BEGIN:VCALENDAR
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BEGIN:VEVENT
SUMMARY:Mikhail Ovcharenko (HSE)
DTSTART:20200416T150000Z
DTEND:20200416T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/1
DESCRIPTION:Title: Fano weighted complete intersections of large codimension\nb
y Mikhail Ovcharenko (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nLe
t $X$ be a smooth Fano variety. The index of $X$ is the largest natural nu
mber $i_X$ such that the canonical class $K_X$ is divisible by $i_X$ in th
e Picard group of $X$. It is well known that $i_X \\le n(X) + 1$ for $n(X)
= dim(X)$.\n\nWe are going to consider smooth Fano weighted complete inte
rsections over an algebraically closed field of characteristic zero. It is
known that\n$k(X) \\le n(X) + 1 - i_X$\nfor any such $X$\, where $k(X)$ i
s the codimension of $X$.\n\nLet us introduce new invariant $r(X) = n(X) -
k(X) - i_X + 1$.\nIn the talk I will outline what is known about smooth F
ano weighted complete intersection of given $r(X) = r_0$.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Joaquín Moraga (Princeton University)
DTSTART:20200422T150000Z
DTEND:20200422T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/2
DESCRIPTION:Title: The local fundamental group of klt singularities\nby Joaquí
n Moraga (Princeton University) as part of Iskovskikh seminar\n\n\nAbstrac
t\nWe will discuss some recent developments in the understanding of klt si
ngularities\,\nparticularly\, the Jordan property for the local fundamenta
l group. Then\, we will discuss how \na large local fundamental group refl
ects in the geometry of the singularity. The approach\nto this question gi
ves rise to some interesting conjectures about Fano type varieties with \n
large finite abelian automorphisms.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:John Ottem (University of Oslo)
DTSTART:20200430T150000Z
DTEND:20200430T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/3
DESCRIPTION:Title: Tropical degenerations and stable rationality\nby John Ottem
(University of Oslo) as part of Iskovskikh seminar\n\n\nAbstract\nI will
explain how tropical degenerations and birational specialization technique
s can be used in rationality problems. In particular\, I will show that ge
neric quartic fivefolds\, as well as many other complete intersections in
projective space\, are stably irrational. This is joint work with Johannes
Nicaise.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arman Sarikyan (Moscow State University)
DTSTART:20200504T150000Z
DTEND:20200504T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/4
DESCRIPTION:Title: On Stable conjugacy of Finite Subgroups of the Plane Cremona Gro
up\nby Arman Sarikyan (Moscow State University) as part of Iskovskikh
seminar\n\n\nAbstract\nI will speak about linearization and stable lineari
zation of finite subgroups of the plane Cremona group. We will discuss an
example of nonlinerizable but stably linerizable group. Then I will classi
fy all linearizable and nonlinerizable groups and in some cases we will pr
oof the nonexistence of stable linearization.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Olivier Benoist (CNRS)
DTSTART:20200507T150000Z
DTEND:20200507T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/5
DESCRIPTION:Title: Intermediate Jacobians and rationality over arbitrary fields
\nby Olivier Benoist (CNRS) as part of Iskovskikh seminar\n\n\nAbstract\nC
lemens and Griffiths have used intermediate Jacobians to show that smooth
cubic threefolds are irrational. In this talk\, I will explain how to exte
nd the Clemens-Griffiths method over arbitrary fields. As an application\,
I will show that a three-dimensional smooth complete intersection of two
quadrics over a field $\\mathbb k$ is $\\mathbb k$-rational if and only if
it contains a line defined over $\\mathbb k$. This is joint work with Oli
vier Wittenberg.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ignasi Mundet i Riera (University of Barselona)
DTSTART:20200514T150000Z
DTEND:20200514T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/6
DESCRIPTION:Title: Jordan and almost fixed point properties for topological manifol
ds\nby Ignasi Mundet i Riera (University of Barselona) as part of Isko
vskikh seminar\n\n\nAbstract\nI will explain recent results on the Jordan
property for homeomorphism\ngroups that generalize most of the presently k
nown results about Jordan\ndiffeomorphism groups. A crucial ingredient in
these results is a recent \ntheorem of Csikós\, Pyber and Szabó. I will
also talk about the following\napplication. Let X be a compact topological
manifold\, possibly with boundary\,\nwith nonzero Euler characteristic. T
hen there exists a constant $C$ such\nthat for any continuous action of an
y finite group $G$ on $X$ there is a point\nin $X$ whose stabilizer has in
dex in $G$ not bigger than $C$.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:John Lesieutre (The Pennsylvania State University)
DTSTART:20200521T150000Z
DTEND:20200521T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/7
DESCRIPTION:Title: Pathologies of the volume function\nby John Lesieutre (The P
ennsylvania State University) as part of Iskovskikh seminar\n\n\nAbstract\
nThe "volume" of a line bundle $L$ on a projective variety is a measure of
the growth rate of the number of sections of its tensor powers $L^{\\otim
es m}$. I will describe two examples in which the behavior of this functi
on near the pseudoeffective boundary has unexpectedly complicated behavior
\, and discuss some implications for attempts to define a numerical analog
of the Iitaka dimension.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Victor Batyrev (University of Tübingen)
DTSTART:20200528T150000Z
DTEND:20200528T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/8
DESCRIPTION:Title: Stringy Euler numbers of toric Calabi-Yau hypersurfaces\nby
Victor Batyrev (University of Tübingen) as part of Iskovskikh seminar\n\n
\nAbstract\nThe talk is devoted to stringy\ninvariants of singular algebra
ic varieties\nand their applications in birational geometry\nand mirror sy
mmetry. Projective Calabi-Yau\nmodels of non-degenerate affine hypersurfac
es in\nalgebraic torus provide simplest\nexamples of explicit combinatori
al formulas\nfor stringy invariants. I explain some recent\nresults and op
en questions motivated by different\nmirror symmetry constructions.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrey Trepalin (Steklov Mathematical Institute)
DTSTART:20200604T150000Z
DTEND:20200604T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/9
DESCRIPTION:Title: Birational permutations of projective plane (based on works of S
.Cantat and S.Asgarli\, K.Lai\, M.Nakahara and S.Zimmermann)\nby Andre
y Trepalin (Steklov Mathematical Institute) as part of Iskovskikh seminar\
n\n\nAbstract\nLet us consider a projective plane over a finite field K. I
f a birational transformation and its inverse are defined at each K-point\
, then this transformation defines a permutation of K-points. In the talk
we discuss for which fields we can realize any permutation\, and for which
not.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jean-Louis Colliot-Thélène (Université Paris-Saclay)
DTSTART:20200611T150000Z
