The Truncated Moment Problem on Reducible Cubic Curves I: Parabolic and Circular Type Relations

In this article we study the bivariate truncated moment problem (TMP) of degree 2k on reducible cubic curves. First we show that every such TMP is equivalent after applying an affine linear transformation to one of 8 canonical forms of the curve. The case of the union of three parallel lines was solved in Zalar (Linear Algebra Appl 649:186–239, 2022. https://doi.org/10.1016/j.laa.2022.05.008), while the degree 6 cases in Yoo (Integral Equ Oper Theory 88:45–63, 2017). Second we characterize in terms of concrete numerical conditions the existence of the solution to the TMP on two of the remaining cases concretely, i.e., a union of a line and a circle \(y(ay+x^2+y^2)=0, a\in {\mathbb {R}}{\setminus } \{0\}\), and a union of a line and a parabola \(y(x-y^2)=0\). In both cases we also determine the number of atoms in a minimal representing measure.