We show that zero-energy flows appear in many particle systems as same as in single particle cases in 2-dimensions. Vortex patterns constructed from the zeroenergy flows can be investigated in terms of the eigenstates in conjugate spaces of Gel'fand triplets. Stable patterns are written by the superposition of zero-energy eigenstates. On the other hand vortex creations and annihilations are described by the insertions of unstable eigenstates with complex-energy eigenvalues into the stable patterns. Some concrete examples are presented in the 2-dimensional parabolic potential barrier case. We point out three interesting properties of the zero-energy flows; (i) the absolute economy as for the energy consumption, (ii) the infinite variety of the vortex patterns, and (iii) the absolute stability of the vortex patterns .Keywords: Zero-energy solutions, vortex creations and annihilations, quantum mechanics, Gel'fand triplets, * E-mail: kobayash@a.tsukuba-tech.ac.jp
IntroductionVortices play interesting roles in various aspects of present-day physics such as vortex matters (vortex lattices) in condensed matters [1,2], quantum Hall effects [3][4][5], various vortex patterns of non-neutral plasma [6][7][8][9] and Bose-Einstein gases [10][11][12][13][14]. Some fundamental properties and applications of vortices in quantum mechanics were examined by many authors [15][16][17][18][19][20][21][22][23].Recently we have proposed a way to investigate vortex patterns in terms of zero-energy solutions of Schrödinger equations in 2-dimensions, which are infinitely degenerate and eigenfunctions in conjugate spaces of Gel'fand triplets (CSGT) [24,25]. It should be noted that the eigenfunctions in CSGT represent scattering states, and thus they are generally not normalizable [26]. Therefore, the probability density (|ψ| 2 ) and the probability current (j = Re[ψ * (−i ∇)ψ]/m) for the eigenfunction (ψ), which are defined in usual Hilbert spaces, cannot be introduced to the eigenfunctions in CSGT. Instead of the probability current, however, the velocity which is defined by v = j/|ψ| 2 can have a well-defined meaning, because the ambiguity due to the normalization of the eigenfunctions disappears in the definition of the velocity. Actually we have shown that many interesting objects used in hydrodynamics such as the complex velocity potential can be introduced in the 2-dimensions of CSGT [27]. We can expect that the hydrodynamical approach is a quite hopeful framework in the investigation of phenomena described in CSGT. One should pay attention to two important facts obtained in the early works [24,25]. One is the fact that the zero-energy solutions are common over the two-dimensional central potentials such that V a (ρ) = −a 2 g a ρ 2(a−1) with ρ = x 2 + y 2 except a = 0 and then similar vortex patters described by the zero-energy solutions appear in all such potentials. Actually zeroenergy solutions for a definite number of a can be transformed to solutions for arbitrary number of a by conformal transformations [24,25]. The oth...