DTEND:20200611T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/10
DESCRIPTION:Title: Zero-cycles on Del Pezzo surfaces\nby Jean-Louis Colliot-Th
élène (Université Paris-Saclay) as part of Iskovskikh seminar\n\n\nAbst
ract\nIn 1974\, D. Coray showed that on a smooth cubic surface with a clos
ed point\nof degree prime to 3 there exists such a point of degree 1\, 4 o
r 10.\nWe show how a combination of generization\, specialisation\,\nBert
ini theorems and large fields avoids considerations of special\ncases in h
is argument. For del Pezzo surfaces of degree 2\, we give\nan analogue of
Coray's result. For smooth cubic surfaces with a rational point\,\nwe sho
w that any zero-cycle of degree at least 10 is rationally equivalent to\na
n effective cycle. For smooth cubic surfaces without a rational point\,\n
we relate the question whether there exists a degree 3 point \nwhich is no
t on a line to the question whether rational points are dense\non a del Pe
zzo surface of degree 1.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yi Gu
DTSTART:20200618T073000Z
DTEND:20200618T090000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/11
DESCRIPTION:Title: Surface fibrations with large equivariant automorphism groups\nby Yi Gu as part of Iskovskikh seminar\n\n\nAbstract\nGiven a fibratio
n $f: X\\to C$ from a smooth projective surface $X$ to a smooth curve $C$
over an arbitrary algebraically closed field $k$. The equivariant automorp
hism group is $$\\mathbb{E}(X/C):=\\{\\\,\\\,(\\tau\,\\sigma) \\\,\\\,|\\\
,\\\, \\tau\\in \\mathrm{Aut}_k(X)\, \\sigma\\in \\mathrm{Aut}_k(C)\,\\\,\
\\,\\\, f\\circ \\tau =\\sigma\\circ f\\\,\\\, \\}$$\nwith natural composi
tion law.\n $$\n\\xymatrix{ X\\ar[rr]_\\sim^\\tau \\ar[d]_f&& X \\ar[d]^f
\\\\\nC \\ar[rr]_\\sim^\\sigma && C\n}\n$$\nThis group is an important inv
ariant of the fibration $f$ and sometimes that of the surface $X$. In this
talk\, we will give a classification of those relatively minimal surface
fibrations whose equivariant automorphism group $\\mathbb{E}(X/C)$ is infi
nite. As an application\, we will also discuss the Jordan property of the
automorphism group of a minimal surface of Kodaira dimension one.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Caucher Birkar (University of Cambridge)
DTSTART:20200625T130000Z
DTEND:20200625T143000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/12
DESCRIPTION:Title: On non-rationality of degenerations of del Pezzo surfaces\n
by Caucher Birkar (University of Cambridge) as part of Iskovskikh seminar\
n\n\nAbstract\nIt is well-known that a degeneration of a del Pezzo surface
may not be rational. A natural question is how far can it be from being r
ational. In this talk I will describe some recent results in this directio
n\, in joint work with Konstantin Loginov.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Brendan Hassett (Brown University)
DTSTART:20200702T150000Z
DTEND:20200702T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/13
DESCRIPTION:Title: Symbols\, birational geometry\, and computations\nby Brenda
n Hassett (Brown University) as part of Iskovskikh seminar\n\n\nAbstract\n
We are interested in $G$-birational equivalence of varieties where $G$ is
a \nfinite group. Kontsevich-Tschinkel and Kresch-Tschinkel have developed
\nsymbol formalism to construct invariants that show rich internal \nstru
cture. We present examples of their computation in a number of \nsituation
s.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Giovanni Mongardi (Bologna University)
DTSTART:20200709T150000Z
DTEND:20200709T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/14
DESCRIPTION:Title: IHS Manifolds: Automorphisms\, Kahler cones and related questio
ns\nby Giovanni Mongardi (Bologna University) as part of Iskovskikh se
minar\n\n\nAbstract\nAfter a (dramatically brief) introduction on IHS or H
yperkähler\nmanifolds\, we will\nsurvey several results on the shape of t
heir Kähler cones and related\ncones in the projective setting (ample\, m
ovable) and a\nBoucksom-Zarisky decomposition for divisors. Then\, we sket
ch how these\nproperties can be used to describe automorphisms of IHS mani
folds.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yuri Tschinkel (Courant Institute of Mathematical Sciences)
DTSTART:20200917T150000Z
DTEND:20200917T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/15
DESCRIPTION:Title: Equivariant birational types\nby Yuri Tschinkel (Courant In
stitute of Mathematical Sciences) as part of Iskovskikh seminar\n\n\nAbstr
act\nI will discuss new invariants in equivariant birational geometry (joi
nt with B. Hassett and A. Kresch).\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Muhammad Imran Qureshi (KFUPM)
DTSTART:20201015T150000Z
DTEND:20201015T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/16
DESCRIPTION:Title: Fano 4-folds in weighted Grassmannians\nby Muhammad Imran Q
ureshi (KFUPM) as part of Iskovskikh seminar\n\n\nAbstract\nA weighted fla
g variety is a weighted projective analog of the usual flag variety. In th
is talk\, I will provide an introduction and motivation behind the subject
of weighted flag varieties\, with particular emphasis on the first non-tr
ivial case of weighted Grassmannians. I aim to show that how one may use t
hem as ambient varieties to construct interesting classes of algebraic var
ieties (Fano\, Calabi-Yau\, etc)\, which are important from the point of v
iew of the classification of algebraic varieties. As an application\, I
will present some new deformation families of smooth Fano 4-folds of index
1.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Constantin Loginov (HSE)
DTSTART:20201029T150000Z
DTEND:20201029T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/17
DESCRIPTION:Title: Maximal log Fano pairs as generalized Bott towers\nby Const
antin Loginov (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nLog Fano
varieties are natural generalizations of Fano varieties. They\nare defined
as pairs $(X\, D)$ such that $-K_X-D$ is ample and $D$ is a\ndivisor call
ed a boundary. We consider the case of smooth projective X\nand reduced di
visor $D$ with simple normal crossings. Such pairs were\nstudied by H. Mae
da\, Takao and Kento Fujita\, and others. If in the\nabove definition we p
ut $D = 0$ then we recover the classical definition\nof a Fano variety. We
will study the opposite case of 'large enough'\nboundary divisor $D$. Mor
e precisely\, we will show that if $D$ has maximal\npossible number of com
ponents (such log Fano pairs we call maximal)\nthen the geometry of X\, in
cluding the Mori cone and extremal\ncontractions\, can be explicitly descr
ibed. It turns out that such\npairs $(X\, D)$ are toric and moreover\, $X$
admits the structure of a\ngeneralized Bott tower. This means that $X$ is
an iterated projective\nbundle over a point. If time permits\, we will di
scuss how maximal log\nFano pairs are related to semistable degenerations
of Fano varieties.\nThe talk is based on a joint work with J. Moraga.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Claudia Stadlmayr (Technische Universität München)
DTSTART:20201112T150000Z
DTEND:20201112T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/18
DESCRIPTION:Title: Which rational double points occur on del Pezzo surfaces?\n
