  An idealized "test" object in general relativity moves along a geodesic.
However, if the object has a finite mass, this will create additional curvature
in the spacetime, causing it to deviate from geodesic motion. If the mass is
nonetheless sufficiently small, such an effect is usually treated
perturbatively and is known as the gravitational self-force due to the object.
This issue is still an open problem in gravitational physics today, motivated
not only by basic foundational interest, but also by the need for its direct
application in gravitational-wave astronomy. In particular, the observation of
extreme-mass-ratio inspirals by the future space-based detector LISA will rely
crucially on an accurate modeling of the self-force driving the orbital
evolution and gravitational wave emission of such systems.
  In this paper, we present a novel derivation, based on conservation laws, of
the basic equations of motion for this problem. They are formulated with the
use of a quasilocal (rather than matter) stress-energy-momentum tensor---in
particular, the Brown-York tensor---so as to capture gravitational effects in
the momentum flux of the object, including the self-force. Our formulation and
resulting equations of motion are independent of the choice of the perturbative
gauge. We show that, in addition to the usual gravitational self-force term,
they also lead to an additional "self-pressure" force not found in previous
analyses, and also that our results correctly recover known formulas under
appropriate conditions. Our approach thus offers a fresh geometrical picture
from which to understand the self-force fundamentally, and potentially useful
new avenues for computing it practically.
