Long-lived N-body disks
Many of the same physical processes drive the evolution of circumstellar discs composed of dust grains, asteroids, planetesimals, planets, etc. This talk investigates the survival of such discs over Gyr timescales, using a unified approach that is applicable to all Keplerian discs of solid bodies. Monodisperse discs can be characterized locally by four parameters: surface density, semi-major axis, velocity dispersion, and size of the bodies. For a given set of these parameters, the disc must survive all dynamical processes, including gravitational instability, dynamical chaos, gravitational scattering, physical collisions, and radiation forces, that would lead to significant evolution over its lifetime. These processes lead to a rich set of constraints that strongly restrict the possible properties of long-lived discs. Within this framework, I also discuss the detection of planetesimal discs using radial velocity measurements, transits, microlensing, and the infrared emission from the planetesimals themselves or from dust generated by planetesimal collisions. A wide range of long-lived discs would not have been detected by present techniques.