Fejér--Riesz factorization for positive noncommutative trigonometric polynomials

Igor Klep, Jacob Levenson, Scott McCullough

We prove a Fejér-Riesz type factorization for positive matrix-valued noncommutative trigonometric polynomials on $\mathcal{W}\times \mathfrak{Y}$, where $\mathcal{W}$ is either the…