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BEGIN:VEVENT
SUMMARY:Andrea Seppi (Université de Grenoble)
DTSTART:20200415T120000Z
DTEND:20200415T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/1
DESCRIPTION:Title: Examples of four-dimensional geometric transition\nby Andrea Seppi (
Université de Grenoble) as part of Sapienza A&G Seminar\n\n\nAbstract\nRo
ughly speaking\, a geometric transition is a deformation of geometric stru
ctures on a manifold\, by “transitioning” between different geometries
. Danciger introduced a new such transition\, which enables to deform from
hyperbolic structures to Anti-de Sitter structure\, going through another
type of real projective structures called “half-pipe”\, and provided
conditions for a compact 3-manifold to admit a geometric transition of thi
s type. By extending a construction of Kerckhoff and Storm\, I will descri
be examples of finite-volume geometric transition in dimension 4.\n\nThis
is joint work with Stefano Riolo.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ralf Köhl (Universität Giessen)
DTSTART:20200422T120000Z
DTEND:20200422T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/2
DESCRIPTION:Title: The geometry of Kac-Moody groups\nby Ralf Köhl (Universität Giesse
n) as part of Sapienza A&G Seminar\n\n\nAbstract\nKac-Moody groups enjoy v
ery many nice geometric properties \nvia their action on twin buildings\,
on generalized flag manifolds\, and \non highest-weight modules endowed wi
th an anisotropic form.\n\nIn this talk I want to topological Kac-Moody gr
oups by comparing their \nproperties to semisimple Lie groups. I will intr
oduce symmetric spaces \nfor Kac-Moody groups\, I will compute the fundame
ntal group of \ntopological Kac-Moody groups\, and I will give evidence fo
r Kostant \nconvexity.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Laura Pertusi (Università statale di Milano)
DTSTART:20200429T120000Z
DTEND:20200429T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/3
DESCRIPTION:Title: Stability conditions and moduli spaces for Kuznetsov components of Gushe
l-Mukai varieties\nby Laura Pertusi (Università statale di Milano) as
part of Sapienza A&G Seminar\n\n\nAbstract\nA generic Gushel-Mukai variet
y X is a quadric section of a linear section of the Grassmannian Gr(2\,5).
Kuznetsov and Perry proved that the bounded derived category of X has a s
emiorthogonal decomposition with exceptional objects and a non-trivial sub
category Ku(X)\, known as the Kuznetsov component. In this talk we will di
scuss the construction of stability conditions on Ku(X) and\, consequently
\, on the bounded derived category of X. As applications\, for X of even-d
imension\, we will construct locally complete families of hyperkaehler man
ifolds from moduli spaces of stable objects in Ku(X) and we will determine
when X has a homological associated K3 surface.\n\nThis is a joint work w
ith Alex Perry and Xiaolei Zhao.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexander Lytchak (Universität Köln)
DTSTART:20200520T120000Z
DTEND:20200520T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/4
DESCRIPTION:Title: Structure of non-positively curved spaces\nby Alexander Lytchak (Uni
versität Köln) as part of Sapienza A&G Seminar\n\n\nAbstract\nIn the tal
k I would like to discuss local geometric\, analytic and topological struc
ture of spaces with upper curvature bounds and extendible geodesics.\nThe
talk will be based on joint work with Koichi Nagano.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Michele D’Adderio (Université libre de Bruxelles)
DTSTART:20200527T120000Z
DTEND:20200527T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/5
DESCRIPTION:Title: Partial and global representations of finite groups\nby Michele D’
Adderio (Université libre de Bruxelles) as part of Sapienza A&G Seminar\n
\n\nAbstract\nThe notions of partial actions and partial representations h
ave been extensively studied in several algebraic contexts in the last 25
years.\nIn this talk we introduce these concepts and give a short overview
of the results known for finite groups. We will briefly show how this the
ory extends naturally the classical global theory\, in particular in the i
mportant case of the symmetric group.\nThis is joint work with William Hau
tekiet\, Paolo Saracco and Joost Vercruysse.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Boggi (UFMG Belo Horizonte)
DTSTART:20200506T120000Z
DTEND:20200506T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/6
DESCRIPTION:Title: Automorphisms of procongruence mapping class groups\nby Marco Boggi
(UFMG Belo Horizonte) as part of Sapienza A&G Seminar\n\n\nAbstract\nIn th
is talk\, I will discuss the automorphism group of the procongruence mappi
ng class group and of the associated procongruence curve and pants complex
es. In analogy with a classical result of Ivanov for mapping class groups\
, this allows to determine the group of automorphisms of the $arithmetic$
procongruence mapping class group which satisfy a natural geometric condit
ion. It is a nontrivial fact that this condition holds in genus $0$. Let $
\\mathcal{M}_{0\,n}$ be the moduli space of $n$-labeled\, genus $0$ algebr