by Claudia Stadlmayr (Technische Universität München) as part of Iskovsk
ikh seminar\n\n\nAbstract\nCanonical surface singularities\, also called r
ational double points (RDPs)\, can be classified according to their dual r
esolution graphs\, which are Dynkin diagrams of types A\, D\, and E. Where
as in characteristic different from 2\, 3\, and 5\, rational double points
are "taut"\, that is\, they are uniquely determined by their dual resolut
ion graph\, this is not necessarily the case in small characteristics. To
such non-taut RDPs Artin assigned a coindex distinguishing the ones with t
he same resolution graph in terms of their deformation theory.\n\nIn 1934\
, Du Val determined all configurations of rational double points that can
appear on complex RDP del Pezzo surfaces. In order to extend Du Vals work
to positive characteristic\, one has to determine the Artin coindices to d
istinguish the non-taut rational double points that occur.\n\nIn this talk
\, we will answer the question "Which rational double points (and configur
ations of them) occur on del Pezzo surfaces?" for all RDP del Pezzo surfac
es in all characteristics. This will be done by first reducing the problem
to RDP del Pezzo surfaces of degree 1 and then exploiting their connectio
n to (Weierstraß models of) rational (quasi-)elliptic surfaces.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Elana Kalashnikov (Harvard\, HSE)
DTSTART:20201126T150000Z
DTEND:20201126T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/19
DESCRIPTION:Title: Mirror symmetry and quiver flag varieties\nby Elana Kalashn
ikov (Harvard\, HSE) as part of Iskovskikh seminar\n\n\nAbstract\nQuiver f
lag varieties are a generalization of type A flag varieties\, first introd
uced by Alastair Craw. They are natural ambient spaces\, and play a specia
l role in the Fano classification program\, where mirror constructions for
these varieties are of particular interest. I'll survey some of the diffe
rent mirror constructions available for Grassmannians - via toric degenera
tions\, quantum cohomology\, and the Abelian/non-Abelian correspondence -
and discuss some of the work generalizing these constructions to quiver fl
ag varieties.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Roberto Svaldi (EPFL)
DTSTART:20201203T150000Z
DTEND:20201203T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/20
DESCRIPTION:Title: On the boundedness of Calabi--Yau elliptic fibrations\nby R
oberto Svaldi (EPFL) as part of Iskovskikh seminar\n\n\nAbstract\nOne of t
he main goals in Algebraic Geometry is to classify varieties.\nThe minimal
model program (MMP) is an ambitious program that aims to realize this goa
l\, from the point of view of birational geometry\, that is\, we are free
to modify the structure of a given variety along closed subsets to improve
its geometric features.\nAccording to the MMP\, there are 3 building bloc
ks in the birational classification of algebraic varieties: Fano varietie
s\, Calabi-Yau varieties\, and varieties of general type. One important q
uestion\, that is needed to further investigate the classification process
\, is whether or not varieties in these 3 classes have finitely many defor
mation types (a property called boundedness).\nOur understanding of the bo
undedness of Fano varieties and varieties of general type is quite solid
but Calabi-Yau varieties are still quite elusive. In this talk\, I will di
scuss recent results on the boundedness of elliptic Calabi-Yau varieties
\, which are the most relevant in physics.\nAs a consequence\, we obtain t
hat there are finitely many possibilities for the Hodge diamond of such ma
nifolds.\nThis is joint work with C. Birkar and G. Di Cerbo.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Evgeny Shinder (The University of Sheffield)
DTSTART:20201210T150000Z
DTEND:20201210T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/21
DESCRIPTION:Title: Two-dimensional birational geometry and factorization centers\nby Evgeny Shinder (The University of Sheffield) as part of Iskovskikh
seminar\n\n\nAbstract\nUsing results of Manin-Iskovskikh on classification
of geometrically rational surfaces over a perfect field\, and results of
Iskovskikh on classification of links between such surfaces\, I will expla
in the proof for uniqueness of factorization centers in dimension two. Exp
licitly\, the result is that the sequence of centers blown up and blown do
wn\, for any birational isomorphism $\\phi: X\\to Y$ is independent of $\\
phi$.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Höring (Université de Nice Sophia-Antipolis)
DTSTART:20210211T150000Z
DTEND:20210211T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/22
DESCRIPTION:Title: Fano manifolds with big tangent bundle that are covered by ``li
nes''\nby Andreas Höring (Université de Nice Sophia-Antipolis) as pa
rt of Iskovskikh seminar\n\n\nAbstract\nBy definition the anticanonical bu
ndle of a Fano manifold $X$ is ample\, but in general the tangent bundle $
T_X$ does not have any nice properties.\nIn fact\, recent examples obtaine
d in joint work with Jie Liu and Feng Shao indicate that the tangent bundl
e is almost never big. Unfortunately so far we do not have many tools to s
tudy this property in an abstract setting. In this talk I will speak about
work in progress with Jie Liu where we tackle the first case\, i.e. when
$T_X$ is big and $X$ admits a family of minimal rational curves of degree
two.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleksey Golota (HSE)
DTSTART:20210204T150000Z
DTEND:20210204T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/23
DESCRIPTION:Title: Filtrations\, admissible flags and delta-invariants\nby Ale
ksey Golota (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nDelta-invar
iant of a Fano variety is a numerical invariant characterizing uniform K-s
tability. This invariant is defined using log canonical thresholds of basi
s-type divisors. I am going to describe an «inductive» way to compute an
d estimate delta invariants for various examples of Fano varieties\, recen
tly proposed by Ahmadinezhad and Zhuang.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valery Lunts (University of Indiana)
DTSTART:20210218T150000Z
DTEND:20210218T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/24
DESCRIPTION:Title: Thick finitely generated subcategories on affine schemes and cu
rves\nby Valery Lunts (University of Indiana) as part of Iskovskikh se
minar\n\n\nAbstract\nI will report on three joint papers with Alexey Elagi
n.\nWe study thick subcategories of derived categories $D^b(cohX)$\,\nin c
ase $X$ is an affine scheme or a smooth projective curve. \nIn some cases
we obtain a complete classification. Also some\nsurprising phenomena occu
r.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jungkai A. Chen (National Taiwan University)
DTSTART:20210311T150000Z
DTEND:20210311T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/25
DESCRIPTION:Title: Threefolds of general type fibered by surfaces with small volum
e\nby Jungkai A. Chen (National Taiwan University) as part of Iskovski
kh seminar\n\n\nAbstract\nIn birational classification theory\, it is inte
resting to study the distribution and relations of birational invariants.
