A Note on the Hurwitz Action on Reflection Factorizations of Coxeter Elements in Complex Reflection Groups

We show that the Hurwitz action is "as transitive as possible" on reflection factorizations of Coxeter elements in the well-generated complex reflection groups $G(d,1,n)$ (the group of $d$-colored permutations) and $G(d,d,n)$.

Some Identities Involving Second Kind Stirling Numbers of Types $B$ and $D$

Using Reiner's definition of Stirling numbers of the second kind in types $B$ and $D$, we generalize two well-known identities concerning the classical Stirling numbers of the second kind. The first identity relates them with Eulerian numbers and the second identity interprets them as entries in a transition matrix between the elements of two standard bases of the polynomial ring $\mathbb{R}[x]$. Finally, we generalize these identities to the group of colored permutations $G_{m,n}$.

$\lambda$-Euler's Difference Table for Colored Permutations

Motivated by the $\lambda$-Euler's difference table of Eriksen et al. and colored Euler's difference table of Faliharimalala and Zeng, we study the $\lambda$-analogue of colored Euler's difference table and generalize their results. We generalize the number of permutations with $k$-excedances studied by Liese and Remmel in colored permutations. We also extend Wang et al.'s recent results about $r$-derangements by relating with the sequences arising from the difference table.

Flag Statistics from the Ehrhart $h^∗$-Polynomial of Multi-Hypersimplices

It is known that the normalized volume of standard hypersimplices (defined as some slices of the unit hypercube) are the Eulerian numbers. More generally, a recent conjecture of Stanley relates the Ehrhart series of hypersimplices with descents and excedences in permutations. This conjecture was proved by Nan Li, who also gave a generalization to colored permutations. In this article, we give another generalization to colored permutations, using the flag statistics introduced by Foata and Han. We obtain in particular a new proof of Stanley’s conjecture, and some combinatorial identities relating pairs of Eulerian statistics on colored permutations.

Recursions for the flag-excedance number in colored permutations groups

The excedance number for Sn is known to have an Eulerian distribution. Nevertheless, the classical proof uses descents rather than excedances. We present a direct proof based on a recursion which uses only excedances and extend it to the flag-excedance parameter defined on the group of colored permutations Gr,n = ℤr ≀ Sn. We have also computed the distribution of a variant of the flag-excedance number, and show that its enumeration uses the Stirling number of the second kind. Moreover, we show that the generating function of the flag-excedance number defined on ℤr ≀ Sn is symmetric, and its variant is log-concave on ℤr ≀ Sn..

On the Group of Alternating Colored Permutations

The group of alternating colored permutations is the natural analogue of the classical alternating group, inside the wreath product $\mathbb{Z}_r \wr S_n$. We present a 'Coxeter-like' presentation for this group and compute the length function with respect to that presentation. Then, we present this group as a covering of $\mathbb{Z}_{\frac{r}{2}} \wr S_n$ and use this point of view to give another expression for the length function. We also use this covering to lift several known parameters of $\mathbb{Z}_{\frac{r}{2}} \wr S_n$ to the group of alternating colored permutations.