aic curves. It follows\, in particular\, that $\\mathrm{Out}(\\pi_1^\\math
rm{et}(\\mathcal{M}_{0\,n}\\otimes\\Q))\\cong\\Sigma_n$ for $n\\geq 5.\\ne
wline$\nThis talk is based on a joint work with Louis Funar and Pierre Loc
hak (cf. $\\texttt{arXiv:2004.04135}$).\n
LOCATION:https://researchseminars.org/talk/AGSeminar/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cristiano Spotti (Aarhus Universitet)
DTSTART:20200603T120000Z
DTEND:20200603T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/7
DESCRIPTION:Title: On log Kähler-Einstein metrics\nby Cristiano Spotti (Aarhus Univers
itet) as part of Sapienza A&G Seminar\n\n\nAbstract\nIn this talk I will d
iscuss examples and some geometric properties of KE metrics with cone angl
e singularities along possibly singular (in general worse than normal cros
sing) divisors.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Karen Vogtmann (University of Warwick)
DTSTART:20200617T120000Z
DTEND:20200617T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/8
DESCRIPTION:Title: Outer space for RAAGs\nby Karen Vogtmann (University of Warwick) as
part of Sapienza A&G Seminar\n\n\nAbstract\nIn recent years right-angled A
rtin groups (RAAGs) have assumed a prominent place in geometric group theo
ry and related fields\,\nNow attention is also being focused on their (out
er) automorphism groups. The most well-understood examples of outer autom
orphism groups of RAAGs are $\\mathbf{GL}(n\,\\mathbb{Z})$ and $\\mathbf{O
ut}(F_n)$. $\\mathbf{GL}(n\,\\mathbb{Z})$ can be profitably studied via i
ts action on the symmetric space of marked lattices\, and $\\mathbf{Out}(F
_n)$ via its action on Outer space. We propose an analogous ``outer space
'' generalizing both of these\, on which the outer automorphism group of a
n arbitrary RAAG acts properly\, and we prove this space is contractible.
\n\nThis is joint work with Corey Bregman and Ruth Charney.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Maculan (Paris Sorbonne)
DTSTART:20200513T120000Z
DTEND:20200513T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/9
DESCRIPTION:Title: Affine vs. Stein varieties in complex and rigid geometry\nby Marco M
aculan (Paris Sorbonne) as part of Sapienza A&G Seminar\n\n\nAbstract\nSer
re’s GAGA theorem states that\, on a projective complex variety\, holomo
rphic objects (functions\, vector bundle and their sections\, etc.) are al
gebraic. Without compactness hypothesis this is not true. Yet\, one may wo
nder whether a variety that can be embedded holomorphically into an affine
space\, can be embedded therein algebraically. A classical example of Ser
re shows that the answer is negative.\n\nIn an ongoing joint work with J.
Poineau\, we investigate what happens when one replaces the complex number
s by the p-adic ones. Despite the formal similarities between the correspo
nding analytic theories\, the p-adic outcome is somewhat surprising.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valentino Tosatti (Northwestern University)
DTSTART:20200610T143000Z
DTEND:20200610T153000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/10
DESCRIPTION:Title: Metric limits of Calabi-Yau manifolds\nby Valentino Tosatti (Northw
estern University) as part of Sapienza A&G Seminar\n\n\nAbstract\nI will d
iscuss the problem of understanding the behavior of degenerating families
of Ricci-flat Kähler metrics on a Calabi-Yau manifold\, and what their po
ssible metric limits are. I will explain what we know in general about suc
h metric limits\, what techniques are used to approach these questions\, a
nd what applications these results have. \n\nBased on joint works with Gro
ss-Zhang and with Hein.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bojko Bakalov (North Carolina State University)
DTSTART:20200624T120000Z
DTEND:20200624T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/11
DESCRIPTION:Title: A vertex algebra construction of representations of toroidal Lie algebr
as\nby Bojko Bakalov (North Carolina State University) as part of Sapi
enza A&G Seminar\n\n\nAbstract\nGiven a simple finite-dimensional Lie alge
bra and an automorphism of finite order\, one can construct a twisted toro
idal Lie algebra.\nSimilarly to twisted affine Lie algebras\, which are we
ll-studied in the literature\, we can create representations of twisted to
roidal Lie algebras with the help of vertex algebras. In this talk\, I wil
l discuss twisted modules of vertex algebras and will show how representat
ions of twisted toroidal Lie algebras can be constructed from such twisted
modules.\n\nJoint work with Samantha Kirk.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J.-P. Demailly (Université Grenoble Alpes)
DTSTART:20201007T143000Z
DTEND:20201007T153000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/12
DESCRIPTION:Title: Hermitian-Yang-Mills approach to the conjecture of Griffiths on the pos
itivity of ample vector bundles\nby J.-P. Demailly (Université Grenob
le Alpes) as part of Sapienza A&G Seminar\n\n\nAbstract\nGiven a vector bu
ndle of arbitrary rank with ample determinant line bundle on a projective
manifold\, we propose a new elliptic system of differential equations of H
