Focusing and defocusing mKdV equation with fully asymmetric nonzero boundary conditions: the inverse scattering transform

Abstract: In this paper, we investigate the inverse scattering transform(IST) for the focusing and defocusing mKdV equation with fully asymmetric nonzero boundary conditions. Our analysis focuses on the properties of the Jost function, allowing us to establish the associated Riemann-Hilbert (RH) problem for both the focusing and defocusing cases. Furthermore, we recover the potential from the RH problem, which plays a crucial role in calculating the long-time asymptotic behavior of the solution. In the symmetric case, the eigenvalues are given by $\lambda^2 = k^2 \pm q_0^2$. However, in the asymmetric case, the eigenvalues are represented as $\lambda_\pm^2 = k^2 \pm q_\pm^2$. As a result, we directly handle the branch cut instead of utilizing the four-sheeted Riemann surface. Naturally, this approach leads to the discontinuity of the functions across their respective branch cuts, which significantly impacts the entire development of the IST.