# Kummer hypothesis

A hypothesis concerning the behaviour of the cubic Gauss sum

$$\tau(\chi)=\sum_{n=0}^{p-1}\chi(n,p)e^{\pi in/p},$$

where $\chi(n,p)=\exp(2\pi i\operatorname{ind}n/3)$ is a cubic character modulo $p\equiv1$ ($\bmod3$) and $p$ is a prime number. It is known that

$$\tau(\chi)=\sqrt pe^{i\arg\tau(\chi)}.$$

Therefore $\arg\tau(\chi)$ lies either in the first, third or fifth sextant. Accordingly, E. Kummer divided all primes $p\equiv1$ ($\bmod\,3$) into three classes, $P_1$, $P_3$ and $P_5$. The Kummer hypothesis is that each of the classes $P_1$, $P_5$ and $P_3$ contains infinitely many primes, and that their respective asymptotic densities are $1/2$, $1/3$ and $1/6$. There are various generalizations of the Kummer hypothesis to characters of order higher than 3. A modified version of the hypothesis has been proved (see [3]).

#### References

[1] | H. Hasse, "Vorlesungen über Zahlentheorie" , Springer (1950) |

[2] | H. Davenport, "Multiplicative number theory" , Springer (1980) |

[3] | D.R. Heath-Brown, S.I. Patterson, "The distribution of Kummer sums at prime arguments" J. Reine Angew. Math. , 310 (1979) pp. 111–130 |

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Kummer hypothesis.

*Encyclopedia of Mathematics.*URL: http://www.encyclopediaofmath.org/index.php?title=Kummer_hypothesis&oldid=34132