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Earl Berkson
Rotation methods in operator ergodic theory view print
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Published: |
February 7, 2011 |
Keywords: |
spectral decomposition, trigonometrically well-bounded operator, higher variation, Fourier series |
Subject: |
Primary 26A45, 42A16, 47B40 |
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Abstract
Let E(⋅):R→B(X)
be the spectral decomposition of a trigonometrically
well-bounded operator U acting on the arbitrary Banach space X,
and suppose that the bounded function ϕ:T→ C
has the property that for each z∈T, the spectral integral
∫[0,2π]ϕ(eit) dEz(t)
exists, where Ez(⋅) denotes the spectral
decomposition of the (necessarily) trigonometrically well-bounded operator
(zU). We show this implies that for each z∈ T,
the spectral integral with respect to E(⋅) of the
rotated function ϕz(⋅) ≡ ϕ((⋅)z) exists. In particular, these considerations furnish
the preservation under rotation of spectral integration for the
Marcinkiewicz r-classes of multipliers Mr(T),
which are not themselves rotation-invariant. In the setting of an
arbitrary super-reflexive space, we pursue a different aspect of the impact
of rotations on the operator ergodic theory framework by applying the
rotation group to the spectral integration of functions of higher variation
so as to obtain strongly convergent Fourier series expansions for the
operator theory counterparts of such functions. This vector-valued Fourier
series convergence can be viewed as an extension of classical
Calderón-Coifman-Weiss transference without being tied to the need of the latter
for power-boundedness assumptions.
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Author information
Department of Mathematics; University of Illinois; 1409 W. Green Street; Urbana, IL 61801 USA
berkson@math.uiuc.edu
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