One-sided type-D Ricci-flat multi-centre metrics

We employ a simplified form of Tod’s ansatz—which is built on the LeBrun–Tod ansatz—to construct one-sided type-D Ricci-flat multi-centre metrics. These metrics are Hermitian non-K{ä}hler and conformally K{ä}hler, and they are determined by a pair of generating potentials: an axisymmetric harmonic function (different from the one originally proposed by Tod) in an auxiliary 3D flat space and its harmonic conjugate. We carry out a systematic study of these multi-centre metrics, including their rod structure, asymptotic structure and recovering from them various known closed-form examples. In particular, we show that, when fitted into the scheme of multi-soliton solutions on flat space constructed by the present author using the inverse-scattering method, these metrics, with number of centres $n\le 3$, have a free-soliton number 2 or 3 greater than their phantom-soliton number; we conjecture that this is true for general $n$.