ermitian-Yang-Mills type for the curvature tensor.\nThe system is designed
so that solutions provide Hermitian metrics with positive curvature in th
e sense of Griffiths – and even in the dual Nakano sense. As a consequen
ce\, if an existence result could be obtained for every ample vector bundl
e\, the Griffiths conjecture on the equivalence between ampleness and posi
tivity of vector bundles would be settled. Another outcome of the approach
is a new concept of volume for vector bundles.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:D. Greb (Universität Duisburg-Essen)
DTSTART:20201021T120000Z
DTEND:20201021T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/13
DESCRIPTION:Title: Projective flatness over klt spaces and uniformisation of varieties wit
h nef anti-canonical divisor\nby D. Greb (Universität Duisburg-Essen)
as part of Sapienza A&G Seminar\n\n\nAbstract\nI will discuss a criterion
for the projectivisation of a reflexive sheaf on a klt space to be induce
d by a projective representation of the fundamental group of the smooth lo
cus. This criterion is then applied to give a characterisation of finite q
uotients of projective spaces and Abelian varieties by Q-Chern class (in)e
qualities and a suitable stability condition. This stability condition is
formulated in terms of a naturally defined extension of the tangent sheaf
by the structure sheaf. I will further examine cases in which this stabili
ty condition is satisfied\, comparing it to K-semistability and related no
tions. \nThis is joint work with Stefan Kebekus and Thomas Peternell.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:I. Bauer (Universität Bayreuth)
DTSTART:20201028T130000Z
DTEND:20201028T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/14
DESCRIPTION:Title: Rigid compact complex manifolds: recent results\, questions and conject
ures\nby I. Bauer (Universität Bayreuth) as part of Sapienza A&G Semi
nar\n\n\nAbstract\nThe aim of this talk is to give an update on recent ach
ievements and developments on rigid compact complex manifolds. I will star
t introducing different notions of rigidity and explaining the relations a
mong them. For curves all these notions coincide and the only rigid curve
is the projective line. For surfaces rigidity is still quite „rare“\,
since the only rigid surfaces which are not minimal of general type are De
l Pezzo surfaces of degree at least 5 and Inoue surfaces. \nIn higher dime
nsion the geography of rigid manifolds gets much richer. \nThen I will rep
ort on an answer to a more than 40 years open question of Morrow and Kodai
ra\, exhibiting an infinite series of rigid but not infinitesimally rigid
surfaces of general type. \nI will conclude addressing open questions and
conjectures.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:B. Hanke (Universität Augsburg)
DTSTART:20201104T130000Z
DTEND:20201104T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/15
DESCRIPTION:Title: Scalar positive immersions\nby B. Hanke (Universität Augsburg) as
part of Sapienza A&G Seminar\n\n\nAbstract\nAs shown by Gromov-Lawson and
Stolz the only obstruction to the existence of positive scalar curvature m
etrics on closed simply connected manifolds in dimensions at least five ap
pears on spin manifolds\, and is given by the non-vanishing of the α-genu
s of Hitchin.\nWhen unobstructed we shall realise a positive scalar curvat
ure metric by an immersion into Euclidean space whose dimension is uniform
ly close to the classical Whitney upper bound for smooth immersions. \nOur
main tool is an extrinsic counterpart of the well-known Gromov-Lawson sur
gery procedure for constructing positive scalar curvature metrics. At this
point we use the local flexibility lemma proven by Christian Bär and the
speaker. \nThis is joint work with Luis Florit\, IMPA (Rio de Janeiro).\n
LOCATION:https://researchseminars.org/talk/AGSeminar/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:G. Röhrle (Ruhr-Universität Bochum)
DTSTART:20201014T120000Z
DTEND:20201014T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/16
DESCRIPTION:Title: On a relative version of Serre's notion of G-complete reducibility\
nby G. Röhrle (Ruhr-Universität Bochum) as part of Sapienza A&G Seminar\
n\n\nAbstract\nWe first review some basic results related to Serre's notio
n of G-complete reducibility for a reductive algebraic group G. We then di
scuss a relative variant of this concept where we let K be a reductive sub
group of G\, and consider subgroups of G which normalise the identity comp
onent $K^\\circ$ of K. We show that such a subgroup is relatively G-comple
tely reducible with respect to K if and only if its image in the automorph
ism group of $K^\\circ$ is completely reducible in the sense of Serre. Thi
s allows us to generalise a number of fundamental results from the absolut
e to the relative setting. This is a report on recent joint work with M. G
ruchot and A. Litterick.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:I. van Santen (Universität Basel)
DTSTART:20201111T130000Z
DTEND:20201111T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/17
DESCRIPTION:Title: Embeddings of smooth affine varieties into algebraic groups\nby I.