Also\, it is interesting to characterize those varieties with extremal inv
ariants. \nIn this talk\, we are going to work on threefolds of general ty
pe fibered by surfaces with small volume. \nBy combining the techniques of
geometry of linear systems and minimal model theory\, one can have quite
explicit description of such kinds of threefolds. \nWe will show applicati
ons to the study of Noether type inequality\, Severi type inequality and t
hreefolds with minimal volume.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleksey Golota (HSE)
DTSTART:20210318T150000Z
DTEND:20210318T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/26
DESCRIPTION:Title: Filtrations\, admissible flags and delta-invariants\nby Ale
ksey Golota (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nDelta-invar
iant of a Fano variety is a numerical invariant characterizing uniform K-s
tability. This invariant is defined using log canonical thresholds of basi
s-type divisors. I am going to describe an «inductive» way to compute an
d estimate delta invariants for various examples of Fano varieties\, recen
tly proposed by Ahmadinezhad and Zhuang.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrea Petracci (Freie Universität Berlin)
DTSTART:20210401T150000Z
DTEND:20210401T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/27
DESCRIPTION:Title: Toric geometry and singularities on K-moduli\nby Andrea Pet
racci (Freie Universität Berlin) as part of Iskovskikh seminar\n\n\nAbstr
act\nAn immediate consequence of Kodaira-Akizuki-Nakano vanishing is that
smooth Fano varieties have unobstructed deformations. The same holds for s
ingular Fano varieties with mild singularities and small dimension. In thi
s talk I will show how to use the combinatorics of lattice polytopes to co
nstruct examples of K-polystable toric Fano varieties with obstructed defo
rmations\, dimension at least 3\, and canonical singularities. This produc
es singularities (even reducible / non-reduced / non-Cohen-Macaulay) on K-
moduli stacks and K-moduli spaces of Fano varieties (which were recently c
onstructed using K-stability). This is joint work with Anne-Sophie Kaloghi
ros.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Weichung Chen (Steklov Mathematical Institute)
DTSTART:20210325T150000Z
DTEND:20210325T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/28
DESCRIPTION:Title: Bounded Complements for ϵ-lc generalized Fano Pairs\nby We
ichung Chen (Steklov Mathematical Institute) as part of Iskovskikh seminar
\n\n\nAbstract\nWe show the existence of strong $(\\epsilon\,n\,Γ)$-compl
ements for $\\epsilon$-lc generalized Fano pairs with coefficients of boun
daries in a fixed DCC set\, for any non-negative real number $\\epsilon$\,
given a certain ACC (ascending chain condition) for generalized $\\epsilo
n$-log canonical threshold. This is a generalization combining Filipazzi-M
oraga's result in 2018 and Han-Liu-Shokurov's result in 2019\, which are b
ased on Birkar's construction in 2016. This is a joint work with Y. Gongyo
and Y. Nakamura.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nikon Kurnosov (HSE\, UCL)
DTSTART:20210408T150000Z
DTEND:20210408T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/29
DESCRIPTION:Title: On Bogomolov theorem of classification of VII_0 surfaces\nb
y Nikon Kurnosov (HSE\, UCL) as part of Iskovskikh seminar\n\n\nAbstract\n
I will talk about the classification of VII_0 surfaces\, in particular abo
ut ideas of Bogomolov\, and Teleman's work\, who has made a complete class
ification. Time permits we will talk about bottlenecks of Bogomolov's appr
oach.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jingjun Han (John Hopkins University)
DTSTART:20210429T150000Z
DTEND:20210429T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/30
DESCRIPTION:Title: Shokurov's conjecture on conic bundles with canonical singulari
ties\nby Jingjun Han (John Hopkins University) as part of Iskovskikh s
eminar\n\n\nAbstract\nA conic bundle is a contraction $X\\to Z$ between no
rmal varieties of relative dimension $1$ such that the anit-canonical divi
sor is relatively ample. In this talk\, I will prove a conjecture of Shoku
rov which predicts that\, if $X\\to Z$ is a conic bundle such that $X$ has
canonical singularities\, then base variety $Z$ is always $\\frac{1}{2}$-
lc\, and the multiplicities of the fibers over codimension $1$ points are
bounded from above by $2$. Both values $\\frac{1}{2}$ and $2$ are sharp. T
his is a joint work with Chen Jiang and Yujie Luo.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantin Loginov (Steklov Mathematical Institute)
DTSTART:20210415T150000Z
DTEND:20210415T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/31
DESCRIPTION:Title: A finiteness theorem for elliptic Calabi-Yau threefolds\nby
Konstantin Loginov (Steklov Mathematical Institute) as part of Iskovskikh
seminar\n\n\nAbstract\nCalabi-Yau varieties are generalizations of ellipt
ic curves and K3\nsurfaces. From the point of view of algebraic geometry\,
the question\nof boundedness of such varieties seems interesting. Followi
ng the work\nof Mark Gross\, we prove that up to birational equivalence th
ere are\nonly finitely many families of 3-dimensional Calabi-Yau varieties
that\nsatisfy certain conditions. More precisely\, singularities should b
e\nterminal and factorial\, and the given variety should admit a fibration
\ninto elliptic curves over a rational surface.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sergey Rybakov (IITP)
DTSTART:20210422T140000Z
DTEND:20210422T153000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/32
DESCRIPTION:Title: Algebraic varieties over function fields and good towers of cur
ves over finite fields\nby Sergey Rybakov (IITP) as part of Iskovskikh
seminar\n\n\nAbstract\nGiven a smooth algebraic variety over a function f
ield we can construct a tower of algebraic curves (or\, equivalently\, a t
ower of function fields). We say that the tower is good if the limit of th
e number of points on a curve divided by genus is positive. For example\,
the generic fiber of the Legendre family of elliptic curves gives a good (
and optimal) tower over $F_{p^2}$. I will speak on good towers coming from
K3 surfaces.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikhail Ovcharenko (HSE)
DTSTART:20210527T150000Z
DTEND:20210527T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/33
DESCRIPTION:Title: On Dolgachev--Nikulin Duality for Fibers of Landau--Ginzburg Mo
dels of Smooth Fano Threefolds\nby Mikhail Ovcharenko (HSE) as part of
Iskovskikh seminar\n\n\nAbstract\nMirror Symmetry corresponds to Fano var
ieties certain one-dimensional families which are called Landau--Ginzburg
models. Elements of these families are expected to be Calabi--Yau varietie
