arXiv subjects
Publications and source records attributed to Shuichi Harako.
We construct a new presentation of the twisted Yangian of type $D$ with a finite number of generators. By using this presentation, we propose a new definition of the twisted affine Yangian of type $D$.
An almost commutative algebra, or a $ρ$-commutative algebra, is an algebra which is graded by an abelian group and whose commutativity is controlled by a function called a commutation factor. The same way as a formulation of a supermanifold as a ringed space, we introduce concepts of the $ρ$-commutative versions of manifolds, Q-manifolds, Berezin volume forms, and the modular classes. They are generalizations of the ones in supergeometry. We give examples including a $ρ$-commutative version of the Schouten bracket and a noncommutative torus.
The symplectic derivation Lie algebras defined by Kontsevich are related to various geometric objects including moduli spaces of graphs and of Riemann surfaces, graph homologies, Hamiltonian vector fields, etc. Each of them and its Chevalley-Eilenberg chain complex have a $\mathbb{Z}_{\geq 0}$-grading called weight. We consider one of them $\mathfrak{c}_g$, called the "commutative case", and its positive weight part $\mathfrak{c}_g^{+} \subset \mathfrak{c}_g$. The symplectic invariant homology of $\mathfrak{c}_g^{+}$ is closely related to the commutative graph homology, hence there are some computational results from the viewpoint of graph homology theory. However, the entire homology group $H_\bullet (\mathfrak{c}_g^{+})$ is not known well. We determined $H_2 (\mathfrak{c}_g^{+})$ by using classical representation theory of $\mathrm{Sp}(2g; \mathbb{Q})$ and the decomposition by weight.