van Santen (Universität Basel) as part of Sapienza A&G Seminar\n\n\nAbstr
act\nThis is joint work with Peter Feller. In any category there are the f
ollowing fundamental problems concerning embeddings from an object Z into
another object X:\n\n(Existence) Does there exist an embedding of Z into X
? \n(Uniqueness) Having two embeddings f\, g of Z into X\, does there e
xists an automorphism ψ of X such that g = ψ ◦ f?\n\nIn this talk\
, we will mainly focus on the first problem in the category of affine vari
eties\, where Z is smooth and X is an algebraic group. Amongst other thing
s\, we will discuss the following result.\n\nTheorem. For every simple alg
ebraic group G and every smooth affine variety Z with dim G > 2dim Z + 1\,
there exists an embedding of Z into G.\n\nThe proof is based upon paramet
ric transversality results for flexible affine varieties due to Kaliman. W
e will also discuss the following result\, which implies the optimality of
the above existence result up to a possible improvement of the dimension
bound by one. It’s proof is an adaptation of a Chow-group-based argument
due to Bloch\, Murthy\, and Szpiro for the affine space.\n\nProposition.
For every non-finite algebraic group G and every d ≥ dim G / 2\, there e
xists an irreducible smooth affine variety of dimension d that does not ad
mit an embedding into G.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J. Draisma (Universität Bern)
DTSTART:20201118T130000Z
DTEND:20201118T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/18
DESCRIPTION:Title: The geometry of polynomial functors\nby J. Draisma (Universität Be
rn) as part of Sapienza A&G Seminar\n\n\nAbstract\nA polynomial functor P
is a functor from the category of finite-dimensional vector spaces to itse
lf such that for every U\,V the map Hom(U\,V) -> Hom(P(U)\,P(V)) is polyno
mial. In characteristic zero\, P is a direct sum of Schur functors.\n\nThi
s talk concerns closed subsets of such P\, i.e.\, rules that assign to a v
ector space V a closed subset X(V) of P(V) such that P(phi)X(U) is contain
ed in X(V) for every linear map phi:U -> V.\n\nQuite surprisingly\, these
behave very much like finite-dimensional affine varieties. For instance\,
they satisfy the descending chain condition and a version of Chevalley's t
heorem on constructible sets. I will discuss these results and more. The t
alk is based on joint work with Arthur Bik\, Rob Eggermont\, and Andrew Sn
owden.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:C. Araujo (IMPA)
DTSTART:20201125T130000Z
DTEND:20201125T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/19
DESCRIPTION:Title: Birational geometry of Calabi-Yau pairs and 3-dimensional Cremona trans
formations\nby C. Araujo (IMPA) as part of Sapienza A&G Seminar\n\n\nA
bstract\nRecently\, Oguiso addressed the following question\, attributed t
o Gizatullin: "Which automorphisms of a smooth quartic K3 surface $D\\subs
et \\mathbb P^3$ are induced by Cremona transformations of the ambient spa
ce $\\mathbb{P}^3$?'' When $D\\subset \\mathbb{P}^3$ is a smooth quartic
surface\, $(\\mathbb{P}^3\,D)$ is an example of a Calabi-Yau pair\, that i
s\, a pair $(X\,D)$\, consisting of a normal projective variety $X$ and an
effective Weil divisor $D$ on $X$ such that $K_X+D\\sim 0$. The above que
stion is really about birational properties of the Calabi-Yau pair $(\\mat
hbb{P}^3\,D)$. In this talk\, I will explain a general framework to study
the birational geometry of mildly singular Calabi-Yau pairs. Then I will f
ocus on the case of singular quartic surfaces $D\\subset \\mathbb{P}^3$. O
ur results illustrate how the appearance of increasingly worse singulariti
es in $D$ enriches the birational geometry of the pair $(\\mathbb{P}^3\, D
)$\, and lead to interesting subgroups of the Cremona group of $\\mathbb{P
}^3$. This is joint work with Alessio Corti and Alex Massarenti.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:E. Sommers (University of Massachusetts Amherst)
DTSTART:20201209T130000Z
DTEND:20201209T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/20
DESCRIPTION:Title: The geometry of nilpotent varieties via subbundles of the cotangent bun
dle\nby E. Sommers (University of Massachusetts Amherst) as part of Sa
pienza A&G Seminar\n\n\nAbstract\nLet $G$ be a simple algebraic group with
flag variety $G/B$. \nThe Springer resolution is the moment map from the
cotangent bundle of $G/B$ to the (dual of the) Lie algebra $\\mathfrak{g}$
of $G$. The cohomology of the fibers of this map play an important role
in the representation theory of $G$ over various fields.\n\nIdentify the c
otangent bundle with the vector bundle $G \\times^B \\mathfrak{n}$\, where
$\\mathfrak{n}$ is the nilradical of the Lie algebra of $B$. There are s
ubbundles $G \\times^B I$ for each subspace $I \\subset \\mathfrak{n}$ tha
t is $B$-stable\, and maps $p_I: G \\times^B I \\to \\mathfrak{g}$. The
fibers of $p_I$ are also interesting and their cohomology relates to an in
tersection cohomology complex on the image of $p_I$\, a nilpotent variety.
