BEGIN:VCALENDAR
VERSION:2.0
PRODID:researchseminars.org
CALSCALE:GREGORIAN
X-WR-CALNAME:researchseminars.org
BEGIN:VEVENT
SUMMARY:João Vitor Pinto e Silva (U. Newcastle)
DTSTART:20210825T230000Z
DTEND:20210825T233000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/1
DESCRIPTION:Title: Infinite Matrices\nby João Vitor Pinto e Silva (U. Newcastle) as p
art of World of GroupCraft\n\n\nAbstract\nTo understand a theory\, it is a
lways good to work with objects that are easier to understand and work wit
h. With that in mind\, me and my supervisors developed a theory for infini
te matrices indexed by posets over a ring. On the presentation I will talk
about how to define these rings/groups\, how to write these groups/rings
as inverse limits of finite matrices rings\, isomorphism problems and new
simple totally disconnected groups that arise from the theory.\n \n\nThis
work is a generalization of the work done by Peter Groenhout\, Colin D. Re
id and George A. Willis: https://arxiv.org/pdf/1911.09956.pdf\n
LOCATION:https://researchseminars.org/talk/GroupCraft/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Junseok Kim (KAIST)
DTSTART:20210825T233000Z
DTEND:20210826T000000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/2
DESCRIPTION:Title: Non-relative hyperbolicity of automorphism and outer automorphism group
s of right-angled Artin groups\nby Junseok Kim (KAIST) as part of Worl
d of GroupCraft\n\n\nAbstract\nBehrstock\, Druţu\, and Mosher showed in t
heir paper that the general linear group $\\mathrm{GL}_n(\\mathbb{Z})$ wit
h $n\\geq 3$\, the automorphism group and the outer automorphism group of
a free group of finite rank at least 3 are not relatively hyperbolic. In t
his talk\, we show a generalized version of this theorem using a criterion
of non-relative hyperbolicity made by Anderson\, Aramayona\, and Shacklet
on. Our result is as follows: The automorphism groups of right-angled Arti
n groups whose defining graphs have at least 3 vertices are not relatively
hyperbolic. We also show that the outer automorphism groups are also not
relatively hyperbolic\, except for a few exceptional cases. In these cases
\, they are virtually isomorphic to one of the following: a finite group\,
an infinite cyclic group\, or $\\mathrm{GL}_2(\\mathbb{Z})$. (Joint with
Sangrok Oh and Philippe Tranchida)\n
LOCATION:https://researchseminars.org/talk/GroupCraft/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dmitry Berdinsky (Mahidol U.)
DTSTART:20210826T000000Z
DTEND:20210826T003000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/3
DESCRIPTION:Title: Normal Forms in Cayley Automatic Groups\nby Dmitry Berdinsky (Mahid
ol U.) as part of World of GroupCraft\n\n\nAbstract\nIn this talk I will d
iscuss the notion of a Cayley automatic group\, introduced by Kharlampovic
h\, Khoussainov and Miasnikov\, and some extensions of this notion. The ma
in focus will be on geometric and computational properties of normal forms
in such groups. My talk will be mainly based on these papers: https://arx
iv.org/abs/2008.02381 and https://arxiv.org/abs/2008.02511. If time allows
I will mention some results from https://arxiv.org/abs/1804.02548\, https
://arxiv.org/abs/1902.00652 and https://arxiv.org/abs/2001.04743\n
LOCATION:https://researchseminars.org/talk/GroupCraft/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xiaobing Sheng (U. Tokyo)
DTSTART:20210826T010000Z
DTEND:20210826T013000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/4
DESCRIPTION:Title: Divergence Properties of the Brown-Thompson's groups and the braided Th
ompson's groups\nby Xiaobing Sheng (U. Tokyo) as part of World of Grou
pCraft\n\n\nAbstract\nGolan and Sapir proved that the Thompson's groups $F
$\, $T$ and $V$ have linear divergence. In this talk\, we focus on the div
ergence properties of several generalisation of the Thompson's groups\, we
first consider the Brown-Thompson's groups $F_n$\, $T_n$ and $V_n$ and fo
und out that these groups also have linear divergence function. We then co
nsider the braided Thompson's groups $BF$ and $\\widehat{BF}$ and $\\wideh
at{BV}$ together with Kodama's result on the linear divergence of $BV$\, w
e conclude that the braided Thompson's groups have linear divergence.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tomoshige Yukita (Waseda U.)