s mirror dual to anticanonical sections of Fano varieties. In the three-di
mensional case one of the forms of Mirror Symmetry conjecture is provided
by Dolgachev--Nikulin duality of K3 surfaces. This conjecture was proved b
y Ilten--Lewis--Przyjalkowski in the case of Picard rank 1. In the talk we
will discuss the obtained results for Picard rank 2.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexandra Kuznetsova (HSE\, Ecole Polytechique)
DTSTART:20210916T150000Z
DTEND:20210916T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/34
DESCRIPTION:Title: Semi-continuity of dynamical degrees\nby Alexandra Kuznetso
va (HSE\, Ecole Polytechique) as part of Iskovskikh seminar\n\n\nAbstract\
nTo any birational automorphism we can associate its dynamical degree. Thi
s is a number characterising the growth of any ample class under iteration
of the automorphism. If the automorphism is regular\, then its dynamical
degree equals the absolute value of the greatest eigenvalue of the action
of the inverse image on the Neron-Severi group of the variety.\nIf we fix
a family of birational automorphisms\, then the dynamical degree defines
a function on the base of the family. I am going to tell the proof of Xie
Junyi's theorem that in the case of a family of surface birational automor
phisms this function is lower semi-continuous.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Litt (University of Georgia)
DTSTART:20210923T150000Z
DTEND:20210923T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/35
DESCRIPTION:Title: Arithmetic representations and non-commutative Siegel lineariza
tion\nby Daniel Litt (University of Georgia) as part of Iskovskikh sem
inar\n\n\nAbstract\nI'll explain joint work with Borys Kadets\, explaining
how to prove the following theorem. Let $X$ be a curve over a finitely ge
nerated field $k$\, and let $\\ell$ be a prime different from the characte
ristic of $k$. Then there exists $N=N(X\,\\ell)$ such that any semisimple
arithmetic representation of $\\pi_1(X_{\\bar k})$ into $GL_n(\\overline{\
\mathbb{Z}_\\ell})$\, which is trivial mod $\\ell^N$\, is in fact trivial.
This extends previous work of mine from characteristic zero to all charac
teristics. The main new idea is to introduce techniques from dynamics\; in
particular a non-commutative version of Siegel's linearization theorem. F
or example\, this gives restrictions on the possible torsion subgroups of
abelian varieties over function fields. I'll also explain some related joi
nt work in progress with Eric Katz on $\\ell$-adic analogues of non-Abelia
n Hodge theory.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Natalia Daurtseva (https://research.nsu.ru/en/persons/ndaurtseva)
DTSTART:20210930T150000Z
DTEND:20210930T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/36
DESCRIPTION:Title: On almost Hermitian structures on 6-dimensional manifolds\n
by Natalia Daurtseva (https://research.nsu.ru/en/persons/ndaurtseva) as pa
rt of Iskovskikh seminar\n\n\nAbstract\nSix-dimensional case is special in
geometry of almost Hermitian manifolds.\nThis is due to the existence of
a well-known Hopf problem on a 6-sphere\,\nthe properties of nearly Kaehle
r manifolds\, and a number of other reasons.\nI’ll talk about some quest
ions and progresses in almost Hermitian geometry\,\nin particular\, about
the properties of almost Hermitian structures of cohomogeneity 1 on a 6-sp
here.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Annalisa Grossi (https://annalisagrossi92.wixsite.com/home)
DTSTART:20211007T150000Z
DTEND:20211007T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/37
DESCRIPTION:Title: Induced nonsymplectic automorphisms on manifolds of OG6 type\nby Annalisa Grossi (https://annalisagrossi92.wixsite.com/home) as part
of Iskovskikh seminar\n\n\nAbstract\nIn 2000 O'Grady introduced a new exam
ple of hyperkaehler manifolds\nin dimension six as the symplectic resoluti
on of a certain fiber of a moduli space\nof sheaves on an abelian surface.
In this talk we give you a criterion to determine\nwhen a birational tran
sformation of an O'Grady six type manifold is induced by\nan automorphism
of the abelian surface. Using the lattice theoretic classi\ncation\nof non
symplectic automorphisms of O'Grady's sixfolds we give an application of\n
this criterion to detect when an automorphism is induced.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anastasia Vikulova (https://www.hse.ru/org/persons/401585497)
DTSTART:20211014T150000Z
DTEND:20211014T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/38
DESCRIPTION:Title: Enriques varieties\nby Anastasia Vikulova (https://www.hse.
ru/org/persons/401585497) as part of Iskovskikh seminar\n\n\nAbstract\nIn
this talk we will discuss generalizations of Enriques surfaces (so called
Enriques varieties) and construct all examples of such varieties\, which a
re known today.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anna Bot (University of Basel)
DTSTART:20211111T150000Z
DTEND:20211111T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/40
DESCRIPTION:Title: A smooth complex rational affine surface with uncountably many
nonisomorphic real forms\nby Anna Bot (University of Basel) as part of
Iskovskikh seminar\n\n\nAbstract\nA real form of a complex algebraic vari
ety $X$ is a real algebraic variety whose complexification is isomorphic t
o $X$. Up until recently\, it was known that many families of complex vari
eties have a finite number of nonisomorphic real forms. In 2019\, Lesieutr
e constructed an example of a projective variety of dimension six with inf
initely many\, and now\, Dinh\, Oguiso and Yu found a projective rational
surface with infinitely many as well. In this talk\, I’ll present the fi
rst example of a rational affine surface having uncountably many nonisomor
phic real forms. The first example with infinitely countably many real for
ms on an affine rational variety is due to Dubouloz\, Freudenberg and Mose
r-Jauslin.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexey Tuzhilin (MSU)
DTSTART:20211125T150000Z
DTEND:20211125T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/41
DESCRIPTION:Title: Symmetries of Gromov-Hausdorff Distance\nby Alexey Tuzhilin
(MSU) as part of Iskovskikh seminar\n\n\nAbstract\nThe famous Gromov-Haus
dorff distance measures the similarity degree of metric spaces. Since it b
oth satisfies the triangle inequality and vanishes for isometric spaces\,
it induces correctly a correspondent distance on isometry classes of metri
c spaces. The collection of all such classes form a proper class in terms
of Von Neumann–Bernays–Gödel set theory. We call such proper class by
Gromov-Hausdorff class and denote it as GH. The main question for the tal
k is to discuss what are the isometric mappings (local and global) of GH.
