You need to know: Set of integers, greatest common divisor (gcd) of 2 integers, set
of complex numbers,
notation.
Background: Function is called a Dirichlet character modulo integer
if (i)
for all n, (ii) if
then
; if
then
, and (iii)
for all integers m and n. An example is character
such that
whenever
and
otherwise. This character is called principal and all other characters – nonprincipal. The order of a Dirichlet character
is the least positive integer m such that
for all n. The character
is called primitive if there is no integer
such that
whenever
and
is a multiple of d. For any nonprincipal character
let
.
The Theorem: On 2nd March 2005, Andrew Granville and Kannan Soundararajan submitted to the Jornal of the AMS a paper in which they proved that that if is a primitive character modulo q of odd order g, then
where
, and
is a constant depending only on g.
Short context: In 1918, Pólya and Vinogradov independently proved that for any nonprincipal Dirichlet character
. This is known as the Pólya–Vinogradov inequality, has numerous applications, but it is an open question whether a better bound for
in terms of q is possible. The Theorem provides an improved bound for characters of odd, bounded order.
Links: Free arxiv version of the original paper is here, journal version is here.
One thought on “Pólya-Vinogradov bound is not tight for characters of odd, bounded order”