Now we list some features of our 3 PN equations of motion. In the test-particle limit, our 3 PN
equations of motion coincide with a geodesic equation for a test-particle in the Schwarzschild metric in
harmonic coordinates (up to 3 PN order). Suppose that star is a test particle, star
is represented
by the Schwarzschild metric, and
. Then the geodesic equation for star
becomes
With the help of the formulas developed in [28], we have checked the Lorentz invariance of
Equation (181) (in the post-Newtonian perturbative sense). Also, we have checked that our
3 PN acceleration admits a conserved energy of the binary orbital motion (modulo the 2.5 PN
radiation reaction effect). In fact, the energy
of the binary associated with Equation (181
) is
We note that Equation (171) as well gives a correct geodesic equation in the test-particle limit, is
Lorentz invariant, and admits the conserved energy. These facts can be seen by the form of
, Equation (175
); it is zero when
, is Lorentz invariant up to 3 PN order,
and is the effect of the mere redefinition of the dipole moments which does not break energy
conservation.
Finally, we here mention one computational detail. We have retained during our calculation
-dependent terms with positive powers of
or logarithms of
. As stated below Equation (76
), it
is a good computational check to show that our equations of motion do not depend on
physically. In
fact, we found that the
-dependent terms cancel each other out in the final result. There is no
need to employ a gauge transformation to remove such an
dependence. As for terms with
negative powers of
, we simply assume that those terms cancel out the
dependent
terms from the far zone contribution. Indeed, Pati and Will [129
, 130
], whose method we have
adopted to compute the far zone contribution, have proved that all the
-dependent terms
cancel out between the far zone and the near zone contributions through all post-Newtonian
orders.
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