We study compact non-supersymmetric Z N orbifolds in various dimensions. We compute the spectrum of several tachyonic type II and heterotic examples and partially classify tachyonfree heterotic models. We also discuss the relation to compactification on K3 and Calabi-Yau manifolds.1 afont@fisica.ciens.ucv.ve 2 ahernand@fis.usb.ve
We investigate the influence of the Coulomb interaction on the adiabatic pumping current through a quantum dot. Using nonequilibrium Green's functions techniques, we derive a general expression for the current based on the instantaneous Green's function of the dot. We apply this formula to study the dependence of the charge pumped per cycle on the time-dependent pumping potentials. Motivated by recent experiments, the possibility of charge quantization in the presence of a finite Coulomb repulsion energy is investigated.
We investigate the low energy continuum limit theory for electrons in a graphene sheet under strain. We use the quantum field theory in curved spaces to analyze the effect of the system deformations into an effective gauge field. We study both in-plane and out-of-plane deformations and obtain a closed expression for the effective gauge field due to arbitrary nonuniform sheet deformations. The obtained results reveal a remarkable relation between the local-pseudo magnetic field and the Riemann curvature, so far overlooked.
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