Inverse scattering transform for the KPI equation on the background of a one-line soliton

We study the initial value problem of the Kadomtsev-Petviashvili I (KPI) equation with initial data u(x(1), x(2), 0) = u(1) (x(1)) + u(2)(x(1), x(2)), where u(1) (x(1)) is the one-soliton solution of the Korteweg-de Vries equation evaluated at zero time and u(2)(x(1), x(2)) decays sufficiently rapidly on the (x(1), x(2))-plane. This involves the analysis of the nonstationary Schrodinger equation (with time replaced by x(2)) with potential u(x(1), x(2), 0) . We introduce an appropriate sectionally analytic eigenfunction in the complex k-plane where k is the spectral parameter This eigenfunction has the novelty that in addition to the usual jump across the real k-axis, it also has a jump across a segment of the imaginary k-axis. We show that this eigenfunction can be reconstructed through a linear integral equation uniquely defined in terms of appropriate scattering data. In turn, these scattering data are uniquely constructed in terms of u(1)(x(1)) and u(2)(x(1), x(2)). This result implies that the solution of the KPI equation can be obtained through the above linear integral equation where the scattering data have a simple t-dependence.