D. - S. Kang, Z. Reichstein, Trace forms of Galois field extensions in the presence of roots of unity , J. Reine Angew. Math., 549 (2002), 79--89.

Abstract: Let L/K be a G-Galois field extension and let G_2 be a Sylow subgroup of G. We show that if G_2 is not abelian then the trace form of L/K is hyperbolic, provided that K contains certain roots of unity.

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