Canad. Math. Bull. 53(2010), 737-745
Printed: Dec 2010
A new and elementary proof is given of the recent result of Cuccagna, Pelinovsky,
and Vougalter based on the variational principle for the
quadratic form of a self-adjoint operator.
It is the negative index theorem for a linearized NLS operator in
35Q55 - NLS-like equations (nonlinear Schrodinger) [See also 37K10]
81Q10 - Selfadjoint operator theory in quantum theory, including spectral analysis