Quark Mixings in SU(6)×SU(2)RSU(6)\times SU(2)_R and Suppression of VubV_{ub}

The quark mixing matrix $V_{CKM}$ is studied in depth on the basis of superstring inspired $SU(6)\times SU(2)_R$ model with global flavor symmetries. The sizable mixings between right-handed down-type quark $D^c$ and colored Higgs field $g^c$ potentially occur but no such mixings in up-type quark sector. In the model the hierarchical pattern of $V_{CKM}$ is understood systematically. It is shown that due to large $D^c$-$g^c$ mixings $V_{ub}$ is naturally suppressed compared to $V_{td}$. It is pointed out that the observed suppression of $V_{ub}$ is in favor of the presence of $SU(2)_R$ gauge symmetry but not in accord with generic SU(5) GUT.Comment: 10pages with no figure, Latex fil

Quantization of the scalar field in a static quantum metric

We investigate the Hamiltonian formulation of quantum scalar fields in a static quantum metric. We derive a functional integral formula for the propagator. We show that the quantum metric substantially changes the behaviour of the scalar propagator and the effective Yukawa potential.Comment: Latex, 12 page

The \Phi^4 quantum field in a scale invariant random metric

We discuss a D-dimensional Euclidean scalar field interacting with a scale invariant quantized metric. We assume that the metric depends on d-dimensional coordinates where d<D. We show that the interacting quantum fields have more regular short distance behaviour than the free fields. A model of a Gaussian metric is discussed in detail. In particular, in the \Phi^4 theory in four dimensions we obtain explicit lower and upper bounds for each term of the perturbation series. It turns out that there is no coupling constant renormalization in the \Phi^4 model in four dimensions. We show that in a particular range of the scale dimension there are models in D=4 without any divergencies

Energy-Scale Dependence of the Lepton-Flavor-Mixing Matrix

We study an energy-scale dependence of the lepton-flavor-mixing matrix in the minimal supersymmetric standard model with the effective dimension-five operators which give the masses of neutrinos. We analyze the renormalization group equations of kappa_{ij}s which are coefficients of these effective operators under the approximation to neglect the corrections of O(\kappa^2). As a consequence, we find that all phases in $\kappa$ do not depend on the energy-scale, and that only n_g-1 (n_g: generation number) real independent parameters in the lepton-flavor-mixing matrix depend on the energy-scale.Comment: 6 pages, no figur

The effect of Majorana phase in degenerate neutrinos

There are physical Majorana phases in the lepton flavor mixing matrix when neutrinos are Majorana fermions. In the case of two degenerate neutrinos, the physical Majorana phase plays the crucial role for the stability of the maximal flavor mixing between the second and the third generations against quantum corrections. The physical Majorana phase of $\pi$ guarantees the maximal mixing to be stable against quantum corrections, while the Majorana phase of zero lets the maximal mixing be spoiled by quantum corrections when neutrino masses are of O(eV). The continuous change of the Majorana phase from $\pi$ to 0 makes the maximal mixing be spoiled by quantum corrections with O(eV) degenerate neutrino masses. On the other hand, when there is the large mass hierarchy between neutrinos, the maximal flavor mixing is not spoiled by quantum corrections independently of the Majorana phase.Comment: 7 pages, 1 figures, LaTe

Phenomenology of Neutrino Mass Matrix

The search for possible mixing patterns of charged leptons and neutrinos is important to get clues of the origin of nearly maximal mixings, since there are some preferred bases of the lepton mass matrices given by underlying theories. We systematically examine the mixing patterns which could lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data if taking into account phase factors in the mixing matrices. Only 6 patterns of them can explain the observed data without any tuning of parameters, while the others need particular choices for phase values.Comment: revised reference

5D seesaw, flavor structure, and mass textures

In the 5D theory in which only 3 generation right-handed neutrinos are in the bulk, the neutrino flavor mixings and the mass spectrum can be constructed through the seesaw mechanism. The 5D seesaw is easily calculated just by a replacement of the Majorana mass eigenvalues, M_i, by 2 M_*tan(h)[\pi RM_i] (M_*: 5D Planck scale, R: compactification radius). The 5D features appear when the bulk mass, which induces the 4D Majorana mass, is the same as the compactification scale or larger than it. Depending on the type of bulk mass, the seesaw scales of the 3 generations are strongly split (the tan-function case) or degenerate (the tanh-function case). In the split case, the seesaw enhancement is naturally realized. The single right-handed neutrino dominance works in a simple setup, and some specific mass textures, which are just assumptions in the 4D setup, can be naturally obtained in 5 dimensions. The degenerate case is also useful for a suitable neutrino flavor structure.Comment: 15 page

Fermion Masses and Mixings in a String Inspired Model

In the context of Calabi-Yau string models we explore the origin of characteristic pattern of quark-lepton masses and the CKM matrix. The discrete $R$-symmetry $Z_K \times Z_2$ is introduced and the $Z_2$ is assigned to the $R$-parity. The gauge symmetry at the string scale, $SU(6) \times SU(2)_R$, is broken into the standard model gauge group at a very large intermediate energy scale. At energies below the intermediate scale down-type quarks and also leptons are mixed with unobserved heavy states, respectively. On the other hand, there are no such mixings for up-type quarks. Due to the large mixings between light states and heavy ones we can derive phenomenologically viable fermion mass hierarchies and the CKM matrix. Mass spectra for intermediate-scale matter beyond the MSSM are also determined. Within this framework proton lifetime is long enough to be consistent with experimental data. As for the string scale unification of gauge couplings, however, consistent solutions are not yet found.Comment: 49 pages, 1 figure, Latex Revised version includes discussion on FCNC problems. Final version to appear in Prog. Theor. Phys. Vol.96 No.

Thermal leptogenesis in a supersymmetric neutrinophilic Higgs model

We investigate thermal leptogenesis in a supersymmetric neutrinophilic Higgs model by taking phenomenological constraints into account, where, in addition to the minimal supersymmetric standard model, we introduce an extra Higgs field with a tiny vacuum expectation value (VEV) which generates neutrino masses. Thanks to this tiny VEV of the neutrinophilic Higgs, our model allows to reduce the mass of the lightest right-handed (s)neutrino to be ${\cal O}(10^5)$ GeV as keeping sufficiently large CP asymmetry in its decay. Therefore, the reheating temperature after inflation is not necessarily high, hence this scenario is free from gravitino problem.Comment: 5 pages, 1 figur