Back to Degree 2, Back to the start
L-functions of degree 2 and level 2 correspond to newforms on
.
They can be expressed as linear combinations of products of the basic
Eisenstein series which we now introduce.
First of all,
is the Eisenstein series of weight 2. It corresponds to the Dirichlet series
which, after normalization, satisfies a functional
equation of type
but is not in
the Selberg class. For even weights greater than 2 we can construct modular
forms from the Eisenstein series on the full modular group. Thus, for k an
even integer, we let
and
These are modular forms of weight k for
which have
multiplicative coefficients and which are eigenforms of the matrix
with eigenvalue
+1 or -1 according to the superscript on the E.
corresponds to the Dirichlet series
which, after normalization, has functional equation of type
and
corresponds to the Dirichlet series
which, after normalization, has functional equation of type
Thus,