\n\nIn this talk we discuss two topics: (1) methods for computing the co
homology of the fibers of $p_I$\; (2) a vanishing theorem/conjecture for t
he cohomology of the structure sheaf on these subbundles.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:G. Carron (Université de Nantes)
DTSTART:20201216T130000Z
DTEND:20201216T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/21
DESCRIPTION:Title: A Bonnet-Myers Theorem from a spectral assumption\nby G. Carron (Un
iversité de Nantes) as part of Sapienza A&G Seminar\n\n\nAbstract\nWe obt
ain a finiteness result for the fundamental group of a closed Riemannian m
anifold $(M^n\,g)$ under the assumption that the Schrödinger operator $\\
Delta_g+(n-2)/\\rho$ is positive (where at $x\\in M$\, $\\rho(x)$ is the l
owest eigenvalue of the Ricci tensor at $x$).\nIt is a joint work with C.
Rose (MPI Leipzig).\n
LOCATION:https://researchseminars.org/talk/AGSeminar/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:E. Floris (Université de Poitiers)
DTSTART:20210120T130000Z
DTEND:20210120T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/22
DESCRIPTION:Title: Connected algebraic groups acting on Fano fibrations over P^1\nby E
. Floris (Université de Poitiers) as part of Sapienza A&G Seminar\n\n\nAb
stract\nLet $G$ be a connected algebraic group and $X$ a variety endowed w
ith a regular action of $G$ and a Mori fibre space $X/\\mathbb P^1$ whose
fibre is a Fano variety of Picard rank at least 2.\nIn this talk I will ex
plain why there is a proper horizontal subvariety of $X$ which is invarian
t under the action of $G$\, alongside with some applications of this resul
t to the classification of connected algebraic subgroups of the Cremona gr
oup in dimension 4.\nThis is a joint work with Jérémy Blanc.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:K. Baur (University of Leeds)
DTSTART:20210113T130000Z
DTEND:20210113T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/23
DESCRIPTION:Title: Cluster structures for Grassmannians\nby K. Baur (University of Lee
ds) as part of Sapienza A&G Seminar\n\n\nAbstract\nThe coordinate ring of
the Grassmannian has the structure of a cluster algebra. On the other side
\, the category of maximal CM modules over a certain infinite dimensional
algebra Is a cluster category associated to this cluster algebra structure
. We study this category\, in particular in the tame cases. We also show h
ow to associate frieze patterns to these cluster structures.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J. Weyman (Jagiellonian University in Kraków)
DTSTART:20210127T130000Z
DTEND:20210127T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/24
DESCRIPTION:Title: Finite Free Resolutions and opposite Schubert varieties\nby J. Weym
an (Jagiellonian University in Kraków) as part of Sapienza A&G Seminar\n\
n\nAbstract\nIn the first part of this talk I will give an update on the c
onnection between perfect ideals of codimension 3 and Schubert varieties o
f exceptional groups (and more generally opposite Schubert varieties for K
ac-Moody groups associated to T-shaped graphs $T_{pqr}$). I will also disc
uss a parallel theory which points to similar connection between Gorenstei
n ideals of codimension 4 with n generators and opposite Schubert varietie
s in homogeneous spaces related to a Kac-Moody group of type $\\mathsf E_n
$.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:V. Balaji (Chennai Mathematical Institute)
DTSTART:20210203T130000Z
DTEND:20210203T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/25
DESCRIPTION:Title: On a "wonderful" Bruhat-Tits group scheme\nby V. Balaji (Chennai Ma
thematical Institute) as part of Sapienza A&G Seminar\n\n\nAbstract\nWe ma
ke a universal construction of Bruhat-Tits group scheme on wonderful embed
dings of adjoint groups in the absolute and relative settings of adjoint K
ac-Moody groups. These group schemes have natural classifying properties r
eflecting the orbit structure on the wonderful embeddings. A theme which i
s reflected in the work is that the various wonderful embeddings give alge
bra-geometric realizations of the different kinds of buildings. This shows
an intimate relationship between the wonderful embeddings and Bruhat-Tits
theory.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A. Kuznetsov (Steklov Mathematical Institute)
DTSTART:20210210T130000Z
DTEND:20210210T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/26
DESCRIPTION:Title: Lefschetz collections and residual categories for Grassmannians\nby
A. Kuznetsov (Steklov Mathematical Institute) as part of Sapienza A&G Sem
inar\n\n\nAbstract\nI will try to explain and motivate the notion of Lefsc
hetz (exceptional) collections in derived categories of coherent sheaves a
nd their residual categories and\, in particular\, its conjectural relatio
n to quantum cohomology. If time permits\, I will discuss recent progress
in construction of Lefschetz collections for Grassmannians of classical gr
oups. This is joint work with Maxim Smirnov.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:M. Jonsson (University of Michigan)
DTSTART:20210217T130000Z
DTEND:20210217T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/27
DESCRIPTION:Title: Filtrations on section rings and non-Archimedean geometry\nby M. Jo
nsson (University of Michigan) as part of Sapienza A&G Seminar\n\n\nAbstra
ct\nTo any polarized variety (X\,L) is associated a section ring R. I will
explain the relation between suitable classes of norms on R and functions
