Galois trace forms of type $A_{n}, D_{n}, E_{n}$ for odd $n$
Abstract
Let be an odd prime number and . Then, it is well-known that the -root lattice can be realized as the (Hermitian) trace form of the -th cyclotomic extension restricted to the fractional ideal generated by . In this paper, in contrast with the case of the -root lattice, we prove the following theorem: Let be an odd positive integer and be a Galois extension of degree . Then, there exist no fractional ideals of such that the restricted trace form is of type . The proof is done by the prime ideal factorization of fractional ideals of with care of certain 2-adic obstruction. Additionally, we prove that every cyclic cubic field contains infinitely many distinct sub -lattices of type (i.e., normalized face centered cubic lattices) with normal -bases. The latter fact is in contrast with another fact that among quadratic fields only contain sub -lattices of type .
Keywords
Cite
@article{arxiv.2307.06612,
title = {Galois trace forms of type $A_{n}, D_{n}, E_{n}$ for odd $n$},
author = {Riku Higa and Yoshinosuke Hirakawa},
journal= {arXiv preprint arXiv:2307.06612},
year = {2023}
}