DTSTART:20210826T013000Z
DTEND:20210826T020000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/5
DESCRIPTION:Title: Growth rates and spectral radii of Coxeter groups\nby Tomoshige Yuk
ita (Waseda U.) as part of World of GroupCraft\n\n\nAbstract\nThe growth r
ate $\\omega(G\,S)$ and spectral radius $\\lambda_{(\\Gamma\,S)}$ of a fin
itely generated group $(\\Gamma\,S)$ is a quantity related to the Cayley g
raph $\\text{Cay}(\\Gamma\,S)$ that measure complexity of $\\text{Cay}(\\G
amma\,S)$. In this talk\, we focus on Coxeter groups which are generalizat
ions of reflection groups. First\, we consider the space $\\mathcal{C}$ of
Coxeter groups which is the subspace in the space of marked groups consis
ting of Coxeter systems\, and show that $\\mathcal{C}$ is compact. Second\
, we prove that growth rates are continuous in $\\mathcal{C}$ and provide
examples of convergence and spectral radii of Coxeter groups.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Robert Tang (Xi'an Jiaotong-Liverpool U.)
DTSTART:20210826T020000Z
DTEND:20210826T023000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/6
DESCRIPTION:Title: Coarse vs fine geometry of the saddle connection graph\nby Robert T
ang (Xi'an Jiaotong-Liverpool U.) as part of World of GroupCraft\n\n\nAbst
ract\nThe saddle connection graph encodes intersection information regardi
ng saddle connections on a translation surface. This can be viewed as an i
nduced subgraph of the arc graph of the surface. A natural question to ask
is what we can deduce from either the isomorphism type or the quasi-isome
try type of the saddle connection graph. It turns out that there is a quit
e a difference between the fine and coarse geometry. Both parts are based
on joint work with Valentina Disarlo\, Huiping Pan\, and Anja Randecker.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Swathi Krishna (CEBS Mumbai)
DTSTART:20210826T033000Z
DTEND:20210826T040000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/7
DESCRIPTION:Title: Pullbacks of metric (graph) bundles and Cannon-Thurston maps\nby Sw
athi Krishna (CEBS Mumbai) as part of World of GroupCraft\n\n\nAbstract\nM
etric (graph) bundles were first defined by Mahan Mj and Pranab Sardar. Gi
ven a metric (graph) bundle $X$ over a hyperbolic space $B$ and a qi embed
ding $i: A\\to B$\, when $X$ and all the fibers are uniformly (Gromov) hyp
erbolic and nonelementary\, the pullback $Y$ of $X$ exists and is hyperbol
ic. Moreover\, a Cannon-Thurston map exists for the pullback map $i^*:Y \\
to X$. In this talk\, we discuss an application of this theorem which show
s that given a short exact sequence of nonelementary hyperbolic groups $1\
\to N\\to G\\stackrel{\\pi}{\\to} Q\\to 1$ and a finitely generated qi emb
edded subgroup $Q_1 < Q$\, $G_1:= \\pi^{-1}(Q_1)$ is hyperbolic and the in
clusion $G_1 \\hookrightarrow G$ admits a Cannon Thurston map $\\partial G
_1\\to \\partial G$. This is part of joint work with Pranab Sardar.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tushar Kanta Naik (IISER Mohali)
DTSTART:20210826T040000Z
DTEND:20210826T043000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/8
DESCRIPTION:Title: Automorphisms of three canonical extensions of symmetric groups\nby
Tushar Kanta Naik (IISER Mohali) as part of World of GroupCraft\n\n\nAbst
ract\nThe symmetric group $S_n$\, $n \\geq 2$\, has a Coxeter presentation
with generating set $X = \\{\\tau_1\, \\dots\, \\tau_{n-1}\\}$ and defini
ng relations\n\n(1) Involutions: $\\tau^2_i = 1$ for $1 \\leq i \\leq n
− 1$\;\n\n(2) Braid relations: $\\tau_i \\tau_{i+1} \\tau_i = \\tau_{i+1
} \\tau_i \\tau_{i+1}$ for $1 \\leq i \\leq n − 2$\;\n\n(3) Far commutat
ivity: $\\tau_i \\tau_j = \\tau_j \\tau_i$ for $|i − j|\\geq 2$.\n\nBy o
mitting all relations of type (1) (respectively type (2) ) from the preced
