On $Γ_n$-contractions and their Conditional Dilations (1704.04508v2)

Abstract: We prove some estimates for elementary symmetric polynomials on $\mathbb D^n.$ We show that these estimates are sharp which allow us to study the properties of closed symmetrized polydisc $\Gamma_n.$ Furthermore, we show the existence and uniqueness of solutions to the operator equations $$S_i-S_{n-i}^*S_n=D_{S_n}X_iD_{S_n}{\rm{and}}S_{n-i}-S_{i}^*S_n=D_{S_n}X_{n-i}D_{S_n},$$ where $X_i,X_{n-i}\in \mathcal B(\mathcal D_{S_n}), ~{\rm{for ~all~}} i=1,\ldots,(n-1),$ with numerical radius not greater than $1,$ for a $\Gamma_n$-contraction $(S_1,\ldots, S_n).$ We construct a conditional dilation of various classes of $\Gamma_n$-contractions. Various properties of a $\Gamma_n$-contraction and its explicit dilation allow us to construct a concrete functional model for a $\Gamma_n$-contraction. We describe the structure and additional characterization of $\Gamma_n$-unitaries and $\Gamma_n$-isometries in detail.