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SUMMARY:Sam Shepherd (University of Oxford)
DTSTART;VALUE=DATE-TIME:20200909T190000Z
DTEND;VALUE=DATE-TIME:20200909T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/1
DESCRIPTION:Title: Quasi-isometric rigidity of generic cyclic HNN extensio
ns of free groups\nby Sam Shepherd (University of Oxford) as part of McGil
l geometric group theory seminar\n\n\nAbstract\nStudying quasi-isometries
between groups is a major theme in geometric group theory. Of particular i
nterest are the situations where the existence of a quasi-isometry between
two groups implies that the groups are equivalent in a stronger algebraic
sense\, such as being commensurable. I will survey some results of this t
ype\, and then talk about recent work with Daniel Woodhouse where we prove
quasi-isometric rigidity for certain graphs of virtually free groups\, wh
ich include "generic" cyclic HNN extensions of free groups.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikołaj Frączyk (University of Chicago)
DTSTART;VALUE=DATE-TIME:20200916T190000Z
DTEND;VALUE=DATE-TIME:20200916T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/2
DESCRIPTION:Title: Growth of mod-p homology in higher rank lattices\nby Mi
kołaj Frączyk (University of Chicago) as part of McGill geometric group
theory seminar\n\n\nAbstract\nIt is known since the late 70s that in local
ly symmetric spaces of large injectivity radius\, the $k$-th real Betti nu
mber divided by the volume is approximately equal to the $k$-th $L^2$ Bett
i number. Is there an analogue of this fact for mod-$p$ Betti numbers? Thi
s question is still very far from being solved\, except for certain specia
l families of locally symmetric spaces. In this talk\, I want to advertise
a relatively new approach to study the growth of mod-$p$ Betti numbers ba
sed on a quantitative description of minimal area representatives of mod-$
p$ homology classes.\n
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BEGIN:VEVENT
SUMMARY:Michael Lipnowski (McGill University)
DTSTART;VALUE=DATE-TIME:20200923T190000Z
DTEND;VALUE=DATE-TIME:20200923T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/3
DESCRIPTION:Title: Algorithms for building grids\nby Michael Lipnowski (Mc
Gill University) as part of McGill geometric group theory seminar\n\n\nAbs
tract\nI'll describe an effective method to build grids in many metric spa
ces of interest in geometric group theory\, e.g. locally symmetric spaces.
Joint work with Aurel Page.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Duncan McCoy (Université du Québec à Montréal)
DTSTART;VALUE=DATE-TIME:20200930T190000Z
DTEND;VALUE=DATE-TIME:20200930T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/4
DESCRIPTION:Title: Characterizing slopes for torus knots and hyperbolic kn
ots\nby Duncan McCoy (Université du Québec à Montréal) as part of McGi
ll geometric group theory seminar\n\n\nAbstract\nA slope $p/q$ is a charac
terizing slope for a knot $K$ in the $3$-sphere if the oriented homeomorph
ism type of $p/q$-surgery on $K$ determines $K$ uniquely. It is known that
for a given torus knot all but finitely many non-integer slopes are chara
cterizing and that for hyperbolic knots all but finitely many slopes with
$q>2$ are characterizing. I will discuss the proofs of these results\, whi
ch have a surprising amount in common.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Robert Kropholler (WWU Münster)
DTSTART;VALUE=DATE-TIME:20201007T190000Z
DTEND;VALUE=DATE-TIME:20201007T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/5
DESCRIPTION:Title: Groups of type $FP_2$ over fields\nby Robert Kropholler
(WWU Münster) as part of McGill geometric group theory seminar\n\n\nAbst
ract\nBeing of type $FP_2$ is an algebraic shadow of being finitely presen
ted. A long standing question was whether these two classes are equivalent
. This was shown to be false in the work of Bestvina and Brady. More recen
tly\, there are many new examples of groups of type $FP_2$ coming with var
ious interesting properties. I will begin with an introduction to the fini
teness property $FP_2$. I will end by giving a construction to find groups
that are of type $FP_2(\\mathbb{F})$ for all fields $\\mathbb{F}$ but not
$FP_2(\\mathbb{Z})$.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Thomas Haettel (Université de Montpellier)
DTSTART;VALUE=DATE-TIME:20201014T190000Z
DTEND;VALUE=DATE-TIME:20201014T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/6
DESCRIPTION:Title: The coarse Helly property\, hierarchical hyperbolicity\
