Quasistationary states in the self-gravitating sheet model

Area of Science:

• Astrophysical plasma physics
• Statistical mechanics
• Computational physics

Background:

• Quasistationary states (QSSs) are long-lived, non-equilibrium states observed in collisionless self-gravitating systems.
• Violent relaxation is a key mechanism driving systems towards QSSs.
• Lynden-Bell (LB) theory provides a theoretical framework for describing these states.

Purpose of the Study:

• To assess the validity of Lynden-Bell theory in describing QSSs within the one-dimensional self-gravitating sheet model.
• To investigate the influence of initial conditions on the accuracy of LB predictions.
• To explore the emergence of degenerate core-halo structures when LB theory fails.

Main Methods:

• Simulations of the one-dimensional self-gravitating sheet model with varying "waterbag" initial conditions.
• Analysis of quasistationary states resulting from violent relaxation.
• Comparison of simulation results with Lynden-Bell theory predictions.

Main Results:

• Lynden-Bell theory predictions are accurate for low-energy initial conditions.
• At higher energies (nondegenerate limit), LB theory predictions become qualitatively incorrect for most initial conditions.
• Failure of LB theory correlates with the formation of a degenerate core-halo structure, attributed to dynamical resonances.

Conclusions:

• Lynden-Bell theory is a good approximation for QSSs only when violent relaxation is sufficiently gentle.
• Degenerate core-halo structures emerge in more energetic systems where LB theory is inadequate.
• The study highlights the limitations of LB theory and the importance of initial conditions in determining QSS properties.