Summary: We investigate the notion of super-unitarity from a functional analytic point of view. For this purpose we consider examples of explicit realizations of a certain type of irreducible representations of low rank orthosymplectic Lie superalgebras which are super-unitary by construction. These are the so-called superholomorphic discrete series representations of \(\text{osp}(1/2,\mathbb{R})\) and \(\text{osp}(2/2,\mathbb{R})\) which we recently constructed using a \(\mathbb{Z}_2\)-graded extension of the orbit method [A. M. El Gradechi, Lett. Math. Phys. 35, 13-26 (1995; Zbl 0841.58030); A. M. El Gradechi and L. M. Nieto, Commun. Math. Phys. 175, 521-563 (1996; Zbl 0840.58010)]. It turns out here that super-unitarity of these representations is a consequence of the self-adjointness of two pairs of anticommuting operators which act in the Hilbert sum of two Hilbert spaces, each of which carries a holomorphic discrete series representation of su(1,1) such that the difference of the respective lowest weights is \(\frac 12\).
At an intermediate stage, we show that the generators of the considered orthosymplectic Lie superalgebras can be realized either as matrix-valued first-order differential operators or as first order differential superoperators. Even though the former realization is less convenient than the latter from the computational point of view, it has the advantage of avoiding the use of anticommuting Grassmann variables, and it is moreover important for our analysis of super-unitarity. The latter emphasizes the fundamental role played by the atypical (or degenerate) superholomorphic discrete series representations of osp(2/2,\(\mathbb{R}\)) for the super-unitarity of the other representations considered in this work, and it shows that the anticommuting (unbounded) self-adjoint operators mentioned above anticommute in a proper sense, thus connecting our work with the analysis of supersymmetric quantum mechanics.