Chowla–Mordell theorem

In mathematics, the Chowla–Mordell theorem is a result in number theory determining cases where a Gauss sum is the square root of a prime number, multiplied by a root of unity. It was proved and published independently by Sarvadaman Chowla and Louis Mordell, around 1951.

In detail, if p is a prime number, \chi a nontrivial Dirichlet character modulo p, and

G(\chi)=\sum \chi(a) \zeta^a

where \zeta is a primitive p-th root of unity in the complex numbers, then

\frac{G(\chi)}{|G(\chi)|}

is a root of unity if and only if \chi is the quadratic residue symbol modulo p. The 'if' part was known to Gauss: the contribution of Chowla and Mordell was the 'only if' direction. The ratio in the theorem occurs in the functional equation of L-functions.

References

This article is issued from Wikipedia - version of the Saturday, April 20, 2013. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.