Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling

Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the ``effective'' Hamiltonian and the ``real'' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pad\'e-resummed coefficients) which depends on the choice of some basic ``effective spin vector'' ${\mathbf{S}}_{\mathrm{eff}}$, and which is deformed by comparable-mass effects; and (iv) an additional effective spin-orbit interaction term involving another spin vector $\mathbit{\ensuremath{\sigma}}$. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter ${\stackrel{^}{a}}_{\mathrm{LSO}}\ensuremath{\equiv}c{J}_{\mathrm{LSO}}/(G({H}_{\mathrm{LSO}}/{c}^{2}{)}^{2})$. We find that the inclusion of NLO spin-orbit terms has a significant ``moderating'' effect on the dynamical characteristics of the circular orbits for large and parallel spins.