  Electron and ion energization (i.e., heating and nonthermal acceleration) is
a fundamental, but poorly understood, outcome of plasma turbulence. In this
work, we present new results on this topic from particle-in-cell simulations of
driven turbulence in collisionless, relativistic electron-ion plasma. We focus
on temperatures such that ions (protons) are sub-relativistic and electrons are
ultra-relativistic, a regime relevant for high-energy astrophysical systems
such as hot accretion flows onto black holes. We find that ions tend to be
preferentially heated, gaining up to an order of magnitude more energy than
electrons, and propose a simple empirical formula to describe the electron-ion
energy partition as a function of the ratio of electron-to-ion gyroradii (which
in turn is a function of initial temperatures and plasma beta). We also find
that while efficient nonthermal particle acceleration occurs for both species
in the ultra-relativistic regime, nonthermal electron populations are
diminished with decreasing temperature whereas nonthermal ion populations are
essentially unchanged. These results have implications for modeling and
interpreting observations of hot accretion flows.
