Testing the gravitational weak equivalence principle in the standard model extension with binary pulsars

Abstract

The Standard-Model Extension provides a framework to systematically investigate possible violation of the Lorentz symmetry. Concerning gravity, the linearized version was extensively examined. We here cast the first set of experimental bounds on the nonlinear terms in the field equation from the anisotropic cubic curvature couplings. These terms introduce body-dependent accelerations for self-gravitating objects, thus violating the gravitational weak equivalence principle (GWEP). Novel phenomena, that are absent in the linearized gravity, remain experimentally unexplored. We constrain them with precise binary-orbit measurements from pulsar timing, wherein the high density and large compactness of neutron stars are crucial for the test. It is the first study that seeks GWEP-violating signals in a fully anisotropic framework with Lorentz violation.

Neutron star structure in the minimal gravitational Standard-Model Extension and the implication to continuous gravitational waves

“…Introducing the Lorentz-violation coefficients makes the SME framework practically useful by allowing experiments to test the coefficients without worrying arXiv:1909.10372v1 [gr-qc] 23 Sep 2019 about the dynamics of the corresponding fields as long as gravity is weak [18,37,38]. A large amount of constraints have been put on the Lorentz-violation coefficients from various terrestrial experiments [39][40][41][42] and astrophysical observations [32,34,[43][44][45][46][47][48][49][50] that assume the validity of weak gravity.…”

Lorentz-Violating Matter-Gravity Couplings in Small-Eccentricity Binary Pulsars

“…The pure-gravity sector of the SME at different mass dimensions was systematically tested with binary pulsars in Refs. [21][22][23][24]. Early limits on (a w eff ) k were given with K/He magnetometer and torsion-strip balance [42,43]; but these limits, while constraining different linear combinations of the Lorentz violating coefficients, are rather weak.…”

“…Nevertheless, when people start to discover some evidence for the Lorentz violation, it is absolutely needed to take into account more sophisticated analysis, for example, to use the 3-D orientation of the orbit (possibly in a probabilistic way with an unknown Ω) as was done in Refs. [21][22][23][24]. In addition, if one wants to explore the correlation between different coefficients for Lorentz violation, more sophisticated analysis is needed as well.…”

“…Specifically, even pessimistically assuming no advance in the quality of binary-pulsar observation for the future, the tests in Eqs. (24)(25)(26) improve as T −1.5 obs where T obs is the total observational span. In reality, the quality of observation improves rapidly, especially with the newly built and upcoming telescopes, like the Five-hundred-meter Aperture Spherical Telescope (FAST), the MeerKAT telescope, and the Square Kilometre Array (SKA) [58][59][60][61].…”

Maximal Tests in Minimal Gravity

“…Study of the nonminimal gravity sector beyond the linearized limit has also begun. 21,22 In addition to work aimed directly at seeking signals of Lorentz violation in experiments, several theory-oriented results deserve discussion in this context. While it is difficult to capture the volume of work done in this area in this short summary, examples discussed in these proceedings include exploration of specific Lorentz-violating models that generate nonzero SME coefficients 23,24 and the implications of geometric constraints on Lorentz violation.…”