Progress Towards Counting D_5 Quintic Fields

TL;DR

This paper investigates bounds on the number of quintic fields with Galois group D_5, proposing a new approach using norm equations that suggests potential improvements over existing bounds.

Contribution

It introduces a novel method involving counting points on a variety defined by a norm equation to improve upper bounds on D_5 quintic fields.

Findings

Computer calculations support the bound of O(X^{2/3})

Reinterpretation of Wong's proof using norm equations

Potential for improved bounds on N(5,D_5,X)

Abstract

Let $N(5,D_5,X)$ be the number of quintic number fields whose Galois closure has Galois group $D_5$ and whose discriminant is bounded by $X$. By a conjecture of Malle, we expect that $N(5,D_5,X) \sim C X^{1/2}$ for some constant $C$. The best known upper bound is $N(5,D_5,X)\ll X^{3/4 + \epsilon}$, and we show this could be improved by counting points on a certain variety defined by a norm equation; computer calculations give strong evidence that this number is $\ll X^{2/3}$. Finally, we show how such norm equations can be helpful by reinterpreting an earlier proof of Wong on upper bounds for $A_4$ quartic fields in terms of a similar norm equation.