Extremely non-complex Banach spaces

Miguel Martín; Javier Merí

Open Mathematics (2011)

  • Volume: 9, Issue: 4, page 797-802
  • ISSN: 2391-5455

Abstract

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A Banach space X is said to be an extremely non-complex space if the norm equality ∥Id +T 2∥ = 1+∥T 2∥ holds for every bounded linear operator T on X. We show that every extremely non-complex Banach space has positive numerical index, it does not have an unconditional basis and that the infimum of diameters of the slices of its unit ball is positive.

How to cite

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Miguel Martín, and Javier Merí. "Extremely non-complex Banach spaces." Open Mathematics 9.4 (2011): 797-802. <http://eudml.org/doc/269605>.

@article{MiguelMartín2011,
abstract = {A Banach space X is said to be an extremely non-complex space if the norm equality ∥Id +T 2∥ = 1+∥T 2∥ holds for every bounded linear operator T on X. We show that every extremely non-complex Banach space has positive numerical index, it does not have an unconditional basis and that the infimum of diameters of the slices of its unit ball is positive.},
author = {Miguel Martín, Javier Merí},
journal = {Open Mathematics},
keywords = {Banach space; Complex structure; Daugavet equation; Extremely non-complex; Numerical index; Diameter of slices; complex structure; extremely non-complex Banach space; numerical index; diameter of slices},
language = {eng},
number = {4},
pages = {797-802},
title = {Extremely non-complex Banach spaces},
url = {http://eudml.org/doc/269605},
volume = {9},
year = {2011},
}

TY - JOUR
AU - Miguel Martín
AU - Javier Merí
TI - Extremely non-complex Banach spaces
JO - Open Mathematics
PY - 2011
VL - 9
IS - 4
SP - 797
EP - 802
AB - A Banach space X is said to be an extremely non-complex space if the norm equality ∥Id +T 2∥ = 1+∥T 2∥ holds for every bounded linear operator T on X. We show that every extremely non-complex Banach space has positive numerical index, it does not have an unconditional basis and that the infimum of diameters of the slices of its unit ball is positive.
LA - eng
KW - Banach space; Complex structure; Daugavet equation; Extremely non-complex; Numerical index; Diameter of slices; complex structure; extremely non-complex Banach space; numerical index; diameter of slices
UR - http://eudml.org/doc/269605
ER -

References

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  1. [1] Duncan J., McGregor C.M., Pryce J.D., White A.J., The numerical index of a normed space, J. Lond. Math. Soc., 1970, 2, 481–488 Zbl0197.10402
  2. [2] Kadets V.M., Some remarks concerning the Daugavet equation, Quaest. Math., 1996, 19(1–2), 225–235 http://dx.doi.org/10.1080/16073606.1996.9631836 
  3. [3] Kadets V., Katkova O., Martín M., Vishnyakova A., Convexity around the unit of a Banach algebra, Serdica Math. J., 2008, 34(3), 619–628 Zbl1224.46025
  4. [4] Kadets V., Martín M., Merí J., Norm equalities for operators, Indiana Univ. Math. J., 2007, 56(5), 2385–2411 http://dx.doi.org/10.1512/iumj.2007.56.3046 Zbl1132.46006
  5. [5] Kadets V.M., Shvidkoy R.V., Sirotkin G.G., Werner D., Banach spaces with the Daugavet property, Trans. Amer. Math. Soc., 2000, 352(2), 855–873 http://dx.doi.org/10.1090/S0002-9947-99-02377-6 Zbl0938.46016
  6. [6] Koszmider P., Banach spaces of continuous functions with few operators, Math. Ann., 2004, 330(1), 151–183 http://dx.doi.org/10.1007/s00208-004-0544-z Zbl1064.46009
  7. [7] Koszmider P., Martín M., Merí J., Extremely non-complex C(K) spaces, J. Math. Anal. Appl., 2009, 350(2), 601–615 http://dx.doi.org/10.1016/j.jmaa.2008.04.021 Zbl1162.46016
  8. [8] Koszmider P., Martín M., Merí J., Isometries on extremely non-complex C(K) spaces, J. Inst. Math. Jussieu, 2011, 10(2), 325–348 http://dx.doi.org/10.1017/S1474748010000204 Zbl1221.46012
  9. [9] Martín M., Oikhberg T., An alternative Daugavet property, J. Math. Anal. Appl., 2004, 294(1), 158–180 http://dx.doi.org/10.1016/j.jmaa.2004.02.006 Zbl1054.46010
  10. [10] Megginson R.E., An Introduction to Banach Space Theory, Grad. Texts in Math., 183, Springer, New York, 1998 Zbl0910.46008
  11. [11] Oikhberg T., Some properties related to the Daugavet property, In: Banach Spaces and their Applications in Analysis, Walter de Gruyter, Berlin, 2007, 399–401 Zbl1140.46305

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