# Stratified Simulations of Collisionless Accretion Disks

## TL;DR

This study uses stratified shearing-box simulations within kinetic MHD to explore how non-gyrotropic pressure influences turbulence and angular-momentum transport in collisionless accretion disks, revealing effects on magnetic reconnection and jet formation.

## Contribution

First to incorporate non-gyrotropic pressure effects into stratified disk simulations, linking kinetic and MHD models and showing impact on turbulence and magnetic field dynamics.

## Key findings

- Non-gyrotropy near current sheets suppresses magnetic reconnection.
- Enhanced turbulence and angular-momentum transport observed with finite non-gyrotropy.
- Results support magnetic field advection crucial for jet launching in black-hole systems.

## Abstract

This paper presents a series of stratified shearing-box simulations of collisionless accretion disks in the recently developed framework of kinetic magnetohydrodynamics (MHD), which can handle finite non-gyrotropy of a pressure tensor. Although a fully kinetic simulation predicted a more efficient angular-momentum transport in collisionless disks than in the standard MHD regime, the enhanced transport has not been observed in past kinetic MHD approaches to gyrotropic pressure anisotropy. For the purpose of investigating this missing link between the fully kinetic and MHD treatments, this paper pays attention to the role of non-gyrotropic pressure, and makes a first attempt to incorporate certain collisionless effects into disk-scale, stratified disk simulations. When the timescale of gyrotropization was longer than, or comparable to, the disk rotation frequency of the orbit, we found that the finite non-gyrotropy selectively remaining in the vicinity of current sheets contributes to suppressing magnetic reconnection in the shearing-box system. This leads to increases both in the saturated amplitude of the MHD turbulence driven by magnetorotational instabilities and in the resultant efficiency of angular-momentum transport. Our results seem favorable for fast advection of magnetic fields toward the rotation axis of a central object, which is required to launch an ultra-relativistic jet from a black-hole accretion system in, for example, a magnetically arrested disk state.