  We explore various aspects of the motion of heavy quarks in strongly-coupled
gauge theories, employing the AdS/CFT correspondence. Building on earlier work
by Mikhailov, we study the dispersion relation and energy loss of an
accelerating finite-mass quark in N=4 super-Yang-Mills, both in vacuum and in
the presence of a thermal plasma. In the former case, we notice that the
application of an external force modifies the dispersion relation. In the
latter case, we find in particular that when a static heavy quark is
accelerated by an external force, its rate of energy loss is initially
insensitive to the plasma, and there is a delay before this rate approaches the
value derived previously from the analysis of stationary or late-time
configurations.
  Following up on work by Herzog et al., we also consider the evolution of a
quark and antiquark as they separate from one another after formation, learning
how the AdS/CFT setup distinguishes between the singlet and adjoint
configurations, and locating the transition to the stage where the deceleration
of each particle is properly accounted for by a constant friction coefficient.
Additionally, we examine the way in which the energy of a quark-antiquark pair
moving jointly through the plasma scales with the quark mass. We find that the
velocity-dependence of the screening length is drastically modified in the
ultra-relativistic region, and is comparable with that of the transition
distance mentioned above.
