Let
be a
-adic field and
a quadratic
extension of
.
Using Tadić’s classification of the unitary dual of
, we
give the list of irreducible unitary representations of this group distinguished by
in terms
of distinguished discrete series. It is known that a generalised Steinberg representation
is distinguished if and only if the cuspidal representation
is
-distinguished for
, the character of
with kernel consisting
of the norms of
.
This actually gives a classification of distinguished unitary representations in terms of
distinguished cuspidal representations.