title: Dynamical density fluctuations of superfluids near the critical velocity.
abstract: We propose a stability criterion of superfluids in condensed Bose-Einstein systems, which incorporates the spectral function or the autocorrelation function of the local density. Within the Gross-Pitaevskii-Bogoliubov theory, we demonstrate the validity of our criterion for the soliton-emission instability, with use of explicit forms of zero modes of the Bogoliubov equation and a dynamical scaling near the saddle-node bifurcation. We also show that the criterion is applicable to the Landau phonon instability and the Landau roton instability within the single-mode approximation.
authors.affiliation: Department of Basic Science, The University of Tokyo, Tokyo, 153-8902, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kato
authors.forename: Shohei
authors.initials: S
authors.lastname: Watabe