4.5 Post-Newtonian order gravitational radiation

International audiencePost-Newtonian (PN) theory enables us to predict the waveform and the phaseevolution of the gravitational waves emitted by a system of two compact objectscoalescing in its inspiral phase. State-of-the-art works provide the phase ofthe expected signal up to 3.5PN 5 (i.e. up to 1/c 7). Comparison with numericalrelativity, as well as the promising evolution of gravitational wave detectorsand the new discoveries incite us to pursue this computation to a higher order.In our current program, we are aiming at reaching the phase of the signal at the4.5PN order (i.e. 1/c 9). For this purpose, the energy flux emitted by such asystem for circular orbits has to be known at 4.5PN. One difficulty of thiscomputation is the high-order interactions-commonly called tails-between themass of the system and its mass and current multipole moments during thepropagation of the signal. In Marchand et al. 2016 1 , we have computed thecontribution of all the tails entering the flux at the 4.5PN order, and inparticular the third-order mass-quadrupole interactions known as " tails-of-tails-of-tails ". Our work enables to fully determine the 4.5PN coefficient ofthe flux for circular orbits (while the 4PN coefficient is still unknown)