A different class of theories, allowing a non-linear coupling
between matter and a scalar field, was later studied by Damour
and Esposito-Farèse [35,
37]. The function coupling the scalar field
to matter is given by
, and the theories are described by the parameters
and
, where
is the value that
approaches at spatial infinity (cf.
Section
3.3). These theories allow significant strong-field effects when
is negative, even if the weak-field limit is small. They are
best tested by combining results from PSRs B1913+16,
B1534+12 (which contributes little to this test), B0655+64
(limits on dipolar gravitational radiation), and solar-system
experiments (Lunar laser ranging, Shapiro delay measured by
Viking [116], and the perihelion advance of Mercury [118]). The allowed parameter space from the combined tests is shown
graphically in Figure
10
[37
]. Currently, for most neutron-star equations of state, the
solar-system tests set a limit on
(
) that is a few times more stringent than those set by
PSRs B1913+16 and B0655+64, although the pulsar observations
do eliminate large negative values of
. With the limits from the pulsar observations improving only
very slowly with time, it appears that solar-system tests will
continue to set the strongest limits on
in this class of theories, unless a pulsar-black-hole system is
discovered. If such a system were found with a
-
black hole and an orbital period similar to that of
PSR B1913+16 (
hours), the limit on
derived from this system would be about 50 times tighter than
that set by current solar-system tests, and 10 times better than
is likely to be achieved by the Gravity Probe B
experiment [37
].
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Testing General Relativity with Pulsar Timing
Ingrid H. Stairs http://www.livingreviews.org/lrr-2003-5 © Max-Planck-Gesellschaft. ISSN 1433-8351 Problems/Comments to livrev@aei-potsdam.mpg.de |