Model-independent comparisons of pulsar timings to scalar–tensor gravity
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abstract
Observations of pulsar timing provide strong constraints on scalar-tensor
theories of gravity, but these constraints are traditionally quoted as limits
on the microscopic parameters (like the Brans-Dicke coupling, for example) that
govern the strength of scalar-matter couplings at the particle level in
particular models. Here we present fits to timing data for several pulsars
directly in terms of the phenomenological couplings (masses, scalar charges,
moment of inertia sensitivities and so on) of the stars involved, rather than
to the more microscopic parameters of a specific model. For instance, for the
double pulsar PSR J0737-3039A/B we find at the 68% confidence level that the
masses are bounded by 1.28 < m_A/m_sun < 1.34 and 1.19 < m_B/m_sun < 1.25,
while the scalar-charge to mass ratios satisfy |a_A| < 0.21, |a_B| < 0.21 and
|a_B - a_A| < 0.002$. These constraints are independent of the details of the
scalar tensor model involved, and of assumptions about the stellar equations of
state. Our fits can be used to constrain a broad class of scalar tensor
theories by computing the fit quantities as functions of the microscopic
parameters in any particular model. For the Brans-Dicke and quasi-Brans-Dicke
models, the constraints obtained in this manner are consistent with those
quoted in the literature.