ing presentation of $S_n$\, we get presentations of the Artin braid group
$B_n$ (respectively the twin group $T_n$). Artin braid groups are well-stu
died objects with nice geometrical presentations in 3-space. Apart from ma
thematics\, they have far-reaching applications in physics and biology. Tw
in groups can be thought of as planar analogues of braid groups. Recently
these groups have attracted attention from (quantum) physicists. Thus\, it
is natural to ask about the remaining case. What kind of group do we get\
, if we omit all relations of the third type from the above presentation o
f $S_n$?\n\nIt follows that if we remove all relations of type (3)\, we ge
t an odd Coxeter group whose associated Coxeter graph is a straight line o
n $n − 1$ vertices. In this talk\, we will consider a general family of
odd Coxeter groups whose associated Coxeter graphs are trees\, discuss the
ir automorphism groups and compare with the automorphism groups of Artin b
raid groups and twin groups.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Neha Nanda (IISER Mohali)
DTSTART:20210826T043000Z
DTEND:20210826T050000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/9
DESCRIPTION:Title: Virtual twin groups and doodles on surfaces\nby Neha Nanda (IISER M
ohali) as part of World of GroupCraft\n\n\nAbstract\nThe study of certain
isotopy classes of a finite collection of immersed circles without triple
or higher intersections on closed oriented surfaces can be thought of as a
planar analogue of virtual knot theory where the genus zero case correspo
nds to classical knot theory. Alexander and Markov theorems for the genus
zero case are known\, where the role of groups is played by twin groups\,
a class of right-angled Coxeter groups with only far commutativity relatio
ns. In this talk\, I will discuss Alexander and Markov theorems for the hi
gher genus case\, where the role of groups is played by a new class of gro
ups called virtual twin groups. This is joint work with Dr Mahender Singh.
I will also address recent work on the structural aspects of these groups
\, which is joint work with Dr Mahender Singh and Dr Tushar Kanta Naik.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Soumya Dey (IMSc Chennai)
DTSTART:20210826T053000Z
DTEND:20210826T060000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/10
DESCRIPTION:Title: Liftable mapping class groups of regular cyclic covers\nby Soumya
Dey (IMSc Chennai) as part of World of GroupCraft\n\n\nAbstract\nWe shall
discuss a symplectic criterion for a mapping class to be liftable under a
regular cyclic cover of closed oriented surfaces\, and some of its interes
ting applications.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arghya Mondal (TIFR Mumbai)
DTSTART:20210826T060000Z
DTEND:20210826T063000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/11
DESCRIPTION:Title: Property (T) for fiber products\nby Arghya Mondal (TIFR Mumbai) as
part of World of GroupCraft\n\n\nAbstract\nProperty (T) is a representati
on-theoretic property of a group which has a strong influence on the geome
try and dynamics of its actions. A natural question for any property of a
group is whether it is retained when two groups with that property are com
bined in some way. In joint work with Mahan Mj\, we address this question
for Property (T) and fiber products. I will discuss a simple sufficient co
ndition\, as also equivalent conditions in a special case. Finally\, I wil
l give a few counterexamples\, including the case involving hyperbolically
embedded subgroups of a group with Property (T).\n
LOCATION:https://researchseminars.org/talk/GroupCraft/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ravi Tomar (IISER Mohali)
DTSTART:20210826T063000Z
DTEND:20210826T070000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/12
