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Best constants for some operators associated with the Fourier and Hilbert transforms

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Hollenbeck B., Kalton N., Verbitsky I.

Studia Mathematica

2003

tom 157

nr 3

237-278

We determine the norm in $L^{p}(ℝ₊)$, 1 < p < ∞, of the operator $I - ℱ_{s}ℱ_{c}$, where $ℱ_{c}$ and $ℱ_{s}$ are respectively the cosine and sine Fourier transforms on the positive real axis, and I is the identity operator. This solves a problem posed in 1984 by M. S. Birman [Bir] which originated in scattering theory for unbounded obstacles in the plane. We also obtain the $L^{p}$-norms of the operators aI + bH, where H is the Hilbert transform (conjugate function operator) on the circle or real line, for arbitrary real a,b. Best constants in other related inequalities are found. In a more general framework, we present an alternative proof of the important theorem of Cole relating best constant inequalities involving the Hilbert transform and the existence of subharmonic minorants, which extends to several variables and plurisubharmonic minorants.

Ograniczanie wyników

1 Studia Mathematica

1 Hollenbeck B.

1 Kalton N.

1 Verbitsky I.

1 2003

Wyniki wyszukiwania

Best constants for some operators associated with the Fourier and Hilbert transforms