Radu Murgescu

Radu Murgescu
Ph.D. (2009) Cornell University

First Position



On the p-Class Groups of the Pure Number Field Q(N1/p) and its Galois Closure Q(N1/p, ζp)


Research Area:
Algebraic number theory

Abstract: We study the class groups of the fields K = Q(N1/p) and M = Q(N1/p, ζp), where N and p are primes and ζp is a primitive pth root of unity. Furthermore, we restrict ourselves to the study of the p-class groups, i.e. the Sylow p-subgroups of the class groups in question. We denote the p-class group of a field F by SF. Define rank(SF) as the dimension of SF / (SF)p as a vector space over Fp.

Frank Gerth III, in [9], settled a problem left open by F. Calegari and M. Emerton in [4]. He, in turn, posed a related question, which we answer in this thesis, as follows.

Theorem 3.15. Let N ≡ 4 or 7 (mod 9), and suppose 3 is a cubic residue (mod N). Then rank(SM) = 2.

For general values of p, we obtain results (Propositions 2.13, 4.1, 4.3, 5.2, 5.3, and 5.9) on the existence of certain norms in the extension M/Qp), and use these results to give bounds on rank(SM). For example, we show the following:

Proposition 5.2. Let p and N be any primes with p ≥ 5, N ≠ p, and let f denote the minimal positive integer x such that Nx ≡ 1 (mod p). Let U_Qp)+ be the real units of Qp). Suppose (p – 1)/f is odd. Then U_Qp)+ ⊆ N_{M/Qp)}(M*), where N_{M/Qp)} denotes the usual norm map of the extension M/Qp).