Probing Gravitational Parity Violation with Gravitational Waves from
  Stellar-mass Black Hole Binaries
  The recent discovery of gravitational wave events has offered us unique
testbeds of gravity in the strong and dynamical field regime. One possible
modification to General Relativity is the gravitational parity violation that
gives rise to the amplitude birefringence in gravitational waves, where one of
the circularly-polarized mode is amplified while the other one is suppressed
during their propagation. In this paper, we study how well one can measure
gravitational parity violation via the amplitude birefringence of gravitational
waves from stellar-mass black hole binaries. We choose Chern-Simons gravity as
an example and work within an effective field theory formalism. We consider
gravitational waves from both individual sources and stochastic gravitational
wave backgrounds. Regarding bounds from individual sources, we estimate them
using a Fisher analysis and carry out Monte Carlo simulations by randomly
distributing sources over their sky location and binary orientation. We find
that the bounds on the scalar field evolution in Chern-Simons gravity from
GW150914 are too weak to satisfy the weak Chern-Simons approximation, while
aLIGO with its design sensitivity can place meaningful bounds. Regarding bounds
from stochastic gravitational wave backgrounds, we set the threshold
signal-to-noise ratio for detection of the parity-violation mode as 5 and
estimate projected bounds with future detectors assuming that signals are
consistent with no parity violation. We find that a network of two
third-generation detectors is able to place bounds that are slightly stronger
than current binary pulsar bounds. Since gravitational wave observations probe
either the difference in parity violation between the source and the detector
or the line-of-sight integration of the scalar field, such bounds are
complementary to local measurements from solar system experiments and binary
pulsar observations.
