Flavor Symmetry for Quarks and Leptons

Present data on neutrino masses and mixing favor the highly symmetric tribimaximal neutrino mixing matrix which suggests an underlying flavor symmetry. A systematic study of non-abelian finite groups of order $g \leq 31$ reveals that tribimaximal mixing can be derived not only from the well known tetrahedral flavor symmetry $T \equiv A_4$, but also by using the binary tetrahedral symmetry $T^{'} \equiv SL_2(F_3)$ which does not contain the tetrahedral group as a subgroup. $T^{'}$ has the further advantage that it can also neatly accommodate the quark masses including a heavy top quark.Comment: 12 pages latex. More typos correcte

Cyclic Universe and Infinite Past

We address two questions about the past for infinitely cyclic cosmology. The first is whether it can contain an infinite length null geodesic into the past in view of the Borde-Guth-Vilenkin (BGV) "no-go" theorem, The second is whether, given that a small fraction of spawned universes fail to cycle, there is an adequate probability for a successful universe after an infinite time. We give positive answers to both questions then show that in infinite cyclicity the total number of universes has been infinite for an arbitrarily long time.Comment: 7 pages. Clarification in discussion of infinite pas

Gravitation at Very Short Distances

In this note, it is discussed why attempts to renormalize conventional quantum gravity may be based on a false presumption, because, according to Verlinde's entropic view of gravity, the gravitational force between two elementary particles vanishes.Comment: 5 pages. Additional reference

The exact eigenstates of the neutrino mass matrix without CP-phase violation

In this paper we obtain the exact mass-eigenstates of the Majorana physical neutrinos. We start by taking into account a general $3\times3$ mass matrix without any CP-phase violation. It is then diagonalized by exactly solving an appropriate set of equations. The solution supplies straightforwardly the mass eigenvalues depending on the diagonal entries and mixing angles. Finally, the consequences of these analytical expressions are discussed assuming various phenomenological restrictions such as conserving the global lepton number $L=L_{e}-L_{\mu}-L_{\tau}$ and the $\mu-\tau$ interchange symmetry. The minimal absolute mass in the neutrino sector is also obtained since the two plausible scenarios invoked above are employed.Comment: 9 pages, no figure

Inverted neutrino mass hierarchies from U(1) symmetries

Motivated by effective low energy models of string origin, we discuss the neutrino masses and mixing within the context of the Minimal Supersymmetric Standard Model supplemented by a U(1) anomalous family symmetry and additional Higgs singlet fields charged under this extra U(1). In particular, we interpret the solar and atmospheric neutrino data assuming that there are only three left-handed neutrinos which acquire Majorana masses via a lepton number violating dimension-five operator. We derive the general form of the charged lepton and neutrino mass matrices when two different pairs of singlet Higgs fields develop non--zero vacuum expectation values and show how the resulting neutrino textures are related to approximate lepton flavor symmetries. We perform a numerical analysis for one particular case and obtain solutions for masses and mixing angles, consistent with experimental data.Comment: 15 pages, 4 figure

Axion and neutrino physics from anomaly cancellation

It has been recently shown that the requirement of anomaly cancellation in a (non-supersymmetric) six-dimensional version of the standard model fixes the field content to the known three generations. We discuss the phenomenological consequences of the cancellation of the local anomalies: the strong CP problem is solved and the fundamental scale of the theory is bounded by the physics of the axion. Neutrinos acquire a mass in the range suggested by atmospheric experiments.Comment: 9 pages, RevTeX

Top quark forward-backward asymmetry and charge asymmetry in left-right twin Higgs model

In order to explain the Tevatron anomaly of the top quark forward-backward asymmetry $A_{FB}^t$ in the left-right twin Higgs model, we choose to give up the lightest neutral particle of $\hat{h}$ field as a stable dark matter candidate. Then a new Yukawa interaction for $\hat{h}$ is allowed, which can be free from the constraint of same-sign top pair production and contribute sizably to $A_{FB}^t$. Considering the constraints from the production rates of the top pair ($t\bar t$), the top decay rates and $t\bar{t}$ invariant mass distribution, we find that this model with such new Yukawa interaction can explain $A_{FB}^t$ measured at the Tevatron while satisfying the charge asymmetry $A_{C}^t$ measured at the LHC.Moreover, this model predicts a strongly correlation between $A_{C}^t$ at the LHC and $A_{FB}^t$ at the Tevatron, i.e., $A_{C}^t$ increases as $A_{FB}^t$ increases.Comment: 17 pages, 9 figures; matches the published versio