on the Berkovich analytification of X. Time permitting\, I will discuss a
pplications of this to K-stability. This is joint work with S. Boucksom.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:R. Wentworth (University of Maryland)
DTSTART:20210303T130000Z
DTEND:20210303T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/28
DESCRIPTION:Title: Conformal limits of parabolic Higgs bundles\nby R. Wentworth (Unive
rsity of Maryland) as part of Sapienza A&G Seminar\n\n\nAbstract\nGaiotto
introduced the notion of a conformal limit of a Higgs bundle and conjectur
ed that these should\nidentify the Hitchin component with the Oper stratum
in the deRham moduli space. \nIn the case of closed Riemann surfaces this
result was proven by Dumitrescu\, et al.\, and the limits were shown to e
xist much more generally by Collier and the speaker. \nIn this talk I will
report on progress in the case of parabolic Higgs bundles\, which were th
e context of Gaiotto's original conjecture. \nThis is joint work with B. C
ollier and L. Fredrickson.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:F. Rochon (Université du Québec à Montréal)
DTSTART:20210324T130000Z
DTEND:20210324T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/29
DESCRIPTION:Title: L^2-cohomology of quasi-fibered boundary metrics\nby F. Rochon (Uni
versité du Québec à Montréal) as part of Sapienza A&G Seminar\n\n\nAbs
tract\nQuasi-fibered boundary metrics (QFB metrics) form a class of comple
te metrics generalizing the class of quasi-asymptotically locally Euclidea
n metrics introduced by Joyce. \nAfter reviewing what QFB metrics are and
presenting natural examples\, we will present a new approach to compute t
he L^2-cohomology of such metrics. \nThis is based on a joint work with C
hris Kottke.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J. Martens (University of Edinburgh)
DTSTART:20210407T120000Z
DTEND:20210407T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/30
DESCRIPTION:Title: Sporadic behaviour of quantum representations and rank-level duality\nby J. Martens (University of Edinburgh) as part of Sapienza A&G Seminar
\n\n\nAbstract\nThe theory of conformal blocks provides us with projective
representations of the mapping class group. These can equivalently also b
e constructed from the point of view of non-abelian theta functions\, via
the Hitchin connection. It has been known for some time that\, for SL(2)\
, these representations have infinite order\, with the exception of some s
poradic low levels. We will discuss how some of these sporadic cases can
be understood via rank-level duality.\nThis is joint work with Baier\, Bol
ognesi and Pauly.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:C. Procesi (Sapienza Università di Roma)
DTSTART:20210224T130000Z
DTEND:20210224T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/31
DESCRIPTION:Title: A note on the Weingarten funtion\nby C. Procesi (Sapienza Universit
à di Roma) as part of Sapienza A&G Seminar\n\n\nAbstract\nI will compare
work of Formanek on a certain construction of central polynomials with tha
t of Collins on integration on unitary groups. These two quite disjoint to
pics share the construction of the same function on the symmetric group\,
which the second author calls Weingarten function. By joining these two ap
proaches we succeed in giving a simplified and very natural presentation o
f both Formanek and Collins's Theory.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:D. Alessandrini (Columbia University)
DTSTART:20210310T130000Z
DTEND:20210310T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/32
DESCRIPTION:Title: Non commutative cluster coordinates for Higher Teichmüller Spaces\
nby D. Alessandrini (Columbia University) as part of Sapienza A&G Seminar\
n\n\nAbstract\nIn higher Teichmuller theory we study subsets of the charac
ter varieties of surface groups that are higher rank analogs of Teichmulle
r spaces\, e.g. the Hitchin components and the spaces of maximal represent
ations.\nFock-Goncharov generalized Thurston's shear coordinates and Penne
r's Lambda-lengths to the Hitchin components\, showing that they have a be
autiful structure of cluster variety.\nHere we apply similar ideas to Maxi
mal Representations and we find new coordinates on these spaces that give
them a structure of non-commutative cluster varieties\, in the sense defin
ed by Berenstein-Rethak.\nThis is joint work with Guichard\, Rogozinnikov
and Wienhard.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:S. Scherotzke (Université du Luxembourg)
DTSTART:20210414T120000Z
DTEND:20210414T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/33
DESCRIPTION:Title: The categorified Grothendieck-Riemann-Roch Theorem\nby S. Scherotzk
e (Université du Luxembourg) as part of Sapienza A&G Seminar\n\n\nAbstrac
t\nThe Chern character is a central construction which appears in topology
\, representation theory and algebraic geometry. \nIn algebraic topology i
t is for instance used to probe algebraic K-theory which is notoriously ha
rd to compute\, in representation theory it takes the form of classical ch
aracter theory. Recently\, Toen and Vezzosi suggested a construction\, usi
ng derived algebraic geometry\, which allows to unify the various Chern ch
aracters. \nWe will categorify this Chern character. In the categorified p
icture algebraic K-theory is replaced by the category of non-commutative m
otives. It turns out that the categorified Chern character has many intere
