Sixth post-Newtonian local-in-time dynamics of binary systems

Using a recently introduced method Phys. \ Rev. \ Lett. \ 123, 231104 (2019), which splits the conservative dynamics of gravitationally interacting binary systems into a non-local-in-time part and a local-in-time one, we compute the local part of the dynamics at the sixth post-Newtonian (6PN) accuracy. Our strategy combines several theoretical formalisms: post-Newtonian, post-Minkowskian, multipolar-post-Minkowskian, effective-field-theory, gravitational self-force, effective one-body, and Delaunay averaging. The full functional structure of the local 6PN Hamiltonian (which involves 151 numerical coefficients) is derived, but contains four undetermined numerical coefficients. Our 6PN-accurate results are complete at orders G³ and G⁴, and the derived O (G³) scattering angle agrees, within our 6PN accuracy, with the computation of Phys. \ Rev. \ Lett. \ 122, no. 20, 201603 (2019). All our results are expressed in several different gauge-invariant ways. We highlight, and make a crucial use of, several aspects of the hidden simplicity of the mass-ratio dependence of the two-body dynamics.