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Singular Degenerations of Lie Supergroups of Type $D(2,1;a)$
Kenji Ioharaa, Fabio Gavarinib a Univ Lyon, Université Claude Bernard Lyon 1, CNRS UMR 5208, Institut Camille Jordan, 43 Boulevard du 11 Novembre 1918, F 69622 Villeurbanne Cedex, France
b Dipartimento di Matematica, Università di Roma ''Tor Vergata'', Via della ricerca scientifica 1, I-00133 Roma, Italy
Abstract:
The complex Lie superalgebras $\mathfrak{g}$ of type $D(2,1;a)$ – also denoted by $\mathfrak{osp}(4,2;a) $ – are usually considered for “non-singular” values of the parameter $a$, for which they are simple. In this paper we introduce five suitable integral forms of $\mathfrak{g}$, that are well-defined at singular values too, giving rise to “singular specializations” that are no longer simple: this extends the family of simple objects of type $D(2,1;a)$ in five different ways. The resulting five families coincide for general values of $ a$, but are different at “singular” ones: here they provide non-simple Lie superalgebras, whose structure we describe explicitly. We also perform the parallel construction for complex Lie supergroups and describe their singular specializations (or “degenerations”) at singular values of $a$. Although one may work with a single complex parameter $a$, in order to stress the overall $\mathfrak{S}_3$-symmetry of the whole situation, we shall work (following Kaplansky) with a two-dimensional parameter $\sigma = (\sigma_1,\sigma_2,\sigma_3)$ ranging in the complex affine plane $\sigma_1 + \sigma_2 + \sigma_3 = 0$.
Keywords:
Lie superalgebras; Lie supergroups; singular degenerations; contractions.
Received: October 31, 2017; in final form December 11, 2018; Published online December 31, 2018
Citation:
Kenji Iohara, Fabio Gavarini, “Singular Degenerations of Lie Supergroups of Type $D(2,1;a)$”, SIGMA, 14 (2018), 137, 36 pp.
Linking options:
https://www.mathnet.ru/eng/sigma1436 https://www.mathnet.ru/eng/sigma/v14/p137
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Abstract page: | 111 | Full-text PDF : | 145 | References: | 15 |
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