  We study nodal librations of outer particles in the framework of the
elliptical restricted three-body problem including general relativity (GR)
effects. From an analytical treatment based on secular interactions up to
quadrupole level, we derive equations that define the nodal libration region of
an outer test particle, which depends on the physical and orbital parameters of
the bodies of the system. From this, we analyze how the GR constrains the
semimajor axis of outer test particles that experience nodal librations under
the effects of an inner planet around a single stellar component. Such an upper
limit of the semimajor axis, which is called a2,lim , depends on the mass of
the star ms, the mass m1, the semimajor axis a1, and the eccentricity e1 of the
inner planet, and the eccentricity e2 of the outer test particle. On the one
hand, our results show that the greater m1, a1, and e2 and the smaller ms, the
greater the value of a2,lim. On the other hand, for fixed ms, m1, a1, and e2,
a2,lim does not strongly depend on e1, except for large values of such an
orbital parameter. We remark that N-body experiments of particular scenarios
that include GR show results consistent with the analytical criteria derived in
the present research. Moreover, the study of hypothetical small body
populations of real systems composed of a single star and an inner
planetary-mass companion show that the GR effects can play a very important
role in their global dynamics.
