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

How Can We Obtain a Large Majorana-Mass in Calabi-Yau Models ?

In a certain type of Calabi-Yau superstring models it is clarified that the symmetry breaking occurs by stages at two large intermediate energy scales and that two large intermediate scales induce large Majorana-masses of right-handed neutrinos. Peculiar structure of the effective nonrenormalizable interactions is crucial in the models. In this scheme Majorana-masses possibly amount to O(10^{9 \sim 10}\gev) and see-saw mechanism is at work for neutrinos. Based on this scheme we propose a viable model which explains the smallness of masses for three kind of neutrinos $\nu _e, \nu _{\mu} \ {\rm and}\ \nu _{\tau}$. Special forms of the nonrenormalizable interactions can be understood as a consequence of an appropriate discrete symmetry of the compactified manifold.Comment: 30-pages + 6-figures, LaTeX, Preprint DPNU-94-02, AUE-01-9

Supersymmetry breaking as the origin of flavor

We present an effective flavor model for the radiative generation of fermion masses and mixings based on a SU(5)xU(2) symmetry. We assume that the original source of flavor breaking resides in the supersymmetry breaking sector. Flavor violation is transmitted radiatively to the fermion Yukawa couplings at low energy through finite supersymmetric threshold corrections. This model can fit the fermion mass ratios and CKM matrix elements, explain the non-observation of proton decay, and overcome present constraints on flavor changing processes through an approximate radiative alignment between the Yukawa and the soft trilinear sector. The model predicts new relations between dimensionless fermion mass ratios in the three fermion sectors, and the quark mixing angles.Comment: 14 pages, RevTex

Secondary Crack Formation as Fracture Mechanism in Nanocomposites of Epoxy and Fullerene-Like WS2

Fullerene-like WS2 (IF-WS2) nanoparticles (NPs) were used as a toughening agent in epoxy nanocomposites. Already 0.5 % IF-WS2 by mass increased the critical energy release rate GIc by 45 % to 62 %. Conicsection-shaped crack lines were observed on the fracture surfaces in some distance to the NPs. Nanomechanical AFM modulus measurements showed, however, no measurable differences between the modulus distribution in the vicinity of the NPs and the bulk epoxy. Possible secondary crack formation at the NPs explains the crack lines nicely. The crack line geometry allows determining the relative velocity of the secondary crack. Topographic AFM showed vertical steps several hundred nanometers high at the crack lines, indicating shear fracture and suggesting the presence of numerous subsurface cracks, which might explain the toughness increase

Minimal gauge-Higgs unification with a flavour symmetry

We show that a flavour symmetry a la Froggatt-Nielsen can be naturally incorporated in models with gauge-Higgs unification, by exploiting the heavy fermions that are anyhow needed to realize realistic Yukawa couplings. The case of the minimal five-dimensional model, in which the SU(2)_L x U(1)_Y electroweak group is enlarged to an SU(3)_W group, and then broken to U(1)_em by the combination of an orbifold projection and a Scherk-Schwarz twist, is studied in detail. We show that the minimal way of incorporating a U(1)_F flavour symmetry is to enlarge it to an SU(2)_F group, which is then completely broken by the same orbifold projection and Scherk-Schwarz twist. The general features of this construction, where ordinary fermions live on the branes defined by the orbifold fixed-points and messenger fermions live in the bulk, are compared to those of ordinary four-dimensional flavour models, and some explicit examples are constructed.Comment: LaTex, 37 pages, 2 figures; some clarifying comments and a few references adde

Green functions and dimensional reduction of quantum fields on product manifolds

We discuss Euclidean Green functions on product manifolds P=NxM. We show that if M is compact then the Euclidean field on P can be approximated by its zero mode which is a Euclidean field on N. We estimate the remainder of this approximation. We show that for large distances on N the remainder is small. If P=R^{D-1}xS^{beta}, where S^{beta} is a circle of radius beta, then the result reduces to the well-known approximation of the D dimensional finite temperature quantum field theory to D-1 dimensional one in the high temperature limit. Analytic continuation of Euclidean fields is discussed briefly.Comment: 17 page

Decoupling Solution to SUSY Flavor Problem via Extra Dimensions

We discuss the decoupling solution to SUSY flavor problem in the fat brane scenario. We present a simple model to yield the decoupling sfermion spectrum in a five dimensional theory. Sfermion masses are generated by the overlap between the wave functions of the matter fields and the chiral superfields on the SUSY breaking brane. Two explicit examples of the spectrum are given.Comment: 8 pages, LaTe

Five-dimensional Trinification Improved

We present improved models of trinification in five dimensions. Unified symmetry is broken by a combination of orbifold projections and a boundary Higgs sector. The latter can be decoupled from the theory, realizing a Higgsless limit in which the scale of exotic massive gauge fields is set by the compactification radius. Electroweak Higgs doublets are identified with the fifth components of gauge fields and Yukawa interactions arise via Wilson loops. The result is a simple low-energy effective theory that is consistent with the constraints from proton decay and gauge unification.Comment: 13 pages LaTeX. v2: reference adde

Relativistic diffusive motion in random electromagnetic fields

We show that the relativistic dynamics in a Gaussian random electromagnetic field can be approximated by the relativistic diffusion of Schay and Dudley. Lorentz invariant dynamics in the proper time leads to the diffusion in the proper time. The dynamics in the laboratory time gives the diffusive transport equation corresponding to the Juettner equilibrium at the inverse temperature \beta^{-1}=mc^{2}. The diffusion constant is expressed by the field strength correlation function (Kubo's formula).Comment: the version published in JP

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