We study eigenvalue estimates
of branched Riemannian coverings of compact manifolds. We prove that
if
is a branched Riemannian covering, and {μi}i=0∞ and {λi}i=0∞ are the
eigenvalues of the Laplace-Beltrami operator on M and N, respectively,
then
for all positive t, where k is the number of sheets of the covering. As one application
of this estimate we show that the index of a minimal oriented surface in R3 is
bounded by a constant multiple of the total curvature. Another consequence of
our estimate is that the index of a closed oriented minimal surface in a flat
three-dimensional torus is bounded by a constant multiple of the degree of the Gauss
map.
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