On the diffusive propagation of warps in thin accretion discs

Understand

In this paper we revisit the issue of the propagation of warps in thin and viscous accretion discs.

• In this regime warps are know to propagate diffusively, with a diffusion coefficient approximately inversely proportional to the disc viscosity.
• Previous numerical investigations of this problem (Lodato & Pringle 2007) did not find a good agreement between the numerical results and the predictions of the analytic theories of warp propagation, both in the linear and in the non-linear case.
• Here, we take advantage of a new, low-memory and highly efficient SPH code to run a large set of very high resolution simulations (up to 20 million SPH particles) of warp propagation, implementing an isotropic disc viscosity in different ways, to investigate the origin of the discrepancy between the theory and the numerical results.