Mild pro-p-groups with 4 generators

Let p be an odd prime and S a finite set of primes = 1 mod p. We give an effective criterion for determining when the Galois group G=G_S(p) of the maximal p-extension of Q unramified outside of S is mild when |S|=4 and the cup product H^1(G,Z/pZ) \otimes H^1(G,Z/pZ) --> H^2(G,Z/pZ) is surjective.Comment: 12 pages. No figures. LaTe

Mild pro-2-groups and 2-extensions of Q with restricted ramification

Using the mixed Lie algebras of Lazard, we extend the results of the first author on mild groups to the case p=2. In particular, we show that for any finite set S_0 of odd rational primes we can find a finite set S of odd rational primes containing S_0 such that the Galois group of the maximal 2-extension of Q unramified outside S is mild. We thus produce a projective system of such Galois groups which converge to the maximal pro-2-quotient of the absolute Galois group of \Q unramified at 2 and $\infty$. Our results also allow results of Alexander Schmidt on pro-p-fundamental groups of marked arithmetic curves to be extended to the case p=2 over a global field which is either a function field of odd characteristic or a totally imaginary number field

Demuskin groups, Galois modules, and the elementary type conjecture

Let p be a prime and F(p) the maximal p-extension of a field F containing a primitive p-th root of unity. We give a new characterization of Demuskin groups among Galois groups Gal(F(p)/F) when p=2, and, assuming the Elementary Type Conjecture, when p>2 as well. This characterization is in terms of the structure, as Galois modules, of the Galois cohomology of index p subgroups of Gal(F(p)/F).Comment: v2 (20 pages); added theorem characterizing decompositions into free and trivial modules; to appear in J. Algebr

Remark on fundamental groups and effective Diophantine methods for hyperbolic curves

In a letter from Grothendieck to Faltings, it was suggested that a positive answer to the section conjecture should imply finiteness of points on hyperbolic curves over number fields. In this paper, we point out instead the analogy between the section conjecture and the finiteness conjecture for the Tate-Shafarevich group of elliptic curves. That is, the section conjecture should provide a terminating algorithm for finding all rational points on a hyperbolic curve equipped with a rational point