Implications, Tests, and Unsolved Problems in Cosmic Ray Feedback

Cosmic rays, the relativistic component of diffuse astrophysical plasma, exchange energy and momentum with the thermal gas collisionlessly, mediated by the ambient magnetic field. Some but not all models of this interaction show that cosmic rays can drive outflows, heat the gas, and reduce the star formation rate in galactic disks. I will probe the properties of these models and their implications on small scales, discuss consequences that may be observable, and highlight a few unsolved problems.