DESCRIPTION:Title: Boundaries of graphs of relatively hyperbolic groups with cyclic edge
groups\nby Ravi Tomar (IISER Mohali) as part of World of GroupCraft\n\
n\nAbstract\nLet $G(Y)$ be a graph of convergence groups with parabolic ed
ge groups and let $G$ be the fundamental group of $G(Y)$. First of all\, I
will discuss that $G$ is a convergence group. For that\, we explicitly co
nstruct a compact metrizable space on which $G$ acts as a convergence grou
p. I will try to give some details of the construction. Then I will discus
s combination theorems for a graph of relatively hyperbolic groups in two
situations: (1) When edge groups are parabolics and (2) when edge groups a
re cyclic. In both these situations\, we also have the construction of Bow
ditch boundaries.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Paul-Henry Leemann (U. Neuchâtel)
DTSTART:20210826T073000Z
DTEND:20210826T080000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/13
DESCRIPTION:Title: Wreath product of groups acting with bounded orbits\nby Paul-Henry
Leemann (U. Neuchâtel) as part of World of GroupCraft\n\n\nAbstract\nNum
erous interesting group properties admit a characterisation of the form "(
FS) = Every G-action on a S-space has a fixed point" fo some class S of me
tric spaces. In some cases\, this is equivalent to "(BS) = Every G-action
on a S-space has bounded orbits". For example\, if S = {real affine Hilber
t spaces} and G is countable\, then (BS)=(FS) is equivalent to Kazdhan's p
roperty (T). On the other hand\, if S = {trees}\, then (BS)=(FS) is Serre'
s property (FA).\nGiven a group property (P)\, it is natural to ask if it
is stable under classical group operations\, as products\, semi-direct pro
ducts or wreath products $G\\wr_X H$. I will give an unified and elementar
y proof of the fact that for numerous class S of metric spaces we have: $G
\\wr_X H$ has (BS) if and only if both G and H have S and X is finite.\n\n
Joint work with G. Schneeberger\n
LOCATION:https://researchseminars.org/talk/GroupCraft/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xiaolei Wu (U. Bielefeld)
DTSTART:20210826T080000Z
DTEND:20210826T083000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/14
DESCRIPTION:Title: Finiteness properties of asymptotic mapping class groups\nby Xiaol
ei Wu (U. Bielefeld) as part of World of GroupCraft\n\n\nAbstract\nAsympto
tic mapping class group of genus zero was first introduced by Funar and Ka
poudjian. It is a finitely presented group which contains the mapping clas
s groups of all genus zero surfaces. Later the definitions were generalize
d to allow the genus to be any finite number (Funar--Aramayona) or infinit
e (Funar--Kapoudjian). We will discuss how these groups are constructed
and show that they are in fact of type infinity.\n\nThis is based on joint
work with Javier Aramayona\, Kai-Uwe Bux\, Jonas Flechsig and Nansen Pet
rosyan.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yuri Santos Rego (U. Madgeburg)
DTSTART:20210826T083000Z
DTEND:20210826T090000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/15
DESCRIPTION:Title: Geometric conjugacy invariants and Thompson groups\nby Yuri Santos
Rego (U. Madgeburg) as part of World of GroupCraft\n\n\nAbstract\nDehn's
decision problems -- particularly the conjugacy problem -- have been drivi
ng forces in combinatorial and geometric group theory\, and history also t
ells us that conjugacy classes reveal useful information about groups. Two
broad questions arise: given a group\, can we describe its conjugacy clas
ses in a nice way and solve the conjugacy problem for it?\nIn this talk we
will discuss (or rather advertise) the use of geometry and combinatorics
to produce conjugacy invariants\, focusing in particular on Thompson group
