© 1999 by London Mathematical Society
© The London Mathematical Society
Sandwiching C0-Semigroups
Department of Mathematics, Delft University of Technology PO Box 5031, 2600 GA Delft, Netherlands J.vanNeerven{at}twi.tudelft.nl
Received 11 September 1997. Revision received 8 April 1998.
Let T = {T(t)}t
0 be a C0-semigroup on a Banach space X. The following results are proved.
(i) If X is separable, there exist separable Hilbert spaces X0 and X1, continuous dense embeddings j0:X0
X and j1:X
X1, and C0-semigroups T0 and T1 on X0 and X1 respectively, such that j0
T0(t) = T(t)
j0 and T1(t)
j1 = j1
T(t) for all t
0.
(ii) If T is
-reflexive, there exist reflexive Banach spaces X0 and X1 , continuous dense embeddings j:D(A2)
X0, j0:X0
X, j1:X
X1, and C0-semigroups T0 and T1 on X0 and X1 respectively, such that T0(t)
j = j
T(t), j0
T0(t) = T(t)
j0 and T(t)
j1 = j1
T(t) for all t
0, and such that
(A0) =
(A) =
(A1), where Ak is the generator of Tk, k = 0, Ø, 1.