Constraints on non-local gravity from binary pulsars gravitational emission

Abstract

Non-local theories of gravity are considered extended theories of gravity, meaning that when the non-local terms are canceled out, the limit of General Relativity (GR) is obtained. Several reasons have led us to consider this theory with increasing interest, but primarily non-locality emerges in a natural way as a ‘side’ effect of the introduction of quantum corrections to GR, the purpose of which was to cure the singularity problem, both at astrophysical and cosmological level. In this paper we studied a peculiar case of the so called Deser-Woodard theory consisting in the addition of a non-local term of the form R□−1R to the Hilbert-Einstein lagrangian, where R is the Ricci scalar, and derived, for the first time, constraints on the dimensionaless non-local parameter A by exploiting the predicted gravitational wave emission in three binary pulsars, namely PSR J1012+5307, PSR J0348+0432 and PSR J1738+0333. We discovered that the instantaneous flux strongly depends on A and that the best constraints (0.12<A<0.16) come from PSR J1012+5307, for which the GR prediction is outside the observational ranges. However, since for PSR J1012+5307 scintillation is suspected, as emerged in a recent census by LOFAR corruptions in pulsar timing could be hidden. We finally comment on the usability and reliability of this type of test for extended theories of gravity.