ar X iv : m at h / 06 06 55 1 v 1 [ m at h . FA ] 2 2 Ju n 20 06 COMPLEX INTERPOLATION OF COMPACT OPERATORS

نویسندگان

  • MICHAEL CWIKEL
  • SVANTE JANSON
چکیده

If (A 0 , A 1) and (B 0 , B 1) are Banach couples and a linear operator T : A 0 + A 1 → B 0 + B 1 maps A 0 compactly into B 0 and maps A 1 boundedly into B 1 , does T necessarily also map [A 0 , A 1 ] θ compactly into [B 0 , B 1 ] θ for θ ∈ (0, 1)? After 42 years this question is still not answered, not even in the case where T : A 1 → B 1 is also compact. But affirmative answers are known for many special choices of (A 0 , A 1) and (B 0 , B 1). Furthermore it is known that it would suffice to resolve this question in the special case where (B 0 , B 1) is the special couple (ℓ ∞ (F L ∞), ℓ ∞ (F L ∞ 1)). Here F L ∞ is the space of all sequences {λn} n∈Z which are Fourier coefficients of essentially bounded functions, and F L ∞ 1 is the weighted space of all sequences {λn} n∈Z such that {e n λn} n∈Z ∈ F L ∞. We provide an affirmative answer to this question in the related but simpler case where (B 0 , B 1) is the special couple (F L ∞ , F L ∞ 1).

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تاریخ انتشار 2006