Nonlinear holomorphic supersymmetry, Dolan-Grady relations and Onsager algebra

Recently, it was noticed by us that the nonlinear holomorphic supersymmetry of order $n\in\N, n>1$, ($n$-HSUSY) has an algebraic origin. We show that the Onsager algebra underlies $n$-HSUSY and investigate the structure of the former in the context of the latter. A new infinite set of mutually commuting charges is found which, unlike those from the Dolan-Grady set, include the terms quadratic in the Onsager algebra generators. This allows us to find the general form of the superalgebra of $n$-HSUSY and fix it explicitly for the cases of $n=2,3,4,5,6$. The similar results are obtained for a new, contracted form of the Onsager algebra generated via the contracted Dolan-Grady relations. As an application, the algebraic structure of the known 1D and 2D systems with $n$-HSUSY is clarified and a generalization of the construction to the case of nonlinear pseudo-supersymmetry is proposed. Such a generalization is discussed in application to some integrable spin models and with its help we obtain a family of quasi-exactly solvable systems appearing in the $PT$-symmetric quantum mechanics.Comment: 18 pages, refs updated; to appear in Nucl. Phys.

Note on antisymmetric spin-tensors

It was known for a long time that in d = 4 dimensions it is impossible to construct the Lagrangian for antisymmetric second rank spin-tensor that will be invariant under the gauge transformations with unconstrained spin-vector parameter. But recently a paper arXiv:0902.1471 appeared where gauge invariant Lagrangians for antisymmetric spin-tensors of arbitrary rank n in d > 2n were constructed using powerful BRST approach. To clarify apparent contradiction, in this note we carry a direct independent analysis of the most general first order Lagrangian for the massless antisymmetric spin-tensor of second rank. Our analysis shows that gauge invariant Lagrangian does exist but in d > 4 dimensions only, while in d = 4 this Lagrangian becomes identically zero. As a byproduct, we obtain a very simple and convenient form of this massless Lagrangian that makes deformation to AdS space and/or massive case a simple task as we explicitly show here. Moreover, this simple form admits natural and straightforward generalization on the case of massive antisymmetric spin-tensors of rank n for d > 2n.Comment: 7 pages, no figure

Nonlinear Holomorphic Supersymmetry on Riemann Surfaces

We investigate the nonlinear holomorphic supersymmetry for quantum-mechanical systems on Riemann surfaces subjected to an external magnetic field. The realization is shown to be possible only for Riemann surfaces with constant curvature metrics. The cases of the sphere and Lobachevski plane are elaborated in detail. The partial algebraization of the spectrum of the corresponding Hamiltonians is proved by the reduction to one-dimensional quasi-exactly solvable sl(2,R) families. It is found that these families possess the "duality" transformations, which form a discrete group of symmetries of the corresponding 1D potentials and partially relate the spectra of different 2D systems. The algebraic structure of the systems on the sphere and hyperbolic plane is explored in the context of the Onsager algebra associated with the nonlinear holomorphic supersymmetry. Inspired by this analysis, a general algebraic method for obtaining the covariant form of integrals of motion of the quantum systems in external fields is proposed.Comment: 24 pages, new section and refs added; to appear in Nucl. Phys.

Gravitational and higher-derivative interactions of massive spin 5/2 field in (A)dS space

Using on-shell gauge invariant formulation of relativistic dynamics we study interaction vertices for a massive spin 5/2 Dirac field propagating in (A)dS space of dimension greater than or equal to four. Gravitational interaction vertex for the massive spin 5/2 field and all cubic vertices for the massive spin 5/2 field and massless spin 2 field with two and three derivatives are obtained. In dimension greater that four, we demonstrate that the gravitational vertex of the massive spin 5/2 field involves, in addition to the standard minimal gravitational vertex, contributions with two and three derivatives. We find that for the massive spin 5/2 and massless spin 2 fields one can build two higher-derivative vertices with two and three derivatives. Limits of massless and partial massless spin 5/2 fields in (A)dS space and limits of massive and massless spin 5/2 fields in flat space are discussed.Comment: 51 pages, LaTeX-2e, v3: Section 1 is divided into Sections 1-6. Discussion of gravitational and higher-derivative vertices added to Sections 2-6. Tables I, II and Appendices B,C,D,E,F added. Typos correcte