No Arabic abstract
Let $hat{F}$ be a free pro-$p$ non-abelian group, and let $Delta$ be a commutative Noetherian complete local ring with a maximal ideal $I$ such that $textrm{char}(Delta/I)=p>0$. In [Zu], Zubkov showed that when $p eq2$, the pro-$p$ congruence subgroup $$GL_{2}^{1}(Delta)=ker(GL_{2}(Delta)overset{DeltatoDelta/I}{longrightarrow}GL_{2}(Delta/I))$$ admits a pro-$p$ identity, i.e., there exists an element $1 eq winhat{F}$ that vanishes under any continuous homomorphism $hat{F}to GL_{2}^{1}(Delta)$. In this paper we investigate the case $p=2$. The main result is that when $textrm{char}(Delta)=2$, the pro-$2$ group $GL_{2}^{1}(Delta)$ admits a pro-$2$ identity. This result was obtained by the use of trace identities that originate in PI-theory.
We initiate an investigation of lattices in a new class of locally compact groups, so called locally pro-$p$-complete Kac-Moody groups. We discover that in rank 2 their cocompact lattices are particularly well-behaved: under mild assumptions, a cocompact lattice in this completion contains no elements of order $p$. This statement is still an open question for the Caprace-Remy-Ronan completion. Using this, modulo results of Capdeboscq and Thomas, we classify edge-transitive cocompact lattices and describe a cocompact lattice of minimal covolume.
We study 3-dimensional Poincare duality pro-$p$ groups in the spirit of the work by Robert Bieri and Jonathan Hillmann, and show that if such a pro-$p$ group $G$ has a nontrivial finitely presented subnormal subgroup of infinite index, then either the subgroup is cyclic and normal, or the subgroup is cyclic and the group is polycyclic, or the subgroup is Demushkin and normal in an open subgroup of $G$. Also, we describe the centralizers of finitely generated subgroups of 3-dimensional Poincare duality pro-$p$ groups.
The authors have shown previously that every locally pro-p contraction group decomposes into the direct product of a p-adic analytic factor and a torsion factor. It has long been known that p-adic analytic contraction groups are nilpotent. We show here that the torsion factor is nilpotent too, and hence that every locally pro-p contraction group is nilpotent.
We completely describe the finitely generated pro-$p$ subgroups of the profinite completion of the fundamental group of an arbitrary $3$-manifold. We also prove a pro-$p$ analogue of the main theorem of Bass--Serre theory for finitely generated pro-$p$ groups.
We show that for every finitely generated closed subgroup $K$ of a non-solvable Demushkin group $G$, there exists an open subgroup $U$ of $G$ containing $K$, and a continuous homomorphism $tau colon U to K$ satisfying $tau(k) = k$ for every $k in K$. We prove that the intersection of a pair of finitely generated closed subgroups of a Demushkin group is finitely generated (giving an explicit bound on the number of generators). Furthermore, we show that these properties of Demushkin groups are preserved under free pro-$p$ products, and deduce that Howsons theorem holds for the Sylow subgroups of the absolute Galois group of a number field. Finally, we confirm two conjectures of Ribes, thus classifying the finitely generated pro-$p$ M. Hall groups.