A note on uniqueness for linear evolution PDEs posed on the quarter-plane

Abstract: In this paper, we announce a rigorous approach to establishing uniqueness results, under certain conditions, for initial-boundary-value problems for a class of linear evolution partial differential equations (PDEs) formulated in a quarter-plane. We also effectively propose an algorithm for constructing non-uniqueness counter-examples which do not satisfy the said conditions. Our approach relies crucially on the rigorous analysis of regularity and asymptotic properties of integral representations derived formally via the celebrated Unified Transform Method for each such PDE. For uniqueness, this boundary behavior analysis allows for a careful implementation of an energy-estimate argument on the semi-unbounded domain. Our ideas are elucidated via application of the present technique to two concrete examples, namely the heat equation and the linear KdV equation with Dirichlet data on the positive quadrant, under a particular set of conditions at the domain boundary and at infinity. Importantly, this is facilitated by delicate refinement of previous results concerning the boundary behavior analysis of these two celebrated models. In addition, we announce a uniqueness theorem for the linearized BBM equation, whose proof, in a similar spirit, will appear in a forthcoming paper. Finally, we briefly demonstrate how the general case of oblique Robin data can be recast as a Dirichlet problem. To the best of our knowledge, such well-posedness results appear for the first time in either the classical or the weak sense. Extensions to other classes of equations are underway and will appear elsewhere.