sting applications. For instance we show that the DeRham realisation funct
or is of non-commutative origin.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:D. Testerman (École polytechnique fédérale de Lausanne)
DTSTART:20210428T120000Z
DTEND:20210428T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/34
DESCRIPTION:Title: Overgroups of regular unipotent elements in simple algebraic groups
\nby D. Testerman (École polytechnique fédérale de Lausanne) as part of
Sapienza A&G Seminar\n\n\nAbstract\nWe consider the question of determini
ng reductive overgroups of regular unipotent elements in simple algebraic
groups and in particular give a condition which guarantees that the overgr
oup does not lie in a proper parabolic subgroup of the ambient simple grou
p. This is joint work with Gunter Malle\, and follows on work of Suprunenk
o\, Saxl and Seitz\, and Testerman and Zalesski.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:R. Schoof (Università di Roma "Tor Vergata")
DTSTART:20210512T120000Z
DTEND:20210512T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/35
DESCRIPTION:Title: Finite flat group schemes over Z\nby R. Schoof (Università di Roma
"Tor Vergata") as part of Sapienza A&G Seminar\n\n\nAbstract\nFinite flat
group schemes are important in number theory.\nWe explain what we do and
don't know about their structure\nover rings of integers of number fields\
, in particular over $\\mathbb Z$.\nThis is joint work with Lassina Dembel
e.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A. Lonjou (Université Paris-Saclay)
DTSTART:20210317T130000Z
DTEND:20210317T140000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/36
DESCRIPTION:Title: Actions of Cremona groups on CAT(0) cube complexes\nby A. Lonjou (U
niversité Paris-Saclay) as part of Sapienza A&G Seminar\n\n\nAbstract\nA
key tool to study the plane Cremona group is its action on a hyperbolic sp
ace. Sadly\, in higher rank such an action is not available. \nRecently\,
in geometric group theory\, actions on CAT(0) cube complexes turned out to
be a powerful tool to study a large class of groups. \nIn this talk\, bas
ed on a common work with Christian Urech\, we will construct such complexe
s on which Cremona groups of rank n act. Then\, we will see which kind of
results on these groups we can obtain.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:M. Păun (Universität Bayreuth)
DTSTART:20210616T120000Z
DTEND:20210616T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/37
DESCRIPTION:Title: On extension of twisted canonical forms defined on the central fiber of
a Kähler family\nby M. Păun (Universität Bayreuth) as part of Sapi
enza A&G Seminar\n\n\nAbstract\nWe will report on a joint work with J. Cao
. \nOur main result establishes the extension of twisted canonical forms d
efined on an infinitesimal neighborhood of the central fiber of a Kahler f
amily under a natural $L^2$ hypothesis.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A. Wienhard (Universität Heidelberg)
DTSTART:20210623T123000Z
DTEND:20210623T133000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/38
DESCRIPTION:Title: Where geometry meets dynamics: groups\, entropy and Hausdorff dimension
\nby A. Wienhard (Universität Heidelberg) as part of Sapienza A&G Sem
inar\n\n\nAbstract\nI will discuss geometric and dynamical properties of a
ctions of discrete groups on Riemannian symmetric spaces. \nI will highlig
ht some aspects of the interplay between geometry and dynamics\, and prese
nt some recent results which generalize theorems of Sullivan\, Bridgeman-T
aylor\, McMullen for convex cocompact subgroups acting on hyperbolic space
in the framework of discrete subgroups of Lie groups of higher rank.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J. Kollár (Princeton University)
DTSTART:20210630T120000Z
DTEND:20210630T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/39
DESCRIPTION:Title: Deformations of varieties of general type\nby J. Kollár (Princeton
University) as part of Sapienza A&G Seminar\n\n\nAbstract\nWe prove that
small deformations of a projective variety of general type are also projec
tive varieties of general type\, with the same plurigenera.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:E. Rousseau (Aix-Marseille Université)
DTSTART:20210519T120000Z
DTEND:20210519T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/40
DESCRIPTION:Title: Numerically special varieties\nby E. Rousseau (Aix-Marseille Univer
sité) as part of Sapienza A&G Seminar\n\n\nAbstract\nCampana introduced t
he class of special varieties as the varieties admitting no maps onto an o
rbifold of general type. They are also characterized by the non-existence
of Bogomolov sheaves which are rank one coherent subsheaves of maximal Kod
aira dimension in some exterior power of the cotangent bundle. \nCampana h
as conjectured that one can replace the Kodaira dimension by the numerical
dimension in this characterization. \nWe prove partially this conjecture
showing that a projective manifold admitting a rank one coherent subsheaf
of the cotangent bundle with numerical dimension 1 is not special. \nThis
is a joint work with J.V. Pereira and F. Touzet.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:V. F. Zenobi (Sapienza Università di Roma)
DTSTART:20210421T120000Z
DTEND:20210421T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/41
DESCRIPTION:Title: Higher rho numbers and metrics of positive scalar curvature\nby V.
