixing and what are the minimal ingredients to obtain it. A model based on the discrete symmetry ${S}_{3}$ is constructed, which leads to the dominant $\ensuremath{\mu}\ensuremath{\tau}$-block in the neutrino mass matrix, thus predicting normal hierarchy. This symmetry makes it possible to reproduce current data and predicts $0.01\ensuremath{\lesssim}{\ensuremath{\theta}}_{13}\ensuremath{\lesssim}0.03$ and strongly suppressed neutrinoless $2\ensuremath{\beta}$-decay. Moreover, it implies a relation between lepton and quark mixing angles: ${\ensuremath{\theta}}_{23}^{q}\ensuremath{\approx}2(\ensuremath{\pi}/4\ensuremath{-}{\ensuremath{\theta}}_{23})$. The Cabibbo mixing can also be reproduced and ${\ensuremath{\theta}}_{13}^{q}\ensuremath{\sim}{\ensuremath{\theta}}_{12}^{q}{\ensuremath{\theta}}_{23}^{q}$. ${S}_{3}$ is thus a candidate to describe all the basic features of standard model fermion masses and mixing.

We study interactions of unparticles $\mathcal{U}$ of dimension ${d}_{\mathcal{U}}$ due to Georgi with standard model (SM) fields through effective operators. The unparticles describe the low energy physics of a nontrivial scale invariant sector. Since unparticles come from beyond the SM physics, it is plausible that they transform as a singlet under the SM gauge group. This helps tremendously in limiting possible interactions. We analyze interactions of scalar $\mathcal{U}$, vector ${\mathcal{U}}^{\ensuremath{\mu}}$, and spinor ${\mathcal{U}}^{s}$ unparticles with SM fields and derivatives up to dimension four. Using these operators, we discuss different features of producing unparticles at an ${e}^{+}{e}^{\ensuremath{-}}$ collider and other phenomenologies. It is possible to distinguish different unparticles produced at an ${e}^{+}{e}^{\ensuremath{-}}$ collider by looking at various distributions of production cross sections.

In a recent paper, four of the present authors proposed a class of dark matter models where generalized parity symmetry leads to equality of dark matter abundance with baryon asymmetry of the Universe and predicts dark matter mass to be around 5 GeV. In this paper, we explore how this model can be tested in direct search experiments. In particular, we point out that if the dark matter happens to be the mirror neutron, the direct detection cross section has the unique feature that it increases at low recoil energy unlike the case of conventional weakly interacting massive particles. It is also interesting to note that the predicted spin-dependent scattering could make significant contribution to the total direct detection rate, especially for light nucleus. With this scenario, one could explain recent DAMA and CoGeNT results.