s. We will then see how such tools yield a solution to the conjugacy probl
em for the braided version of Thompson's group V. (This is based on joint
work with Kai-Uwe Bux.)\n
LOCATION:https://researchseminars.org/talk/GroupCraft/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Federico Berlai (U. Vienna)
DTSTART:20210826T093000Z
DTEND:20210826T100000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/16
DESCRIPTION:Title: Automorphism groups of Cayley graphs of Coxeter groups\nby Federic
o Berlai (U. Vienna) as part of World of GroupCraft\n\n\nAbstract\nt is kn
own that automorphism groups of locally finite graphs admit a totally disc
onnected locally compact (tdlc) topology. In this talk I will present some
recent results concerning automorphism groups of a particular class of lo
cally finite graphs\, that is of Cayley graphs of Coxeter groups\, precise
ly characterising when these are not discrete. Particular attention will b
e given to the right-angled case.\n\nJoint work with Michal Ferov.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Shayo Olukoya (U. St Andrews)
DTSTART:20210826T100000Z
DTEND:20210826T103000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/17
DESCRIPTION:Title: Automorphism tower of groups of homeomorphism of Cantor space\nby
Shayo Olukoya (U. St Andrews) as part of World of GroupCraft\n\n\nAbstract
\nThe class of full and sufficiently transitive (i.e. flexible) groups of
homeomorphisms of Cantor space contains many groups of interest including
generalisations of the Higman-Thompson groups $G_{n\,r}$\, and the Ration
al group $R_2$ of Grigorchuk\, Nekrashevych\, and Suchanskiı̆. We will i
ntroduce this class of groups and go on to describe recent results on the
automorphism tower of such groups. For the groups $G_{n\,r}$ our result ca
n be seen as extending results of Brin and Guzmán for Thompson’s group
$T$ and generalisations of Thompson’s group $F$.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Giles Gardam (U Münster)
DTSTART:20210826T103000Z
DTEND:20210826T110000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/18
DESCRIPTION:Title: Diffuse groups\nby Giles Gardam (U Münster) as part of World of G
roupCraft\n\n\nAbstract\nThe unit conjecture for group rings is only known
to hold as a consequence of the mysterious "unique products property". In
this talk I'll discuss the group property of diffuseness\, which was intr
oduced by Bowditch as a geometric variation on unique products.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Naomi Andrew (U. Southampton)
DTSTART:20210826T120000Z
DTEND:20210826T123000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/19
DESCRIPTION:Title: Free-by-cyclic groups\, automorphisms\, and actions on trees\nby N
aomi Andrew (U. Southampton) as part of World of GroupCraft\n\n\nAbstract\
nFree-by-cyclic groups depend only on an automorphism of a free group\, bu
t detangling that information can be a challenge. We'll take a quick look
at some properties of free-by-cyclic groups\, and how they can vary with t
he defining automorphism. I'll then discuss our construction of particular
ly nice actions on trees for some free-by-cyclic groups\, and how we use t
hem to understand their outer automorphisms. (Joint with Armando Martino)\
n
LOCATION:https://researchseminars.org/talk/GroupCraft/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ihechukwu Chinyere (U. Essex)
DTSTART:20210826T123000Z
DTEND:20210826T130000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/20
DESCRIPTION:Title: Hyperbolic groups of Fibonacci type\nby Ihechukwu Chinyere (U. Ess
ex) as part of World of GroupCraft\n\n\nAbstract\nGroups of Fibonacci type
or more generally cyclically presented groups\, are groups that can be de
fined by a balanced presentation that admits a particular cyclic symmetry.
