Perturbative Analytical Construction of Bowen–York Initial Data for Binary Black Holes up to Third Order in Spin and Linear Momentum

ABSTRACT We analytically construct initial data for binary black hole systems by solving the Einstein constraint equations within the Bowen–York framework. Allowing for arbitrarily oriented linear momenta and spins, we obtain a perturbative solution of the vacuum Hamiltonian constraint up to third order in the source parameters. Our solution explicitly incorporates the system's binary nature via position‐weighted multipole moments. The momentum constraints are solved exactly, while the conformal factor is determined analytically. Using the resulting initial data, we compute the ADM energy, linear and angular momenta, and the irreducible mass. We also determine the shape of the apparent horizon and show that it is geometrically consistent with the inner‐end regularity. The resulting expressions are written in a manifestly tensorial form and provide an analytic benchmark for numerical–relativity calculations within the perturbative far‐zone regime considered here.