Effects of quark family nonuniversality in SU(3)_c X SU(4)_L X U(1)_x models

Flavour changing neutral currents arise in the $SU(3)_c\otimes SU(4)_L\otimes U(1)_X$ extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the Z-pole, atomic parity violation data and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales $M_{Z_2}$ and $M_{Z_3}$ of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on $M_{Z_2}$ and $M_{Z_3}$ as low as possible without violating experimental constraints.Comment: 27 pages, 10 tables, 2 figures. Equation (19) and typos corrected. Matches version to appear in Phys. Rev.

Chiral Compactification on a Square

We study quantum field theory in six dimensions with two of them compactified on a square. A simple boundary condition is the identification of two pairs of adjacent sides of the square such that the values of a field at two identified points differ by an arbitrary phase. This allows a chiral fermion content for the four-dimensional theory obtained after integrating over the square. We find that nontrivial solutions for the field equations exist only when the phase is a multiple of \pi/2, so that this compactification turns out to be equivalent to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are either periodic or anti-periodic. The equality of the Lagrangian densities at the identified points in conjunction with six-dimensional Lorentz invariance leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in section 2. Minor corrections made in section

Flavor Structure in F-theory Compactifications

F-theory is one of frameworks in string theory where supersymmetric grand unification is accommodated, and all the Yukawa couplings and Majorana masses of right-handed neutrinos are generated. Yukawa couplings of charged fermions are generated at codimension-3 singularities, and a contribution from a given singularity point is known to be approximately rank 1. Thus, the approximate rank of Yukawa matrices in low-energy effective theory of generic F-theory compactifications are minimum of either the number of generations N_gen = 3 or the number of singularity points of certain types. If there is a geometry with only one E_6 type point and one D_6 type point over the entire 7-brane for SU(5) gauge fields, F-theory compactified on such a geometry would reproduce approximately rank-1 Yukawa matrices in the real world. We found, however, that there is no such geometry. Thus, it is a problem how to generate hierarchical Yukawa eigenvalues in F-theory compactifications. A solution in the literature so far is to take an appropriate factorization limit. In this article, we propose an alternative solution to the hierarchical structure problem (which requires to tune some parameters) by studying how zero mode wavefunctions depend on complex structure moduli. In this solution, the N_gen x N_gen CKM matrix is predicted to have only N_gen entries of order unity without an extra tuning of parameters, and the lepton flavor anarchy is predicted for the lepton mixing matrix. We also obtained a precise description of zero mode wavefunctions near the E_6 type singularity points, where the up-type Yukawa couplings are generated.Comment: 148 page

Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region

International audienceThe field-aligned neutral oscillations in the F-region (altitudes between 165 and 275 km) were compared using data obtained simultaneously with two independent instruments: the European Incoherent Scatter (EISCAT) UHF radar and a scanning Fabry-Perot interferometer (FPI). During the night of February 8, 1997, simultaneous observations with these instruments were conducted at Tromsø, Norway. Theoretically, the field-aligned neutral wind velocity can be obtained from the field-aligned ion velocity and by diffusion and ambipolar diffusion velocities. We thus derived field-aligned neutral wind velocities from the plasma velocities in EISCAT radar data. They were compared with those observed with the FPI (?=630.0 nm), which are assumed to be weighted height averages of the actual neutral wind. The weighting function is the normalized height dependent emission rate. We used two model weighting functions to derive the neutral wind from EISCAT data. One was that the neutral wind velocity observed with the FPI is velocity integrated over the entire emission layer and multiplied by the theoretical normalized emission rate. The other was that the neutral wind velocity observed with the FPI corresponds to the velocity only around an altitude where the emission rate has a peak. Differences between the two methods were identified, but not completely clarified. However, the neutral wind velocities from both instruments had peak-to-peak correspondences at oscillation periods of about 10–40 min, shorter than that for the momentum transfer from ions to neutrals, but longer than from neutrals to ions. The synchronizing motions in the neutral wind velocities suggest that the momentum transfer from neutrals to ions was thought to be dominant for the observed field-aligned oscillations rather than the transfer from ions to neutrals. It is concluded that during the observation, the plasma oscillations observed with the EISCAT radar at different altitudes in the F-region are thought to be due to the motion of neutrals.Key words: Ionosphere (Ionosphere–atmosphere interactions) – Meteorology and atmospheric dynamics (thermospheric dynamics; waves and tides)</p