By building on previous results concerning hyperbolicity of groups of Fib
onacci type\, we classify the hyperbolic groups within this class\, except
for the two notoriously difficult Gilbert-Howie groups $H(9\,4)$ and $H(9
\,7)$. The main references are https://arxiv.org/abs/2006.09018 and https:
//arxiv.org/abs/2008.08986.\n\nIn this talk\, I will first define cyclical
ly presented groups (of Fibonacci type). Then\, I will describe the main r
esult and the ideas that go into the proof. This is joint work with Gerald
Williams.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Linton (U. Warwick)
DTSTART:20210826T130000Z
DTEND:20210826T133000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/21
DESCRIPTION:Title: Fibre products\, free groups and regular languages\nby Marco Linto
n (U. Warwick) as part of World of GroupCraft\n\n\nAbstract\nWe show that
the number of conjugacy classes of intersections $A\\cap B^g$ for finitely
generated subgroups $A\, B < F$ of a free group $F$ is bounded above in t
erms of the ranks of $A$ and $B$\, confirming an intuition of Walter Neuma
nn. This result was previously known only in the case where $A$ is cyclic
by the $w$-cycles theorem of Helfer and Wise and\, independently\, Louder
and Wilton. The main tools I will present will be results regarding the st
ructure of fibre products of finite graphs. I will also show how such tool
s lead to a new algorithm to decide non-emptiness of the intersection of t
wo regular languages.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marialaura Noce (U. Göttingen)
DTSTART:20210826T143000Z
DTEND:20210826T150000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/23
DESCRIPTION:Title: Ramification structures for quotients of the Grigorchuk groups\nby
Marialaura Noce (U. Göttingen) as part of World of GroupCraft\n\n\nAbstr
act\nGroups of automorphisms of regular rooted trees have been studied for
years as an important source of groups with interesting properties. For e
xample\, the Grigorchuk groups provide a family of groups with intermediat
e word growth and the torsion Grigorchuk groups constitute a counterexampl
e to the General Burnside Problem. For these groups there is a natural fam
ily of normal subgroups of finite index\, which are the level stabilizers.
The goal of this talk is to show that the quotients by such subgroups adm
it a ramification structure. Roughly speaking\, groups of surfaces isogeno
us to a higher product of curves are characterised by the existence of a r
amification structure. Recall that an algebraic surface $S$ is isogenous t
o a higher product of curves if it is isomorphic to $(C_1 \\times C_2)/G$\
, where $C_1$ and $C_2$ are curves of genus at least $2$\, and $G$ is a fi
nite group acting freely on $C_1 \\times C_2$.\n\nIn this talk\, we first
introduce the Grigorchuk groups and then we show that their quotients admi
t ramification structures\, providing the first explicit infinite family o
f $3$-generated finite $2$-groups with ramification structures that are no
t Beauville. This is joint work with A. Thillaisundaram.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bin Sun (U. Oxford)
DTSTART:20210826T140000Z
DTEND:20210826T143000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/24
DESCRIPTION:Title: Wreath-like products of groups and rigidity of their von Neumann algeb
ras\nby Bin Sun (U. Oxford) as part of World of GroupCraft\n\n\nAbstra
ct\nWe provide the first positive examples to the Conne’s Rigidity Conje
cture which states that if a group $G$ has Kazhdan’s property $(T)$ and
the infinite conjugacy class property\, then $G$ is von Neumann rigid\, i.
e.\, whenever $H$ is a group whose von Neumann algebra is isomorphic to th
at of $G$\, one has $H$ isomorphic to $G$. Our examples are certain genera
lized wreath-product groups\, which arise naturally from Dehn fillings of
hyperbolically embedded subgroups. This is a joint work with Ionut Chifan\
, Adrian Ioana and Denis Osin.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ignat Soroko (Florida State U.)
DTSTART:20210826T160000Z
DTEND:20210826T163000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/25
DESCRIPTION:Title: Commensurability of spherical Artin groups\nby Ignat Soroko (Flori
da State U.) as part of World of GroupCraft\n\n\nAbstract\nTwo groups are
commensurable if some subgroups of finite index in them are isomorphic to
each other. This gives us an equivalence relation on groups which is coars
er than isomorphism but finer than quasi-isometry. Cumplido and Paris star
ted the program of classification of Artin groups of spherical type up to
commensurability. They completely described when such a group is commensur
able with an Artin group of type $A_n$ (braid group). To solve the problem
of commensurability in full\, six remaining (hard) cases need to be resol
ved\, for the Artin groups of the types: $(D_4\,F_4)$\, $(D_4\,H_4)$\, $(F
_4\,H_4)$\, $(D_6\,E_6)$\, $(D_7\,E_7)$\, $(D_8\,E_8)$. In my recent artic
le\, I settled the first two cases\, i.e. I proved that the Artin group of
type $D_4$ is not commensurable with those of types $F_4$ and $H_4$. I wi
ll give a short introduction into the concepts involved and methods used i
n the proof.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Rylee Lyman (Rutgers U.–Newark)
DTSTART:20210826T163000Z
DTEND:20210826T170000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/26
DESCRIPTION:Title: Exploring the spine of Outer Space for free products\nby Rylee Lym
an (Rutgers U.–Newark) as part of World of GroupCraft\n\n\nAbstract\nIn
a seminal paper\, Culler and Vogtmann defined a space now called Outer Spa
ce for the outer automorphism group of a free group to act on. Their main
result is that Outer Space is contractible. They prove this by exhibiting
a simplicial spine onto which Outer Space deformation retracts and giving
a combinatorial Morse-theoretic proof that the spine is contractible. Guir
ardel and Levitt define an Outer Space for a countable group that splits a
s a free product and give a different\, folding-type argument to show dire
ctly that their Outer Space is contractible. The purpose of this talk is t
o develop the theory of the spine of Guirardel–Levitt Outer Space. Our m
ain result is the combinatorial proof that the spine is contractible. In f
uture work we would like to apply this study to show that the spine is sim
ply connected at infinity.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abdul Zalloum (Queens U.)
