Abstract
For two complex Banach spaces X and Y, \(\mathcal{A}_\infty \) (B X; Y) will denote the space of bounded and continuous functions from B X to Y that are holomorphic on the open unit ball. The numerical radius of an element h in \(\mathcal{A}_\infty \) (B X; X) is the supremum of the set
. We prove that every complex Banach space X with the Radon-Nikodým property satisfies that the subset of numerical radius attaining functions in \(\mathcal{A}_\infty \) (B X; X) is dense in \(\mathcal{A}_\infty \) (B X; X). We also show the denseness of the numerical radius attaining elements of \(\mathcal{A}_u (B_{c_0 } ; c_0 )\) in the whole space, where \(\mathcal{A}_u (B_{c_0 } ; c_0 )\) is the subset of functions in \(\mathcal{A}_\infty (B_{c_0 } ; c_0 )\) which are uniformly continuous on the unit ball. For C(K) we prove a denseness result for the subset of the functions in \(\mathcal{A}_\infty \) (B C(K); C(K)) which are weakly uniformly continuous on the closed unit ball. For a certain sequence space X, there is a 2-homogenous polynomial P from X to X such that for every R > e, P cannot be approximated by bounded and numerical radius attaining holomorphic functions defined on RB X . If Y satisfies some isometric conditions and X is such that the subset of norm attaining functions of \(\mathcal{A}_\infty \) (B X; ℂ) is dense in \(\mathcal{A}_\infty \) (B X; ℂ), then the subset of norm attaining functions in \(\mathcal{A}_\infty \) (B X; Y) is dense in the whole space.
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References
M. D. Acosta, Boundaries for spaces of holomorphic functions on C(K), Publications of the Research Institute for Mathematical Sciences 42 (2006), 27–44.
M. D. Acosta, F. Aguirre and R. Payá, A space by W. Gowers and new results on norm and numerical radius attaining operators, Acta Univ. Carolin. Math. Phys 33 (1992), 5–14.
M. D. Acosta, J. Alaminos, D. García and M. Maestre, On holomorphic functions attaining their norms, Journal of Mathematical Analysis and Applications 297 (2004), 625–644.
M. D. Acosta and R. Payá, Numerical radius attaining operators and the Radon-Nikodym property, The Bulletin of the London Mathematical Society 25 (1993), 67–73.
Y. S. Choi, D. García, S. G. Kim and M. Maestre, Norm or numerical radius attaining polynomials on C(K), Journal of Mathematical Analysis and Applications 295 (2004), 80–96.
Y. S. Choi and S. G. Kim, Norm or numerical radius attaining multilinear mappings and polynomials, Journal of the London Mathematical Society 54 (1996), 135–147.
P. Harmand, D. Werner and W. Werner, M-ideals in Banach Spaces and Banach Algebras, Lecture Notes in Mathematics 1547, Springer-Verlag, Berlin, 1993.
L. Harris, The numerical range of holomorphic functions in Banach spaces, American Jouranl of Mathematics 93 (1971), 1005–1119.
J. Johnson and J. Wolfe, Norm attaining operators, Studia Mathematica 65 (1979), 7–19.
J. Lindenstrauss, On operators which attain their norms, Israel Journal of Mathematics 1 (1963), 139–148.
A. Moltó, V. Montesinos and S. Troyanski, On quasi-denting points, denting faces and the geometry of the unit ball of d(w, 1), Archiv der Mathematik 63 (1994), 45–55.
J. Partington, Norm attaining operators, Israel Journal of Mathematics 43 (1982), 273–276.
C. Stegall, Optimization and differentiation in Banach Spaces, Linear Algebra and its Applications 84 (1986), 191–211.
D. Werner, New classes of Banach spaces which are M-ideals in their biduals, Mathematical Proceedings of the Cambridge Philosophical Society 111 (1992), 337–354.
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The first author was supported in part by D.G.E.S. Project BFM2003-01681.
The second author’s work was performed during a visit to the Departamento de Análisis Matem’atico of Universidad de Granada, with a grant supported by the Korea Research Foundation under grant (KRF-2002-070-C00006).
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Acosta, M.D., Kim, S.G. Denseness of holomorphic functions attaining their numerical radii. Isr. J. Math. 161, 373–386 (2007). https://doi.org/10.1007/s11856-007-0083-x
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DOI: https://doi.org/10.1007/s11856-007-0083-x