A Cubic analogue of the Friedlander-Iwaniec spin over primes

Abstract

In 1998 Friedlander and Iwaniec proved that there are infinitely many primes of the form $a^2+b^4$. To show this they defined the spin of Gaussian integers by the Jacobi symbol, and one of the key ingredients in the proof was to show that the spin becomes equidistributed along Gaussian primes. To generalize this we define the cubic spin of ideals of $\mathbb{Z}[\zeta_{12}]=\mathbb{Z}[\zeta_3,i]$ by using the cubic residue character on the Eisenstein integers $\mathbb{Z}[\zeta_3]$. Our main theorem says that the cubic spin is equidistributed along prime ideals of $\mathbb{Z}[\zeta_{12}]$. The proof of this follows closely along the lines of Friedlander and Iwaniec. The main new feature in our case is the infinite unit group, which means that we need to show that the definition of the cubic spin on the ring of integers lifts to a well-defined function on the ideals. We also explain how the cubic spin arises if we consider primes of the form $a^2+b^6$ on the Eisenstein integers.