Roots of Toeplitz operators on the Bergman space

Abstract

One of the major questions in the theory of Toeplitz operators on the Bergman space over the unit disk $\mathbb D$ in the complex plane $\mathbb C$ is a complete description of the commutant of a given Toeplitz operator, that is the set of all Toeplitz operators that commute with it. In \cite{l}, the first author obtained a complete description of the commutant of Toeplitz operator $T$ with any quasihomogeneous symbol $\phi(r)e^{ip\theta}, p>0$ in case it has a Toeplitz p-th root $S$ with symbol $\psi(r)e^{i\theta}$, namely, commutant of $T$ is the closure of the linear space generated by powers $S^n$ which are Toeplitz. But the existence of p-th root was known until now only when $\phi(r)=r^m,m \geq 0$. In this paper we will show the existence of p-th roots for a much larger class of symbols, for example, it includes such symbols for which $$\phi(r)=\sum_{i=1}^kr^{a_i}(\ln r)^{b_i},0\leq a_i, b_i for all 1\leq i\leq k .$$