DTSTART:20210826T170000Z
DTEND:20210826T173000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/27
DESCRIPTION:Title: Regular languages for hyperbolic-like geodesics\nby Abdul Zalloum
(Queens U.) as part of World of GroupCraft\n\n\nAbstract\nA classic theore
m by Cannon states that geodesics in hyperbolic groups form a regular lang
uage. Intuitively\, this means that geodesics in hyperbolic groups satisfy
a strong recursive structure allowing one to prove various results regard
ing the growth of such groups. I will state Cannons theorem\, discuss it's
connection to the growth of hyperbolic groups and their subgroups\, and s
tate various generalizations of Cannon's work to ``hyperbolic-like" geodes
ics in other groups.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mark Pengitore (U. Virginia)
DTSTART:20210826T180000Z
DTEND:20210826T183000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/28
DESCRIPTION:Title: Effective onjugacy separabity for lamplighter groups\nby Mark Peng
itore (U. Virginia) as part of World of GroupCraft\n\n\nAbstract\nGiven a
finitely generated group\, one can make conjugacy separability effective b
y measuring how deep within the lattice of normal subgroups of finite inde
x one needs to go in order to be able to decide whether two elements are c
onjugate. In this talk I will sketch a proof that lamplighter groups have
exponential conjugacy depth function.(Joint with Michal Ferov)\n
LOCATION:https://researchseminars.org/talk/GroupCraft/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jesús Hernández Hernández (UNAM\, Campus Morelia)
DTSTART:20210826T183000Z
DTEND:20210826T190000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/29
DESCRIPTION:Title: Rigidity phenomena of mapping class groups\nby Jesús Hernández H
ernández (UNAM\, Campus Morelia) as part of World of GroupCraft\n\n\nAbst
ract\nThe mapping class group of a surface presents several peculiarities
when one studies its actions on some natural objects\, in particular its a
ction on itself by conjugation and on the curve graph by automorphisms. In
this talk we explore these actions and what do we actually mean by rigidi
ty for them. Finally\, we give a way to relate the mapping class group and
the curve graph of a surface with Artin-Tits groups and their parabolic s
ubgroup graph\, posing several questions relating to the concept of rigidi
ty.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Radhika Gupta (Temple U.)
DTSTART:20210826T190000Z
DTEND:20210826T193000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/30
DESCRIPTION:Title: From buildings to factor complex\nby Radhika Gupta (Temple U.) as
part of World of GroupCraft\n\n\nAbstract\nWe will consider three families
of groups - arithmetic groups\, mapping class groups and groups of outer
automorphisms of a free group. The study of arithmetic groups has had a pr
ofound influence on how we understand the latter two classes of groups. In
this talk\, we will specifically draw parallels between the associated si
mplicial complexes - Tits building\, curve complex and free factor complex
- from a topological point of view. This joint work with Benjamin Brück.
\n
LOCATION:https://researchseminars.org/talk/GroupCraft/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Slobodan Tanushevski (Fluminense Federal U.)
