We study Hochschild (co)homology groups of the Dunkl operator quantization of
$\Z_2$-singularity constructed by Halbout and Tang. Further, we study traces on
this algebra and prove a local algebraic index formula.
We introduce a Hopf algebroid associated to a proper Lie group action on a
smooth manifold. We prove that the cyclic cohomology of this Hopf algebroid is
equal to the de Rham cohomology of invariant differential forms. When the
action is cocompact, we develop a generalized Hodge theory for the de Rham
cohomology of invariant differential forms. We prove that every cyclic
cohomology class of the Hopf algebroid is represented by a generalized harmonic
form. This implies that the space of cyclic cohomology of the Hopf algebroid is
finite dimensional.
This is a survey about recent progress in Rankin-Cohen deformations. We
explain a connection between Rankin-Cohen brackets and higher order Hankel
forms.
Let $(X,\omega)$ be a symplectic orbifold which is locally like the quotient
of a $\mathbb{Z}_2$ action on $\reals^n$. Let $A^{((\hbar))}_X$ be a
deformation quantization of $X$ constructed via the standard Fedosov method
with characteristic class being $\omega$. In this paper, we construct a
universal deformation of the algebra $A^{((\hbar))}_X$ parametrized by
codimension 2 components of the associated inertia orbifold $\widetilde{X}$.
This partially confirms a conjecture of Dolgushev and Etingof in the case of
$\mathbb{Z}_2$ orbifolds.