Title: Cosmic Ray Transport and Feedback in Galaxies and Clusters

Abstract: Relativistic cosmic rays may play an important role in the evolution of gas in galaxies and clusters by driving outflows and heating diffuse gas.  However, the impact of cosmic rays is a very strong function of their transport, which remains uncertain. In this talk, I will discuss theoretical uncertainties in cosmic ray propagation, and how cosmic ray spectra measured at Earth help us constrain their transport. I will then use a plausible mode of transport to consider the impact of cosmic rays on the intra-cluster medium (ICM) in galaxy clusters. In particular, I will demonstrate that cosmic rays can efficiently excite waves, which may subsequently travel and dissipate across the ICM. This has potentially significant implications for the long-standing puzzle of how thermal balance is maintained in the cores of galaxy clusters.