Cherenkov Gravitational Radiation During the Radiation Era
  Cherenkov radiation may occur whenever the source is moving faster than the
waves it generates. In a radiation dominated universe, with equation-of-state
$w = 1/3$, we have recently shown that the Bardeen scalar-metric perturbations
contribute to the linearized Weyl tensor in such a manner that its wavefront
propagates at acoustic speed $\sqrt{w}=1/\sqrt{3}$. In this work, we explicitly
compute the shape of the Bardeen Cherenkov cone and wedge generated
respectively by a supersonic point mass (approximating a primordial black hole)
and a straight Nambu-Goto wire (approximating a cosmic string) moving
perpendicular to its length. When the black hole or cosmic string is moving at
ultra-relativistic speeds, we also calculate explicitly the sudden surge of
scalar-metric induced tidal forces on a pair of test particles due to the
passing Cherenkov shock wave. These forces can stretch or compress, depending
on the orientation of the masses relative to the shock front's normal.
