The Borichev-Tomilov theorem characterizes polynomial decay of a bounded strongly continuous semigroup on a Hilbert space. Such
decay is a form of semigroup stability. Let
have infinitesimal generator
, suppose that the imaginary
axis is contained in the resolvent set of
,
and let
.
Then
Here
is the identity operator, and
is the resolvent
operator at
. Thus a quantitative frequency-domain estimate gives the
corresponding optimal polynomial rate in the time domain.