A Precision test for an extra spatial dimension using black-hole-pulsar binaries

We discuss the observable effects of enhanced black hole mass loss in a black hole-neutron star (BH-NS) binary, due to the presence of a warped extra spatial dimension of curvature radius L in the braneworld scenario. For some masses and orbital parameters in the expected ranges the binary components would outspiral-the opposite of the behavior due to energy loss from gravitational radiation alone. If the NS is a pulsar, observations of the rate of change of the orbital period with a precision obtained for the binary pulsar B1913+16 could easily detect the effect of mass loss. For M _BH = 7 M⊙, M _NS = 1.4 M⊙, eccentricity e = 0.1, and L = 10 μm, the critical orbital period dividing systems that inspiral from systems that outspiral is P≈6.5 hr, which is within the range of expected orbital periods; this value drops to P≈4.2 hr for M _BH = 5 M⊙. Observations of a BH-pulsar system could set considerably better limits on L in these braneworld models than could be determined by torsion-balance gravity experiments in the foreseeable future.