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Andrei Jaikin-Zapirain

Publications and source records attributed to Andrei Jaikin-Zapirain.

29 records · Page 2Linked to original sources
arXiv2015

Units of group rings, the Bogomolov multiplier, and the fake degree conjecture

Let $π$ be a finite $p$-group and $\mathbb{F}_q$ a finite field with $q=p^n$ elements. Denote by $\mathrm{I}_{\mathbb{F}_q}$ the augmentation ideal of the group ring $\mathbb{F}_q[π]$. We have found a surprising relation between the abelianization of $1+\mathrm{I}_{\mathbb{F}_q}$, the Bogomolov multiplier $\mathrm{B}_0(π)$ of $π$ and the number of conjugacy classes $\mathrm{k}(π)$ of $π$: \[ | (1+\mathrm{I}_{\mathbb{F}_q})_{\mathrm{ab}} |=q^{\mathrm{k}(π)-1}|\mathrm{B}_0(π)|. \] In particular, if $π$ is a finite $p$-group with a non-trivial Bogomolov multiplier, then $1+\mathrm{I}_{\mathbb{F}_q}$ is a counterexample to the fake degree conjecture proposed by M. Isaacs.

math.GR↗
arXiv2014

Finite p-groups with small automorphism group

For each prime $p$ we construct a family $\{G_i\}$ of finite $p$-groups such that $|\Aut (G_i)|/|G_i|$ goes to $0$, as $i$ goes to infinity. This disproves a well-known conjecture that $|G|$ divides $|\Aut(G)|$ for every non-abelian finite $p$-group $G$.

math.GR↗
arXiv2014

Property (T) for groups graded by root systems

We introduce and study the class of groups graded by root systems. We prove that if Φ is an irreducible classical root system of rank at least 2 and G is a group graded by Φ, then under certain natural conditions on the grading, the union of the root subgroups is a Kazhdan subset of G. As the main application of this theorem we prove that for any reduced irreducible classical root system Φ of rank at least 2 and a finitely generated commutative ring R with 1, the Steinberg group St_Φ(R) and the elementary Chevalley group E_Φ(R) have property (T). We also show that there exists a group with property (T) which maps onto all finite simple groups of Lie type and rank at least 2, thereby providing a "unified" proof of expansion in these groups.

math.GR↗
arXiv2013

The representation zeta function of a FAb compact p-adic Lie group vanishes at -2

Let G by compact p-adic Lie group and suppose that G is FAb, i.e., that H/[H,H] is finite for every open subgroup H of G. The representation zeta function Z(G,s) encodes the distribution of continuous irreducible complex characters of G. Here s denotes a complex variable and Z(G,s) is defined as the Dirichlet generating function whose nth coefficient is equal to the number of irreducible characters of G of degree n. For p greater than 2 it is known that Z(G,s) defines a meromorphic function on the complex plane. Wedderburn's structure theorem for semisimple algebras implies that ZG,-2) = |G| for finite G. We complement this classic result by proving that Z(G,-2) = 0 for infinite G, assuming that p is greater than 2.

math.GR↗
arXiv2011

Kazhdan quotients of Golod-Shafarevich groups

The main goal of this paper is to prove that every Golod-Shafarevich group has an infinite quotient with Kazhdan's property $(T)$. In particular, this gives an affirmative answer to the well-known question about non-amenability of Golod-Shafarevich groups.

math.GR↗
arXiv2011

Groups of positive weighted deficiency and their applications

In this paper we introduce the concept of weighted deficiency for abstract and pro-$p$ groups and study groups of positive weighted deficiency which generalize Golod-Shafarevich groups. In order to study weighted deficiency we introduce weighted versions of the notions of rank for groups and index for subgroups and establish weighted analogues of several classical results in combinatorial group theory, including the Schreier index formula. Two main applications of groups of positive weighted deficiency are given. First we construct infinite finitely generated residually finite $p$-torsion groups in which every finitely generated subgroup is either finite or of finite index -- these groups can be thought of as residually finite analogues of Tarski monsters. Second we develop a new method for constructing just-infinite groups (abstract or pro-$p$) with prescribed properties; in particular, we show that graded group algebras of just-infinite groups can have exponential growth. We also prove that every group of positive weighted deficiency has a hereditarily just-infinite quotient. This disproves a conjecture of Boston on the structure of quotients of certain Galois groups and solves Problem~15.18 from Kourovka notebook.

math.GR↗
arXiv2011

Normal Subgroups of Profinite Groups of Non-negative Deficiency

We initiate the study of profinite groups of non-negative deficiency. The principal focus of the paper is to show that the existence of a finitely generated normal subgroup of infinite index in a profinite group $G$ of non-negative deficiency gives rather strong consequences for the structure of $G$. To make this precise we introduce the notion of $p$-deficiency ($p$ a prime) for a profinite group $G$. This concept is more useful in the study of profinite groups then the notion of deficiency. We prove that if the $p$-deficiency of $G$ is positive and $N$ is a finitely generated normal subgroup such that the $p$-Sylow subgroup of $G/N$ is infinite and $p$ divides the order of $N$ then we have $\cd_p(G)=2$, $\cd_p(N)=1$ and $\vcd_p(G/N)=1$ for the cohomological $p$-dimensions; moreover either the $p$-Sylow subgroup of $G/N$ is virtually cyclic or the $p$-Sylow subgroup of $N$ is cyclic. A profinite Poincaré duality group $G$ of dimension 3 at a prime $p$ ($PD^3$-group) has deficiency 0. In this case we show that for $N$ and $p$ as above either $N$ is $PD^1$ at $p$ and $G/N$ is virtually $PD^2$ at $p$ or $N$ is $PD^2$ at $p$ and $G/N$ is virtually $PD^1$ at $p$. In particular if $G$ is pro-$p$ then either $N$ is infinite cyclic and $G/N$ is virtually Demushkin or $N$ is Demushkin and $G/N$ is virtually infinite cyclic. We apply this results to deduce structural information on the profinite completions of ascending HNN-extensions of free groups. We also give some implications of our theory to the congruence kernels of certain arithmetic groups.

math.GR↗
arXiv2011

The rank gradient from a combinatorial viewpoint

This paper investigates the asymptotic behaviour of the minimal number of generators of finite index subgroups in residually finite groups. We analyze three natural classes of groups: amenable groups, groups possessing an infinite soluble normal subgroup and virtually free groups. As a tool for the amenable case we generalize Lackenby's trichotomy theorem on finitely presented groups.

math.GR↗
arXiv2009

Property $(T)$ for noncommutative universal lattices

We establish a new spectral criterion for Kazhdan's property $(T)$ which is applicable to a large class of discrete groups defined by generators and relations. As the main application, we prove property $(T)$ for the groups $EL_n(R)$, where $n\geq 3$ and $R$ is an arbitrary finitely generated associative ring. We also strengthen some of the results on property $(T)$ for Kac-Moody groups from a paper of Dymara and Januszkiewicz (Invent. Math 150 (2002)).

math.GR↗