DTSTART:20210826T200000Z
DTEND:20210826T203000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/31
DESCRIPTION:Title: Retracts of free groups\nby Slobodan Tanushevski (Fluminense Feder
al U.) as part of World of GroupCraft\n\n\nAbstract\nA subgroup $R$ of a g
roup $G$ is said to be a retract of $G$ if there exists a homomorphism $r
\\colon G \\rightarrow R$ (called a retraction) that restricts to the iden
tity on $R$.\n\nAn element $g$ of a group $G$ is called a test element if
every endomorphism of $G$ that fixes $g$ is an automorphism.\n\nIn this ta
lk\, I will discuss some recent results on test elements and retracts of f
ree groups (the two concepts are closely related).\n
LOCATION:https://researchseminars.org/talk/GroupCraft/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sami Douba (McGill U.)
DTSTART:20210826T203000Z
DTEND:20210826T210000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/32
DESCRIPTION:Title: Proper CAT(0) actions of unipotent-free linear groups\nby Sami Dou
ba (McGill U.) as part of World of GroupCraft\n\n\nAbstract\nButton observ
ed that finitely generated linear groups containing no nontrivial unipoten
t matrices behave much like groups admitting proper actions by semisimple
isometries on complete $\\operatorname{CAT}(0)$ spaces. It turns out that
any finitely generated linear group possesses an action on such a space wh
ose restrictions to unipotent-free subgroups are in some sense tame. We di
scuss some implications of this phenomenon for the representation theory o
f $3$-manifold groups.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ash DeClerk (U. Nebraska–Lincoln)
DTSTART:20210826T220000Z
DTEND:20210826T223000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/34
DESCRIPTION:Title: Groups with the Falsification by Fellow Traveler Property are Autostac
kable\nby Ash DeClerk (U. Nebraska–Lincoln) as part of World of Grou
pCraft\n\n\nAbstract\nFalsification by fellow traveler property (FFTP) is
a purely geometric property introduced by Neumann and Shapiro in 1987\; ma
ny groups\, including virtually abelian groups\, word hyperbolic groups\,
Coxeter groups\, Artin groups of large type\, and Garside groups have FFTP
. Autostackable structures\, introduced by Brittenham\, Hermiller\, and Ho
lt in 2013\, generalize both automatic normal forms and an algorithm to re
duce any word to its normal form. In this talk\, I will show that all grou
ps with FFTP also have an autostackable structure with geodesic normal for
ms.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arman Darbinyan (Texas A&M U.)
DTSTART:20210826T223000Z
DTEND:20210826T230000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/35
DESCRIPTION:Title: Computability properties of left- and bi-orderable groups\nby Arma
n Darbinyan (Texas A&M U.) as part of World of GroupCraft\n\n\nAbstract\nA
n important class of abstract groups is the one that consists of linearly
ordered groups whose orders are invariant under left (and right) group mul
tiplications. From computability point of view it is interesting to invest
igate when orderable groups admit computable orders. In particular\, a que
stion of Downey and Kurtz asks about existence of computable orderable gro
ups that do not admit computable orders with respect to any group presenta
tion. In my talk I will discuss recent advancements on this topic.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicolas Brody (U. California\, Berkeley)
DTSTART:20210826T210000Z
DTEND:20210826T213000Z
DTSTAMP:20260414T224314Z
UID:GroupCraft/36
DESCRIPTION:Title: Groups acting on trees via number theory\nby Nicolas Brody (U. Cal
ifornia\, Berkeley) as part of World of GroupCraft\n\n\nAbstract\nTrees ar
e fundamental objects in geometric group theory. Constructing a nontrivial
action of a group on a tree is akin to finding some tree-like structure o
n the group itself\, decomposing the group into possibly simpler groups. S
erre gave an arithmetic construction of group actions on trees\; we descri
be this construction in a hands-on way that is easy to compute with\, and
describe how various arithmetic facts can offer interesting results in gro
up theory and topology.\n
LOCATION:https://researchseminars.org/talk/GroupCraft/36/
END:VEVENT
END:VCALENDAR