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MAXIMAL SEMIGROUP SYMMETRY AND DISCRETE RIESZ TRANSFORMS
- Part of
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- Journal:
- Journal of the Australian Mathematical Society / Volume 100 / Issue 2 / April 2016
- Published online by Cambridge University Press:
- 14 December 2015, pp. 216-240
- Print publication:
- April 2016
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- Article
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- You have access
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We raise a question of whether the Riesz transform on
$\mathbb{T}^{n}$ or 
$\mathbb{Z}^{n}$ is characterized by the ‘maximal semigroup symmetry’ that the transform satisfies. We prove that this is the case if and only if the dimension is one, two or a multiple of four. This generalizes a theorem of Edwards and Gaudry for the Hilbert transform on 
$\mathbb{T}$ and 
$\mathbb{Z}$ in the one-dimensional case, and extends a theorem of Stein for the Riesz transform on 
$\mathbb{R}^{n}$. Unlike the 
$\mathbb{R}^{n}$ case, we show that there exist infinitely many linearly independent multiplier operators that enjoy the same maximal semigroup symmetry as the Riesz transforms on 
$\mathbb{T}^{n}$ and 
$\mathbb{Z}^{n}$ if the dimension 
$n$ is greater than or equal to three and is not a multiple of four.
