Peak algebra in noncommuting variables

Abstract: The well-known descent-to-peak map $\Theta_{\mathrm{QSym}}$ for the Hopf algebra of quasisymmetric functions, $\mathrm{QSym}$, and the peak algebra $\Pi$ were originally defined by Stembridge in 1997. We define the labelled descent-to-peak map $\Theta_{\mathrm{NCQSym}}$ and extend the notion of the peak algebra to noncommuting variables. Moreover, we define Schur $Q$-functions in noncommuting variables having properties analogous to the classical Schur $Q$-functions.