94 research outputs found
Variational principle for Hamiltonians with degenerate bottom
We consider perturbations of Hamiltonians whose Fourier symbol attains its
minimum along a hypersurface. Such operators arise in several domains, like
spintronics, theory of supercondictivity, or theory of superfluidity.
Variational estimates for the number of eigenvalues below the essential
spectrum in terms of the perturbation potential are provided. In particular, we
provide an elementary proof that negative potentials lead to an infinite
discrete spectrum.Comment: 9 page
On the Robin eigenvalues of the Laplacian in the exterior of a convex polygon
Let be the exterior of a convex polygon whose
side lengths are . For , let
denote the Laplacian in , , with the Robin boundary
conditions , where is the exterior unit
normal at the boundary of . We show that, for any fixed
, the th eigenvalue of
behaves as E^\Omega_m(\alpha)=-\alpha^2+\mu^D_m
+\mathcal{O}\Big(\dfrac{1}{\sqrt\alpha}\Big) \quad {as $\alpha$ tends to
$+\infty$}, where stands for the th eigenvalue of the operator
and denotes the one-dimensional Laplacian
on with the Dirichlet boundary conditions.Comment: 10 pages. To appear in Nanosystems: Physics, Chemistry, Mathematics.
Minor revision: misprints corrected, references update
Resolvents of self-adjoint extensions with mixed boundary conditions
We prove a variant of Krein's resolvent formula expressing the resolvents of
self-adjoint extensions through the associated boundary conditions.
Applications to solvable quantum-mechanical problems are discussed.Comment: 15 pages, rewritten almost completel
An inequality for the maximum curvature through a geometric flow
We provide a new proof of the following inequality: the maximum curvature
and the enclosed area of a smooth Jordan curve satisfy
. The feature of our proof is the use of the
curve shortening flow.Comment: 2 page
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