Landau Damping of Baryon Structure Formation in the Post Reionization Epoch

TL;DR

This paper investigates how Landau damping affects baryon structure formation after reionization, highlighting the suppression of baryon density fluctuations at small scales due to plasma collective effects.

Contribution

It extends the Chen-Lai model by incorporating Landau damping of ion-acoustic oscillations, providing a more accurate description of baryon density spectrum suppression.

Findings

Landau damping significantly suppresses baryon density fluctuations at high wavenumbers.

Modification of the filtering wavenumber improves the model's accuracy.

Potential observability of Landau damping effects at high redshifts.

Abstract

It has been suggested by Chen and Lai that the proper description of the large scale structure formation of the universe in the post-reionization era, which is conventionally characterized via gas hydrodynamics, should include the plasma collective effects in the formulation. Specifically, it is the combined pressure from the baryon thermal motions and the residual long-range electrostatic potentials resulted from the imperfect Debye shielding, that fights against the gravitational collapse. As a result, at small-scales the baryons would oscillate at the ion-acoustic, instead of the conventional neutral acoustic, frequency. In this paper we extend and improve the Chen-Lai formulation with the attention to the Landau damping of the ion-acoustic oscillations. Since T_e \sim T_i in the post-reionization era, the ion acoustic oscillations would inevitably suffer the Landau damping which severely suppresses the baryon density spectrum in the regimes of intermediate and high wavenumber k. To describe this Landau-damping phenomenon more appropriately, we find it necessary to modify the filtering wavenumber k_f in our analysis. It would be interesting if our predicted Landau damping of the ion-acoustic oscillations can be observed at high redshifts.