2,387 research outputs found
Ferromagnetism in the Hubbard model with Topological/Non-Topological Flat Bands
We introduce and study two classes of Hubbard models with magnetic flux or
with spin-orbit coupling, which have a flat lowest band separated from other
bands by a nonzero gap. We study the Chern number of the flat bands, and find
that it is zero for the first class but can be nontrivial in the second. We
also prove that the introduction of on-site Coulomb repulsion leads to
ferromagnetism in both the classes.Comment: 6 pages, 5 figure
On the chiral anomaly in non-Riemannian spacetimes
The translational Chern-Simons type three-form coframe torsion on a
Riemann-Cartan spacetime is related (by differentiation) to the Nieh-Yan
four-form. Following Chandia and Zanelli, two spaces with non-trivial
translational Chern-Simons forms are discussed. We then demonstrate, firstly
within the classical Einstein-Cartan-Dirac theory and secondly in the quantum
heat kernel approach to the Dirac operator, how the Nieh-Yan form surfaces in
both contexts, in contrast to what has been assumed previously.Comment: 18 pages, RevTe
Inflation, bifurcations of nonlinear curvature Lagrangians and dark energy
A possible equivalence of scalar dark matter, the inflaton, and modified
gravity is analyzed. After a conformal mapping, the dependence of the effective
Lagrangian on the curvature is not only singular but also bifurcates into
several almost Einsteinian spaces, distinguished only by a different effective
gravitational strength and cosmological constant. A swallow tail catastrophe in
the bifurcation set indicates the possibility for the coexistence of different
Einsteinian domains in our Universe. This `triple unification' may shed new
light on the nature and large scale distribution not only of dark matter but
also on `dark energy', regarded as an effective cosmological constant, and
inflation.Comment: 20 pages, 8 figures, Proceedings of the 11th Marcel Grossmann Meeting
(MG11) in Berlin, Germany, July 23-29, 200
Flat-Bands on Partial Line Graphs -- Systematic Method for Generating Flat-Band Lattice Structures
We introduce a systematic method for constructing a class of lattice
structures that we call ``partial line graphs''.In tight-binding models on
partial line graphs, energy bands with flat energy dispersions emerge.This
method can be applied to two- and three-dimensional systems. We show examples
of partial line graphs of square and cubic lattices. The method is useful in
providing a guideline for synthesizing materials with flat energy bands, since
the tight-binding models on the partial line graphs provide us a large room for
modification, maintaining the flat energy dispersions.Comment: 9 pages, 4 figure
Preserving and Enhancing Access to Non-Commercial Sound Recordings at The Harry Ransom Center
The Harry Ransom Center at The University of Texas at Austin requests funds to support a $35,132 one-year project to develop and complete a preservation survey of the Center’s archival sound recordings. This survey will establish, enhance, and document preservation digitization priorities, processes, and standards to ensure future access to a significant collection of primary research materials
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