Spacetime as a topological insulator: Mechanism for the origin of the fermion generations

We suggest a mechanism whereby the three generations of quarks and leptons correspond to surface modes in a five-dimensional theory. These modes arise from a nonlinear fermion dispersion relation in the extra dimension, much in the same manner as fermion surface modes in a topological insulator or lattice implementation of domain wall fermions. We also show that the topological properties can persist in a deconstructed version of the model in four dimensions.Comment: Substantially revised version, to appear in Phys. Rev. Let

Thermoelectric properties of nn-type SrTiO3

We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high $ZT$ at optimized doping, and suggests that the $ZT$ value can reach 0.7 at T = 1400 K. Thus $ZT$ can be improved from the current experimental values by carrier concentration optimization

COBE's Constraints on the Global Monopole and Texture Theories of Cosmic Structure Formation

We report on a calculation of large scale anisotropy in the cosmic microwave background radiation in the global monopole and texture models for cosmic structure formation. We have evolved the six component linear gravitational field along with the monopole or texture scalar fields numerically in an expanding universe and performed the Sachs-Wolfe integrals directly on the calculated gravitational fields. On scales $> 7^\circ$, we find a Gaussian distribution with an approximately scale invariant fluctuation spectrum. The $\Delta T/T$ amplitude is a factor of 4-5 larger than the prediction of the standard CDM model with the same Hubble constant and density fluctuation normalization. The recently reported COBE-DMR results imply that global monopole and texture models require high bias factors or a large Hubble constant in contrast to standard CDM which requires very low $H_0$ and bias values. For $H_0 = 70 {\rm {km\over sec} Mpc^{-1}}$, we find that normalizing to the COBE results implies $b_8 \simeq 3.2\pm 1.4$ (95\% c.l.). If we restrict ourselves to the range of bias factors thought to be reasonable before the announcement of the COBE results, 1.5 \lsim b_8 \lsim 2.5, then it is fair to conclude that global monopoles and textures are consistent with the COBE results and are a {\it better} fit than Standard CDM.Comment: 8 pages, 5 figures (not included, but available by mail), CfPA-TH-92-2