Constraints on fourth order gravity from binary pulsars and gravitational waves

Abstract

We have earlier proposed a fourth order gravity model as a possible explanation for late time cosmic acceleration, and for flattened galaxy rotation curves. The model has a free length parameter whose value depends on the scale of the system under study (e.g. the whole Universe, a galaxy, or a compact binary pulsar). In the present work, we investigate the constraints imposed on the free model parameter by Hulse-Taylor binary pulsar data: periastron advance; and emission of gravitational waves and consequent period decay. It is shown that the model is consistent with these observations, provided the length parameter is bounded from above.

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“…Similarly, we also assume that the local equation of motion for gravitational waves also holds modulo the timevarying coupling, and hence we describe models that still have second-order derivative equations of motion (see e.g. [41] for a similar analysis in a model with higher derivatives). We thus start by considering the standard linearized Einstein equations in the Lorentz gauge with a G gw (t), valid in the weak field regime:…”

“…In this analysis, we will assume that the only non-trivial effect in the motion of the binaries is due to the presence of a timevarying G N . Similarly, we also assume that the local equation of motion for gravitational waves also holds modulo the timevarying coupling, and hence we describe models that still have second-order derivative equations of motion (see e.g [41]. for1 Note that the exact calculation of the quadratic interactions of the metric around a local background has not been performed in detail in the literature, but from eq.…”