A Letter Highlighting Matrix Mapping in Minimal 4D, ${\mathbf {\cal N}}$ = 1 On-Shell Supermultiplet Representations

On the basis of comparing eigenvalues of an operator ${\hat {\mathbf{\cal C}}}{}^{({\cal R})}$, that proved useful in distinguishing how off-shell 4D, $\cal N$ = 1 supermultiplets become off-shell 4D, $\cal N$ = 2 supermultiplets, the double tensor supermultiplet is shown to be radically different for other known multiplets. This suggests difficulties, if not impossibilities, to embed it into an off-shell structure.