$d$-plane transform: Unique and non-unique continuation

Abstract:

The $d$-plane transform maps functions to their integrals over $d$-planes in $\mathbb {R}^n$. We study the following question: if a function vanishes in a bounded open set, and its $d$-plane transform vanishes on all $d$-planes intersecting the same set, does the function vanish identically? For $d$ an even integer, we show by producing an explicit counterexample that neither the $d$-plane transform nor its normal operator has this property. On the other hand, an even stronger property holds when $d$ is odd, where the normal operator vanishing to infinite order at a point, along with the function vanishing on an open set containing that point, is sufficient to conclude that the function vanishes identically.