One of the most investigated part of GH is the Gromov-Hausdorff space M co
nsisting of all non-empty compact metric spaces (considered up to isometry
).\n\nWe start with a sketch of Ivanov-Tuzhilin's correction of the "Georg
e Lowther" proof (perhaps "George Lowther" is a pseudonym) that the isomet
ry group of M is trivial. Then we discuss some local isometries of M: it t
urns out that there are a lot of them. At last\, we formulate some conject
ures concerning the whole Gromov-Hausdorff class GH.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Artem Avilov (HSE)
DTSTART:20211021T150000Z
DTEND:20211021T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/42
DESCRIPTION:Title: G-birationally rigid del Pezzo varieties of degree 2\nby Ar
tem Avilov (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nIn this talk
we will classify nodal non-$\\mathbb Q$-factorial quartic double solids w
ith big enough automorphism group such that there are no simple equivarian
t links with another Mori fibrations.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexei Piskunov (HSE)
DTSTART:20211027T140000Z
DTEND:20211027T153000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/43
DESCRIPTION:Title: Symmetric powers of Severi-Brauer varieties\nby Alexei Pisk
unov (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nA Severi-Brauer va
riety over a field $k$ is an algebraic variety $X/k$ that becomes isomorph
ic to the projective space $\\mathbb P^n$ after the base change to a separ
able closure $k^{sep}$. I will show that $(n+1)$-th symmetric power of any
$n$-dimensional Severi-Brauer varietiy is rational. We will also study so
me facts about their arbitrary symmetric powers and Grassmanians. The talk
is due to the article of János Kollár and is going to be elementary (on
ly some basic facts from algebraic geometry will be used).\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantin Loginov (Steklov Mathematical Institute)
DTSTART:20211118T150000Z
DTEND:20211118T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/44
DESCRIPTION:Title: Termination of flips and fundamental groups (after Joaquín Mor
aga)\nby Konstantin Loginov (Steklov Mathematical Institute) as part o
f Iskovskikh seminar\n\n\nAbstract\nWe will talk about the connection betw
een topology of singularities of\nalgebraic varieties and the following im
portant conjectures in the\nminimal model program: termination of flips co
njecture and the\nconjecture on boundedness of minimal log discrepancies.
In\nparticular\, we will formulate the boundedness conjecture for the\nre
gional fundamental group\, which is proven by Joaquín for some\nclasses o
f singularities. Also\, we will show that this conjecture\nimplies termina
tion of flips for klt pairs in dimension 4.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/44/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikhail Ovcharenko (Steklov Mathematical Institute)
DTSTART:20211202T150000Z
DTEND:20211202T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/45
DESCRIPTION:Title: Varieties of general type with the smallest known volume (after
Esser--Totaro--Wang)\nby Mikhail Ovcharenko (Steklov Mathematical Ins
titute) as part of Iskovskikh seminar\n\n\nAbstract\nIn the talk we will c
onstruct smooth projective varieties of general type with the smallest kno
wn volume and others with the most known vanishing plurigenera.\n\nThe opt
imal volume bound is expected to decay doubly exponentially with dimension
. The constructed examples will have the required asymptotic.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/45/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ronald van Luijk (Universiteit Leiden)
DTSTART:20211209T150000Z
DTEND:20211209T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/46
DESCRIPTION:Title: Density of rational points on a family of Del Pezzo surfaces of
degree 1\nby Ronald van Luijk (Universiteit Leiden) as part of Iskovs
kikh seminar\n\n\nAbstract\nDel Pezzo surfaces are geometrically among the
easiest surfaces. They have a degree between 1 and 9\, and the lower the
degree\, the more complicated the surface. Those of degree 3 are the famou
s cubic surfaces containing 27 lines. The arithmetic of Del Pezzo surfaces
\, however\, is much less understood. It is conjectured that on every Del
Pezzo surface over a number field k with at least one k-rational point\, t
he set of k-rational points is automatically dense. This has been proved f
or all Del Pezzo surfaces of degree at least 3\, most of degree 2\, but on
ly few of degree 1\, which is the case we will discuss. These surfaces hav
e a natural elliptic fibration. We will prove for a large family of these
surfaces that the set of rational points is Zariski dense if and only if t
here is at least one fiber (satisfying very mild conditions) that contains
infinitely many rational points. This is joint work with Wim Nijgh\, base
d on work of Rosa Winter and Julie Desjardins.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/46/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Julia Schneider (University of Tolouse)
DTSTART:20220127T150000Z
DTEND:20220127T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/47
DESCRIPTION:Title: Generating the plane Cremona group by involutions\nby Julia
Schneider (University of Tolouse) as part of Iskovskikh seminar\n\n\nAbst
ract\nI will discuss the following theorem: For any perfect field\, the pl
ane Cremona group is generated by involutions. I will explain how the deco
mposition of birational maps into Sarkisov links gives a generating set of
the plane Cremona group. Then I will decompose these generators into invo
lutions\, among them are Geiser and Bertini involutions as well as reflec
tions in an orthogonal group associated to a quadratic form. This is joint
work with Stéphane Lamy.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/47/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anastasia Vikulova (HSE)
DTSTART:20220203T150000Z
DTEND:20220203T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/48
DESCRIPTION:Title: The Looijenga-Lunts-Verbitsky algebra\nby Anastasia Vikulov
a (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nIn this talk we will
discuss the Looijenga-Lunts-Verbitsky algebra of compact hyperkahler manif
olds. We study its properties and its action on the ring of rational cohom
ologies.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/48/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Joaquin Moraga (Princeton University)
DTSTART:20220210T150000Z
DTEND:20220210T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/49
DESCRIPTION:Title: Reductive quotient singularities\nby Joaquin Moraga (Prince
ton University) as part of Iskovskikh seminar\n\n\nAbstract\nThe study of
quotients by reductive groups is an important topic in algebraic geometry.