, and semihyperbolicity\nby Thomas Haettel (Université de Montpellier) as
part of McGill geometric group theory seminar\n\n\nAbstract\nFor any hier
archically hyperbolic group\, and in particular any mapping class\ngroup\,
we define a new metric that satisfies a coarse Helly property. This\nenab
les us to deduce that the group is semihyperbolic\, i.e. that it admits\na
bounded quasigeodesic bicombing\, and also that it has finitely many\ncon
jugacy classes of finite subgroups. This has several other consequences\nf
or the group. This is a joint work with Nima Hoda and Harry Petyt.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Asaf Hadari (University of Hawaii at Manoa)
DTSTART;VALUE=DATE-TIME:20201021T190000Z
DTEND;VALUE=DATE-TIME:20201021T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/7
DESCRIPTION:Title: Mapping class groups that do not virtually surject to t
he integers\nby Asaf Hadari (University of Hawaii at Manoa) as part of McG
ill geometric group theory seminar\n\n\nAbstract\nMapping class groups of
surfaces of genus at least 3 are perfect\, but their finite-index subgroup
s need not be&mdash\;they can have non-trivial abelianizations. A well-kno
wn conjecture of Ivanov states that a finite-index subgroup of a mapping c
lass group of a sufficiently high\ngenus has finite abelianization. We wil
l discuss a proof of this conjecture\, which goes through an equivalent re
presentation-theoretic form of the conjecture due to Putman and Wieland.\n
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BEGIN:VEVENT
SUMMARY:Ian Runnels (University of Virginia)
DTSTART;VALUE=DATE-TIME:20201028T190000Z
DTEND;VALUE=DATE-TIME:20201028T200000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/8
DESCRIPTION:Title: RAAGs in MCGs\nby Ian Runnels (University of Virginia)
as part of McGill geometric group theory seminar\n\n\nAbstract\nWe give a
new proof of a theorem of Koberda which says that right-angled Artin subgr
oups of mapping class groups abound. This alternative approach uses the hi
erarchical structure of the curve complex\, which allows for more explicit
computations. Time permitting\, we will also discuss some applications to
the theory of convex cocompactness in mapping class groups.\n
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kathryn Mann (Cornell University)
DTSTART;VALUE=DATE-TIME:20201104T200000Z
DTEND;VALUE=DATE-TIME:20201104T210000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/9
DESCRIPTION:Title: Stability for hyperbolic groups acting on their boundar
ies\nby Kathryn Mann (Cornell University) as part of McGill geometric grou
p theory seminar\n\nInteractive livestream: https://mcgill.zoom.us/j/98910
726246?pwd=VHlzTzdTZGtqcHVuWGNKdys4d0FzQT09\nPassword hint: Greek letter d
enoting Gromov hyperbolicity constant (5 letters)\n\nAbstract\nA hyperboli
c group acts naturally by homeomorphisms on its boundary. The theme of th
is talk is to say that\, in many cases\, such an action has very robust dy
namics. \n\nJonathan Bowden and I studied a very special case of this\, s
howing if G is the fundamental group of a compact\, negatively curved Riem
annian manifold\, then the action of G on its boundary is topologically st
able (small perturbations of it are semi-conjugate\, containing all the dy
namical information of the original action). In new work with Jason Mannin
g\, we get rid of the Riemannian geometry and show that such a result hold
s for hyperbolic groups with sphere boundary\, using purely large-scale ge
ometric techniques. \n\nThis theme of studying topological dynamics of bo
undary actions dates back at least as far as work of Sullivan in the 1980'
s\, although we take a very different approach. My talk will give some hi
story and some picture of the large-scale geometry involved in our work.\n
URL:https://mcgill.zoom.us/j/98910726246?pwd=VHlzTzdTZGtqcHVuWGNKdys4d0FzQ
T09
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zachary Munro (McGill University)
DTSTART;VALUE=DATE-TIME:20201111T200000Z
DTEND;VALUE=DATE-TIME:20201111T210000Z
DTSTAMP;VALUE=DATE-TIME:20201029T103143Z
UID:McGillGGT/10
DESCRIPTION:by Zachary Munro (McGill University) as part of McGill geometr
ic group theory seminar\n\nInteractive livestream: https://mcgill.zoom.us/
j/98910726246?pwd=VHlzTzdTZGtqcHVuWGNKdys4d0FzQT09\nPassword hint: Greek l
etter denoting Gromov hyperbolicity constant (5 letters)\nAbstract: TBA\n
URL:https://mcgill.zoom.us/j/98910726246?pwd=VHlzTzdTZGtqcHVuWGNKdys4d0FzQ
T09
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