  The class of Galileon scalar fields theories encapsulate the Vainshtein
screening mechanism which is characteristic of a large range of infrared
modified theories of gravity. Such theories can lead to testable departures
from General Relativity through fifth forces and new scalar modes of
gravitational radiation. However, the inherent non-linearity of the Vainshtein
mechanism has limited analytic attempts to describe Galileon theories with both
cubic and quartic interactions. To improve on this, we perform direct numerical
simulations of the quartic Galileon model for a rotating binary source and
infer the power spectrum of given multipoles. To tame numerical instabilities
we utilize a low-pass filter, extending previous work on the cubic Galileon.
Our findings show that the multipole expansion is well-defined and under
control. Moreover, our results confirm that despite being a non-linear scalar,
the dominant Galileon radiation is quadrupole, and we find a new scaling
behaviour deep inside the Vainshtein region.
