Abstract
A general method for estimating the approximation numbers of composition operators on the Hardy space H 2, using finite-dimensional model subspaces, is studied and applied in the case when the symbol of the operator maps the unit disc to a domain whose boundary meets the unit circle at just one point. The exact rate of decay of the approximation numbers is identified when this map is sufficiently smooth at the point of tangency; it follows that a composition operator with any prescribed slow decay of its approximation numbers can be explicitly constructed. Similarly, an asymptotic expression for the approximation numbers is found when the mapping has a sharp cusp at the distinguished boundary point. Precise asymptotic estimates in the intermediate cases, including that of maps with a corner at the distinguished boundary point, are also established.
Similar content being viewed by others
References
J. R. Akeroyd, On Shapiro’s compactness criterion for composition operators, J. Math. Anal. Appl. 379 (2011), 1–7.
R. P. Boas, A general moment problem, Amer. J. Math. 63 (1941), 361–370.
B. Carl and I. Stephani, Entropy, Compactness and the Approximation of Operators, Cambridge University Press, Cambridge, 1990.
L. Carleson, An interpolation problem for bounded analytic functions, Amer. J. Math. 80 (1958), 921–930.
L. Carleson, Interpolations by bounded analytic functions and the corona problem, Ann. of Math. (2) 76 (1962), 547–559.
T. Carroll and C. C. Cowen, Compact composition operators not in the Schatten classes, J. Operator Theory 26 (1991), 109–120.
C. C. Cowen, Composition operators on Hilbert spaces of analytic functions: a status report, Operator Theory: Operator Algebras and Applications, Part 1, Amer. Math. Soc., Providence, RI, 1990.
J. B. Garnett, Bounded Analytic Functions, Springer, New York, 2007.
M. Jones, Compact composition operators not in the Schatten classes, Proc. Amer. Math. Soc. 134 (2006), 1947–1953.
P. Lefevre, D. Li, H. Queffélec, and L. Rodríguez-Piazza, Some examples of compact composition operators on H 2, J. Funct. Anal. 255 (2008), 3098–3124.
P. Lefevre, D. Li, H. Queffélec, and L. Rodríguez-Piazza, Some new properties of composition operators associated with lens maps, Israel J. Math. 195 (2013), 801–824.
D. Li, H. Queffélec, and L. Rodríguez-Piazza, On approximation numbers of composition operators, J. Approx. Theory 164 (2012), 431–459.
D. Li, H. Queffélec, and L. Rodríguez-Piazza, Estimates for approximation numbers of some classes of composition operators on the Hardy space, Ann. Acad. Sci. Fenn. Math. 38 (2013), 547–564.
D. H. Luecking and K. Zhu, Composition operators belonging to the Schatten ideals, Amer. J. Math. 114 (1992) 878–906.
B. D. MacCluer, Compact composition operators on Hp(BN), Michigan Math. J. 32 (1985), 237–248.
A. Pietsch, s-numbers of operators in Banach spaces, Studia Math. 51 (1974), 201–223.
H. Queffélec and K. Seip, Approximation numbers of composition operators on the H 2 space of Dirichlet series, J. Funct. Anal.; to appear, arXiv: 1302.4116v2[math.FA].
A. P. Schuster and K. Seip, A Carleson-type condition for interpolation in Bergman spaces, J. Reine Angew. Math. 497 (1998), 223–233.
J. H. Shapiro, The essential norm of a composition operator, Ann. of Math. (2) 125 (1987), 375–404.
J. H. Shapiro, Composition Operators and Classical Function Theory, Springer-Verlag, New York, 1993.
H. S. Shapiro and A. L. Shields, On some interpolation problems for analytic functions, Amer. J. Math. 83 (1961), 513–532.
Y. Zhu, Geometric properties of composition operators belonging to Schatten classes, Int. J. Math. Sci. 26 (2001), 239–248.
Author information
Authors and Affiliations
Corresponding author
Additional information
This paper was written while the authors participated in the research program Operator Related Function Theory and Time-Frequency Analysis at the Centre for Advanced Study at the Norwegian Academy of Science and Letters in Oslo during 2012–2013.
The second author is supported by the Research Council of Norway grant 227768.
Rights and permissions
About this article
Cite this article
Queffélec, H., Seip, K. Decay rates for approximation numbers of composition operators. JAMA 125, 371–399 (2015). https://doi.org/10.1007/s11854-015-0012-6
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11854-015-0012-6