No Slip Gravity
  A subclass of the Horndeski modified gravity theory we call No Slip Gravity
has particularly interesting properties: 1) a speed of gravitational wave
propagation equal to the speed of light, 2) equality between the effective
gravitational coupling strengths to matter and light, $G_{\rm matter}$ and
$G_{\rm light}$, hence no slip between the metric potentials, yet difference
from Newton's constant, and 3) suppressed growth to give better agreement with
galaxy clustering observations. We explore the characteristics and implications
of this theory, and project observational constraints. We also give a simple
expression for the ratio of the gravitational wave standard siren distance to
the photon standard candle distance, in this theory and others, and enable a
direct comparison of modified gravity in structure growth and in gravitational
waves, an important crosscheck.
