English

Bounded Point Evaluations For Certain Polynomial And Rational Modules

Functional Analysis 2019-03-21 v1

Abstract

Let KK be a compact subset of the complex plane C.\mathbb C. Let P(K)P(K) and R(K)R(K) be the closures in C(K)C(K) of analytic polynomials and rational functions with poles off K,K, respectively. Let A(K)C(K)A(K) \subset C(K) be the algebra of functions that are analytic in the interior of KK. For 1t<,1\le t <\infty, let Pt(1,ϕ1,...,ϕN,K)P^t(1, \phi_1,...,\phi_N,K) be the closure of P(K)+P(K)ϕ1+...+P(K)ϕNP(K)+P(K)\phi_1+...+P(K)\phi_N in Lt(dAK),L^t(dA|_K), where dAKdA|_K is the area measure restricted to KK and ϕ1,...,ϕNLt(dAK).\phi_1,...,\phi_N\in L^t(dA|_K). Let HP(ϕ1,...,ϕN,K)HP(\phi_1,...,\phi_N,K) be the closure of P(K)ϕ1+...+P(K)ϕN+R(K)P(K)\phi_1+...+P(K)\phi_N +R(K) in C(K),C(K), where ϕ1,...,ϕNC(K).\phi_1,...,\phi_N\in C(K). In this paper, we prove if R(K)C(K),R(K)\ne C(K), then there exists an analytic bounded point evaluation for both Pt(1,ϕ1,...,ϕN,K)P^t(1, \phi_1,...,\phi_N,K) and HP(ϕ1,...,ϕN,K)HP(\phi_1,...,\phi_N,K) for certain smooth functions ϕ1,...,ϕN,\phi_1,...,\phi_N, in particular, for zˉ,zˉ2,...,zˉN.\bar z,\bar z^2,...,\bar z^N. We show that A(K)HP(zˉ,zˉ2,...,zˉN,K)A(K)\subset HP(\bar z,\bar z^2,...,\bar z^N,K) if and only if R(K)=A(K).R(K) = A(K). In particular, C(K)HP(zˉ,zˉ2,...,zˉN,K)C(K) \ne HP(\bar z,\bar z^2,...,\bar z^N,K) unless R(K)=C(K).R(K) = C(K). We also give an example of KK showing the results are not valid if we replace zˉn\bar z^n by certain ϕn,\phi_n, that is, there exist KK and a function ϕA(K)\phi\in A(K) such that R(K)A(K),R(K) \ne A(K), but A(K)=HP(ϕ,K).A(K) = HP (\phi ,K).

Keywords

Cite

@article{arxiv.1711.03715,
  title  = {Bounded Point Evaluations For Certain Polynomial And Rational Modules},
  author = {Liming Yang},
  journal= {arXiv preprint arXiv:1711.03715},
  year   = {2019}
}
R2 v1 2026-06-22T22:41:49.701Z