Gauge-Fermion Unification and Flavour Symmetry

After we study the 6-dimensional ${\cal N} = (1, 1)$ supersymmetry breaking and $R$ symmetry breaking on $M^4\times T^2/Z_n$, we construct two ${\cal N} = (1, 1)$ supersymmetric $E_6$ models on $M^4\times T^2/Z_3$ where $E_6$ is broken down to $SO(10)\times U(1)_X$ by orbifold projection. In Model I, three families of the Standard Model fermions arise from the zero modes of bulk vector multiplet, and the $R$ symmetry $U(1)_F^{I} \times SU(2)_{{\bf 4}_-}$ can be considered as flavour symmetry. This may explain why there are three families of fermions in the nature. In Model II, the first two families come from the zero modes of bulk vector multiplet, and the flavour symmetry is similar. In these models, the anomalies can be cancelled, and we have very good fits to the SM fermion masses and mixings. We also comment on the ${\cal N}=(1, 1)$ supersymmetric $E_6$ models on $M^4\times T^2/Z_4$ and $M^4\times T^2/Z_6$, SU(9) models on $M^4\times T^2/Z_3$, and SU(8) models on $T^2$ orbifolds.Comment: Latex, 33 pages, minor change

Inflationary Cosmology with Five Dimensional SO(10)

We discuss inflationary cosmology in a five dimensional SO(10) model compactified on $S^1/(Z_2\times Z_2')$, which yields $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_X$ below the compactification scale. The gauge symmetry $SU(5)\times U(1)_X$ is preserved on one of the fixed points, while ``flipped'' $SU(5)'\times U(1)'_X$ is on the other fixed point. Inflation is associated with $U(1)_X$ breaking, and is implemented through $F$-term scalar potentials on the two fixed points. A brane-localized Einstein-Hilbert term allows both branes to have positive tensions during inflation. The scale of $U(1)_X$ breaking is fixed from $\delta T/T$ measurements to be around $10^{16}$ GeV, and the scalar spectral index $n=0.98-0.99$. The inflaton field decays into right-handed neutrinos whose subsequent out of equilibrium decay yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in PR

Semi-simple group unification in the supersymmetric brane world

The conventional supersymmetric grand unified theories suffer from two serious problems, the large mass splitting between doublet and triplet Higgs multiplets, and the too long lifetime of the proton. A unification model based on a semi-simple group SU(5)_{GUT} \times U(3)_H has been proposed to solve both of the problems simultaneously. Although the proposed model is perfectly consistent with observations, there are various mysteries. In this paper, we show that such mysterious features in the original model are naturally explained by embedding the model into the brane world in a higher dimensional space-time. In particular, the relatively small gauge coupling constant of the SU(5)_{GUT} at the unification energy scale is a consequence of relatively large volume of extra dimensions. Here, we put the SU(5)_{GUT} gauge multiplet in a 6-dimensional bulk and assume all fields in the U(3)_H sector to reside on a 3-dimensional brane located in the bulk. On the other hand, all chiral multiplets of quarks, leptons and Higgs are assumed to reside on a 3-brane at a T^2/Z_4 orbifold fixed point. The quasi-N=2 supersymmetry in the hypercolor U(3)_H sector is understood as a low-energy remnant of the N=4 supersymmetry in a 6-dimensional space-time. We further extend the 6-dimensional model to a 10-dimensional theory. Possible frameworks of string theories are also investigated to accommodate the present brane-world model. We find that the type IIB string theory with D3-D7 brane structure is an interesting candidate.Comment: 45 pages, including 1 figure, minor correctio

Strongly Coupled Grand Unification in Higher Dimensions

We consider the scenario where all the couplings in the theory are strong at the cut-off scale, in the context of higher dimensional grand unified field theories where the unified gauge symmetry is broken by an orbifold compactification. In this scenario, the non-calculable correction to gauge unification from unknown ultraviolet physics is naturally suppressed by the large volume of the extra dimension, and the threshold correction is dominated by a calculable contribution from Kaluza-Klein towers that gives the values for \sin^2\theta_w and \alpha_s in good agreement with low-energy data. The threshold correction is reliably estimated despite the fact that the theory is strongly coupled at the cut-off scale. A realistic 5d supersymmetric SU(5) model is presented as an example, where rapid d=6 proton decay is avoided by putting the first generation matter in the 5d bulk.Comment: 17 pages, latex, to appear in Phys. Rev.