Linear operator theory of phase mixing

ABSTRACT We study solutions of the collisionless Boltzmann equation (CBE) in a functional Koopman representation. This facilitates the use of linear spectral techniques characteristic of the analysis of Schrödinger-type equations. For illustrative purposes, we consider the classical phase mixing of...

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Veröffentlicht in:Monthly notices of the Royal Astronomical Society Jg. 533; H. 1; S. 79 - 92
Hauptverfasser: Darling, Keir, Widrow, Lawrence M
Format: Journal Article
Sprache:Englisch
Veröffentlicht: London Oxford University Press 01.09.2024
Schlagworte:
Boltzmann transport equation
Distribution functions
Eigenvalues
Harmonic oscillators
Linear operators
Representations
Schrodinger equation
Spectral methods
Subspaces
System dynamics
Galaxy: structure
Galaxy: kinematics and dynamics
Galaxy: disc
ISSN:0035-8711, 1365-2966
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Zusammenfassung:ABSTRACT We study solutions of the collisionless Boltzmann equation (CBE) in a functional Koopman representation. This facilitates the use of linear spectral techniques characteristic of the analysis of Schrödinger-type equations. For illustrative purposes, we consider the classical phase mixing of a non-interacting distribution function in a quartic potential. Solutions are determined perturbatively relative to a harmonic oscillator. We impose a form of coarse-graining by choosing a finite-dimensional basis to represent the distribution function and time evolution operators, which sets a minimum length-scale on phase space structure. We observe a relationship between the dimension of the representation and the multiplicity of the harmonic oscillator eigenvalues. System dynamics are understood in terms of degenerate subspaces of the linear operator spectra. Each subspace is associated with a mode of the harmonic oscillator, the first two being bending and breathing structures. The quartic potential splits the degenerate eigenvalues within each subspace. This facilitates the formation of spiral structure as deformations from the harmonic oscillator modes. We ultimately argue that this construction provides a promising avenue for study of self-interacting systems experiencing phase mixing, which is an outstanding problem in the context of the Gaia DR2 vertical phase space spirals.
Bibliographie:ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 14
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stae1775