\nIt manifests when studying moduli spaces\, orbit spaces\, and $G$-variet
ies. \nMany important classes of singularities\, as rational singularities
\, are preserved under quotients by reductive groups.\nIn this talk\, we w
ill show that the singularities of the MMP are preserved under reductive q
uotients. \nAs an application\, we show that many good moduli spaces\, \na
s the moduli of smoothable $K$-polystable varieties\, have klt type singul
arities.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/49/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrey Trepalin (Steklov Mathematical Institute)
DTSTART:20220217T150000Z
DTEND:20220217T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/50
DESCRIPTION:Title: Birational classification of pointless del Pezzo surfaces of de
gree 8\nby Andrey Trepalin (Steklov Mathematical Institute) as part of
Iskovskikh seminar\n\n\nAbstract\nLet $k$ be an algebraically nonclosed f
ield of characteristic $0$. We show that two pointless quadric surfaces ov
er $k$\nare birationally equivalent if and only if they are isomorphic. Al
so we describe minimal surfaces birationally\nequivalent to a given pointl
ess quadric surface.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/50/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikhail Ovcharenko (Steklov Mathematical Institute)
DTSTART:20220224T150000Z
DTEND:20220224T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/51
DESCRIPTION:Title: Boundness of log-canonical surfaces of general type (after Alex
eev-Mori)\nby Mikhail Ovcharenko (Steklov Mathematical Institute) as p
art of Iskovskikh seminar\n\n\nAbstract\nIn the talk we discuss the proof
of the theorem of Alexeev-Mori on the existence of a lower bound on the se
lf-intersection of a log-canonical divisor of a log-canonical surface of g
eneral type. More precisely\, the bound is given in the terms of an (arbit
rary) subset of $\\mathbb R$ containing the coefficients of the boundary a
nd satisfying the descending chain condition.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/51/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ivan Cheltsov (University of Edinburgh)
DTSTART:20220317T150000Z
DTEND:20220317T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/52
DESCRIPTION:Title: Equivariant birational geometry of (three-dimensional) projecti
ve space\nby Ivan Cheltsov (University of Edinburgh) as part of Iskovs
kikh seminar\n\n\nAbstract\nWe will describe $G$-equivariant birational ge
ometry of (three-dimensional) projective space \nin the case when the grou
p $G$ does not fix a point and does not leave a pair of skew lines invaria
nt. This is a joint project with Arman Sarikyan and Igor Krylov.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/52/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexey Golota (HSE)
DTSTART:20220324T150000Z
DTEND:20220324T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/53
DESCRIPTION:Title: On families of birational involutions of projective space and C
remona group\nby Alexey Golota (HSE) as part of Iskovskikh seminar\n\n
\nAbstract\nFollowing a paper by S. Zikas\, I will present an explicit con
struction\, which allows to prove that the group of birational automorphis
ms of three-dimensional projective space over the field of complex numbers
is not simple.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/53/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexei Piskunov (HSE)
DTSTART:20220331T150000Z
DTEND:20220331T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/54
DESCRIPTION:Title: Rationality criteria for motivic zeta-function\nby Alexei P
iskunov (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nIt is known tha
t for a smooth projective geometrically-connected curve motivic zeta-funct
ion is rational. In general it is not true - even the case of smooth proje
ctive complex surfaces provides a counterexample. I will prove a criteria
for motivic zeta-function of complex surfaces to be rational following an
article by M.Larsen and V.Lunts.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/54/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marc Abboud
DTSTART:20220407T150000Z
DTEND:20220407T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/55
DESCRIPTION:Title: Actions of nilpotent groups on complex algebraic varieties\
nby Marc Abboud as part of Iskovskikh seminar\n\n\nAbstract\nWe study nilp
otent groups that act faithfully on complex algebraic varieties. For finit
e groups\, we show that any finite p-subgroup of polynomial automorphisms
of $k^d$ is isomorphic to a subgroup of $GL_d (k)$ when $k$ is finitely ge
nerated over the field of rational numbers\, this gives an explicit bound
on the size of such groups using a theorem of Minkowski and Schur. For fin
itely generated nilpotent groups acting on a complex varieties\, we show t
hat we can find constraints on the dimension of the varieties using tools
from $p$-adic analysis and $p$-adic Lie groups. In this talk\, I will disc
uss the proofs of these two results which both rely on a method of base ch
ange.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/55/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexey Talambutsa (Steklov Mathematical Institute)
DTSTART:20220414T150000Z
DTEND:20220414T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/56
DESCRIPTION:Title: On the growth functions of finitely generated groups\nby Al
exey Talambutsa (Steklov Mathematical Institute) as part of Iskovskikh sem
inar\n\n\nAbstract\nFor a group $G$ generated by some finite set $S$\, the
growth function $f_{G\,S}(n)$ is defined as the number of distinct elemen
ts of the group that can be written as a product $a_1 a_2 \\ldots a_n$\, w
here $a_i\\in S\\cup S^{-1}\\cup \\{1\\}$. In other words\, this function
is equal to the number of vertices in the ball of radius $n$ in the Cayley
graph $Cay(G\,S)$. Over the past 50 years\, a number of results have been
obtained in this area\, including the famous theorem by M. Gromov's on th
e structure of groups having polynomial growth and examples of groups havi
ng intermediate growth constructed by R.I.Grigorchuk. I will review these
and some other interesting results about growth functions and also describ
e the connection of growth functions of Coxeter groups to finite automata\
, Perron-Frobenius theory and Pisot and Salem algebraic numbers.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/56/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vladimir Shein (HSE)
DTSTART:20220421T150000Z
DTEND:20220421T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/57
DESCRIPTION:Title: The rationality of motivic zeta functions of curves with no rat
ional points\nby Vladimir Shein (HSE) as part of Iskovskikh seminar\n\
n\nAbstract\nIn this talk we will show that the motivic zeta function of a
ny geometrically irreducible curve is a rational function. The talk will b
e based on the article of the same name by D. Litt\, who proved the tricki
est part of the statement (when the curve has no rational points).\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/57/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Raisa Serova (MSU)
DTSTART:20220428T150000Z
DTEND:20220428T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/58
DESCRIPTION:Title: Small maximal spaces of degenerate matrices\nby Raisa Serov
a (MSU) as part of Iskovskikh seminar\n\n\nAbstract\nIn 1985 Fillmore\, La
urie and Radjavi asked whether a maximal linear subspace in the variety of
degenerate $N \\times N$-matrices can have dimension smaller than $N$. Fo
llowing the work of J.Draisma\, \nwe will show that for infinitely many $
N$ there exists an 8-dimensional maximal space in the variety of degenerat
e $N \\times N$-matrices.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/58/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pavel Shteyner (MSU)
DTSTART:20220505T150000Z
DTEND:20220505T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/59
DESCRIPTION:Title: Matrix majorizations and their endomorphisms\nby Pavel Shte
