English

Contractivity, Complete Contractivity and Curvature inequalities

Functional Analysis 2014-08-12 v1

Abstract

Let A\|\cdot\|_{\mathbf A} be a norm on Cm\mathbb C^m given by the formula (z1,,zm)A=z1A1++zmAmop\|(z_1,\ldots,z_m)\|_{\mathbf A}=\|z_1A_1+\cdots+z_mA_m\|_{\rm op} for some choice of an mm-tuple of n×nn\times n linearly independent matrices A=(A1,,Am).\mathbf A=(A_1, \ldots, A_m). Let ΩACm\Omega_\mathbf A\subset \mathbb C^m be the unit ball with respect to the norm A.\|\cdot\|_{\mathbf A}. %For a holomorphic function ff on ΩA,\Omega_\mathbf A, let %\rho_{V}(f):=\left ( %\begin{smallmatrix} %f(w)I_p& \sum_{i=1}^{m} \partial_if(w)V_{i} \\ %0 & f(w)I_q %\end{smallmatrix}\right ), where V1,,VmV_1, \ldots, V_m are p×qp\times q %matrices. Given p×qp\times q matrices V1,,VmV_1, \ldots, V_m and a function fO(ΩA),f \in \mathcal O(\Omega_\mathbf A), the algebra of function holomorphic on an open set UU containing the closed unit ball ΩˉA\bar{\Omega}_\mathbf A define ρV(f):=(f(w)Ipi=1mif(w)Vi0f(w)Iq),\rho_{V}(f):=\left ( \begin{smallmatrix} f(w)I_p& \sum_{i=1}^{m} \partial_if(w)V_{i} \\ 0 & f(w)I_q \end{smallmatrix}\right ), wΩA.w\in \Omega_\mathbf A. Clearly, ρV\rho_{V} defines an algebra homomorphism. We study contractivity (resp. complete contractivity) of such homomorphisms. The characterization of those balls in C2\mathbb C^2 for which contractive linear maps are always completely contractive remained open. We answer this question for balls of the form ΩA\Omega_\mathbf A in C2.\mathbb C^2. The class of homomorphisms of the form ρV\rho_V arise from localization of operators in the Cowen-Douglas class of Ω.\Omega. The (complete) contractivity of a homomorphism in this class naturally produces inequalities for the curvature of the corresponding Cowen-Douglas bundle. This connection and some of its very interesting consequences are discussed.

Keywords

Cite

@article{arxiv.1408.2389,
  title  = {Contractivity, Complete Contractivity and Curvature inequalities},
  author = {Avijit Pal},
  journal= {arXiv preprint arXiv:1408.2389},
  year   = {2014}
}

Comments

This thesis was submitted at the Indian Institute of Science, Bangalore

R2 v1 2026-06-22T05:25:04.316Z