6,450 research outputs found
Bloch bundles, Marzari-Vanderbilt functional and maximally localized Wannier functions
We consider a periodic Schroedinger operator and the composite Wannier
functions corresponding to a relevant family of its Bloch bands, separated by a
gap from the rest of the spectrum. We study the associated localization
functional introduced by Marzari and Vanderbilt, and we prove some results
about the existence and exponential localization of its minimizers, in
dimension d < 4. The proof exploits ideas and methods from the theory of
harmonic maps between Riemannian manifolds.Comment: 37 pages, no figures. V2: the appendix has been completely rewritten.
V3: final version, to appear in Commun. Math. Physic
Polynomial cubic differentials and convex polygons in the projective plane
We construct and study a natural homeomorphism between the moduli space of
polynomial cubic differentials of degree d on the complex plane and the space
of projective equivalence classes of oriented convex polygons with d+3
vertices. This map arises from the construction of a complete hyperbolic affine
sphere with prescribed Pick differential, and can be seen as an analogue of the
Labourie-Loftin parameterization of convex RP^2 structures on a compact surface
by the bundle of holomorphic cubic differentials over Teichmuller space.Comment: 64 pages, 5 figures. v3: Minor revisions according to referee report.
v2: Corrections in section 5 and related new material in appendix
Equivariant self-similar wave maps from Minkowski spacetime into 3-sphere
We prove existence of a countable family of spherically symmetric
self-similar wave maps from 3+1 Minkowski spacetime into the 3-sphere. These
maps can be viewed as excitations of the ground state wave map found previously
by Shatah. The first excitation is particularly interesting in the context of
the Cauchy problem since it plays the role of a critical solution sitting at
the threshold of singularity formation. We analyze the linear stability of our
wave maps and show that the number of unstable modes about a given map is equal
to its excitation index. Finally, we formulate a condition under which these
results can be generalized to higher dimensions.Comment: 15 pages, extended version to appear in Comm. Math. Phy
Triunduloids: Embedded constant mean curvature surfaces with three ends and genus zero
In 1841, Delaunay constructed the embedded surfaces of revolution with
constant mean curvature (CMC); these unduloids have genus zero and are now
known to be the only embedded CMC surfaces with two ends and finite genus.
Here, we construct the complete family of embedded CMC surfaces with three ends
and genus zero; they are classified using their asymptotic necksizes. We work
in a class slightly more general than embedded surfaces, namely immersed
surfaces which bound an immersed three-manifold, as introduced by Alexandrov.Comment: LaTeX, 22 pages, 2 figures (8 ps files); full version of our
announcement math.DG/9903101; final version (minor revisions) to appear in
Crelle's J. reine angew. Mat
Effectively Closed Infinite-Genus Surfaces and the String Coupling
The class of effectively closed infinite-genus surfaces, defining the
completion of the domain of string perturbation theory, can be included in the
category , which is characterized by the vanishing capacity of the ideal
boundary. The cardinality of the maximal set of endpoints is shown to be
2^{\mit N}. The product of the coefficient of the genus-g superstring
amplitude in four dimensions by in the limit is an
exponential function of the genus with a base comparable in magnitude to the
unified gauge coupling. The value of the string coupling is consistent with the
characteristics of configurations which provide a dominant contribution to a
finite vacuum amplitude.Comment: TeX, 33 page
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