Testing local Lorentz invariance of gravity with binary-pulsar data

As gravity is a long-range force, one might a priori expect the Universe’s global matter distribution to select a preferred rest frame for local gravitational physics. Two parameters ${\mathrm{\alpha }}_1$ and ${\mathrm{\alpha }}_2$ suffice to describe the phenomenology of preferred-frame effects on post-Newtonian gravity. One of them has already been very tightly constrained (‖${\mathrm{\alpha }}_2$‖<2.4×${10}^{\mathrm{-}7}$). We show here that binary-pulsar data provide a bound on the other one (‖${\mathrm{\alpha }}_1$‖<5.0×${10}^{\mathrm{-}4}$, 90% C.L.) which is quantitatively comparable to previous solar-system limits, but qualitatively more powerful because it is derived for systems comprising strong-gravitational-field regions. Our results correct a previous claim that ${\mathrm{\alpha }}_1$ could be very tightly constrained via a purported semisecular effect in the orbital period of binary pulsars.