yner (MSU) as part of Iskovskikh seminar\n\n\nAbstract\nVector and matrix
majorizations are a wide class of important relations on linear spaces and
algebras. This theory dates back to Muirhead 1903 and Lorenz 1905. It was
later developed by Hardy\, Littlewood and Polya. Modern theory of majoriz
ation has many applications in various branches of mathematics\, economics
and many other areas. At the same time\, this theory contains many import
ant algebraic questions. We investigate various majorization relations of
matrices and matrix families and their geometric and combinatorial charact
erizations. In addition\, we provide characterizations of linear operators
preserving or converting majorizations.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/59/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikhail Troshkin (HSE)
DTSTART:20220908T150000Z
DTEND:20220908T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/60
DESCRIPTION:Title: Bertini theorems over finite fields\nby Mikhail Troshkin (H
SE) as part of Iskovskikh seminar\n\n\nAbstract\nClassical Bertini theorem
s state that if a projective variety is smooth or irreducible\, its inters
ection with a generic hypersurface has the same property. When a given var
iety is defined over a finite field\, we can count the fraction of hypersu
rfaces that intersect it in such way. I am going to discuss the asymptotic
s of the number of smooth sections by hypersurfaces as the degree of hyper
surface tends to infinity.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/60/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mikhail Ovcharenko (Steklov Mathematical Institute)
DTSTART:20220915T150000Z
DTEND:20220915T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/61
DESCRIPTION:Title: The Lefschetz defect of a smooth Fano veriety (after C. Casagra
nde)\nby Mikhail Ovcharenko (Steklov Mathematical Institute) as part o
f Iskovskikh seminar\n\n\nAbstract\nThe Lefschetz defect is an invariant o
f a smooth complex Fano variety $X$ introduced by C. Casagrande. Informall
y\, it measures the failure of Lefschetz hyperplane theorem for non-ample
prime divisors on $X$. The main property of the Lefschetz defect is that i
n a certain sense the classification by the Lefschetz defect generalizes t
he classification of smooth del Pezzo surfaces. Using the Lefschetz defect
\, it is possible to recover the Mori--Mukai classification of smooth Fano
3-folds of Picard number $\\rho(X)>4$.\n\nIn the talk we will discuss the
connection of the Lefschetz defect with birational geometry\, and its app
lications to the classification of smooth Fano 4-folds.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/61/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexandra Kuznetsova (Steklov Mathematical Institute)
DTSTART:20220922T150000Z
DTEND:20220922T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/62
DESCRIPTION:Title: The ordinal of dynamical degrees\nby Alexandra Kuznetsova (
Steklov Mathematical Institute) as part of Iskovskikh seminar\n\n\nAbstrac
t\nThe birational automorphism $f$ of a smooth surface acts on the Neron-S
everi \ngroup of the surface as a linear operator $f^*$. The iterates $(f^
n)^*$ grows \nexponentially i.e. as $\\lambda^n$. The base $\\lambda$ is c
alled the dynamical \ndegree of $f$. It is a positive real number. Moreove
r\, if we fix a surface then \nthe set of all dynamical degrees of its aut
omorphisms is well-ordered. In my \ntalk I am going to describe the ordina
l of this set. The talk is based on the \npaper ``The ordinal of dynamical
degrees of birational maps of the projective \nplane'' by Anna Bot.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/62/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Egor Yaskinsky (Institut Polytechnique de Paris)
DTSTART:20221013T150000Z
DTEND:20221013T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/63
DESCRIPTION:Title: Birational automorphisms of Severi-Brauer surfaces and the Crem
ona group\nby Egor Yaskinsky (Institut Polytechnique de Paris) as part
of Iskovskikh seminar\n\n\nAbstract\nA Severi-Brauer surface over a field
$k$ is an algebraic $k$-surface which is isomorphic to the projective pla
ne over the algebraic closure of $k$. I will describe the group of biratio
nal transformations of a non-trivial Severi-Brauer surface\, proving in pa
rticular that "in most cases" it is not generated by elements of finite or
der. This is already a very curious feature\, since the group of birationa
l self-maps of a trivial Severi-Brauer surface\, i.e. of a projective plan
e\, is always generated by involutions (at least over a perfect field). Th
en I will demonstrate how to use this result to get some insights into the
structure of the groups of birational transformations of some higher-dime
nsional varieties\, including the projective space of dimension $> 3$.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/63/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexander Zaitsev (HSE)
DTSTART:20221027T150000Z
DTEND:20221027T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/64
DESCRIPTION:Title: Birational transformations of projective plane\nby Alexande
r Zaitsev (HSE) as part of Iskovskikh seminar\n\n\nAbstract\nOver non-alge
braically closed field $k$ there are birational automorphisms\, which are
regular at every $k$-point. These automorphisms form a subgroup of the Cre
mona group\, and each such automorphism induce a permutation of points of
projective space. Following a paper by Asgarli\, Lai\, Nakahara and Zimmer
mann\, I will show\, which permutations of points of projective plane over
finite field can be obtained via these birational automorphisms. \n\nMore
precisely\, I will prove\, that each permutation of points of projective
plane over fields of odd characteristic and over field of two elements can
be obtained from birational automorphism\, which is regular at every rati
onal point.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/64/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ivan Polekhin (Steklov Mathematical Institute)
DTSTART:20221117T150000Z
DTEND:20221117T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/65
DESCRIPTION:Title: Some problems on the inverted pendulum dynamics\nby Ivan Po
lekhin (Steklov Mathematical Institute) as part of Iskovskikh seminar\n\n\
nAbstract\nLet us consider the motion of a planar (inverted) pendulum in t
he\npresence of a horizontal force\, which is not assumed to be bounded\n(
its magnitude can be arbitrarily large as time tends to infinity). Is\nit
true that\, for any such force\, there exists an initial position of\nthe
pendulum such that\, being released with zero initial velocity from\nthis
position\, the pendulum never falls? If this external force is\nperiodic\,
is it true that there exists a periodic non-falling\nsolution? Do similar
statements hold for a spherical inverted\npendulum? We will answer these
and a number of other questions in our\ntalk.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/65/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vasilij Rozhdestvenskij (HSE)
DTSTART:20221124T150000Z
DTEND:20221124T163000Z
DTSTAMP:20260404T095501Z
UID:Iskovskikh/66
DESCRIPTION:Title: Topology of real algebraic sets\nby Vasilij Rozhdestvenskij
(HSE) as part of Iskovskikh seminar\n\n\nAbstract\nA real algebraic set i
s a set of common zeros of a system of polynomials with real coefficients.
The main subject of the talk will be a Nach theorem. The Nash theorem sta
tes that if $M$ is a smooth closed manifold embedded into $\\mathbb R^N$ t
hen there exists a diffeomorphism $f: \\mathbb R^N \\to \\mathbb R^N$ such
that the image $f(M)$ is a connected component of a real algebraic set (p
rovided that $N$ is sufficiently large). Also it will be explained that on
e can actually choose $f$ such that $f(M)$ will be just a real algebraic s
et. As an easy corollary we get that every smooth closed manifold is diffe
omorphic to a real algebraic set.\n
LOCATION:https://stable.researchseminars.org/talk/Iskovskikh/66/
END:VEVENT
END:VCALENDAR