F. Zenobi (Sapienza Università di Roma) as part of Sapienza A&G Seminar\n
\n\nAbstract\nThe analytic surgery sequence is a long exact sequence of K-
theory groups which combines topological information (the K-homology of ma
nifolds)\, index theoretic information (the K-theory of group C*-algebras)
\, and secondary index information (the analytic structure group of Higson
-Roe). We will see how to give a definition of terms based entirely on alg
ebras of pseudodifferential operators and their K-theory. We use this to s
ystematically develop maps to an exact sequence of non-commutative de Rham
homology/cyclic homology. Via pairings with cyclic cohomology classes\, t
his gives rise to new numeric secondary index invariants (higher rho numbe
rs) with explicit formulas and calculation tools due to the compatibility
in the whole sequence. We use this for geometric applications. In particul
ar\, we derive new information about the moduli space of Riemannian metric
s of positive scalar curvature\, where we give new lower bounds on the num
ber of its components.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Z. Patakfalvi (École polytechnique fédérale de Lausanne)
DTSTART:20210505T120000Z
DTEND:20210505T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/42
DESCRIPTION:Title: Replacing vanishing theorems in mixed characteristic and the Minimal Mo
del Program for 3-folds over excellent schemes\nby Z. Patakfalvi (Éco
le polytechnique fédérale de Lausanne) as part of Sapienza A&G Seminar\n
\n\nAbstract\nKodaira and Kawamata-Viehweg vanishing is frequently used to
lift sections of adjoint bundles\, a crucial part of many arguments in th
e classification theory of algebraic varieties\, notably in many proofs of
the Minimal Model Program. These vanishing theorems fail in mixed charact
eristic situations\, for example for \n1.) proper\, flat schemes over the
p-adic numbers\, or \n2.) proper birational models of mixed characteristic
local rings. \nI present a work that remedies this situation to some exte
nt. In particular\, we are able to \na.) show Kodaira and Kawamata-Viehweg
vanishing in many situations\, \nb.) prove the 3-dimensional Minimal Mod
el Program for excellent schemes\, and \nc.) draw geometric corollaries of
point b.) to the existence of the moduli space of stable surfaces in mixe
d characteristic. \nThis is a joint work with Bhargav Bhatt\, Linquan Ma\,
Karl Schwede\, Kevin Tucker\, Joe Waldron and Jakub Witaszek.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:S. Riche (Université Clermont Auvergne)
DTSTART:20210526T120000Z
DTEND:20210526T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/43
DESCRIPTION:Title: Perverse sheaves on affine flag varieties\, geometry of the dual group\
, and representations\nby S. Riche (Université Clermont Auvergne) as
part of Sapienza A&G Seminar\n\n\nAbstract\nThe description of regular blo
cks of the category O of a complex semisimple Lie algebra in terms of perv
erse sheaves on a flag variety has been a crucial tool for its study\, and
in particular for the proof of the Kazhdan-Lusztig character formula. Thi
s description has a conjectural analogue for representations of reductive
groups over fields of positive characteristic\, as predicted by Finkelberg
-Mirkovic\, which involves a category of perverse sheaves on the affine Gr
assmannian of the Langlands dual group\, with coefficients in a field of p
ositive characteristic. In this talk I will present a work in progress wit
h Bezrukavnikov which we expect will lead to a proof of this conjecture. A
s a step towards this goal\, we obtain a description of tilting perverse s
heaves on the affine flag variety reminiscent of the corresponding result
for usual flag varieties due to Soergel.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:J. Ruppenthal (Bergische Universität Wuppertal)
DTSTART:20210609T120000Z
DTEND:20210609T130000Z
DTSTAMP:20260422T214955Z
UID:AGSeminar/44
DESCRIPTION:Title: Canonical sheaves at isolated canonical singularities\nby J. Ruppen
thal (Bergische Universität Wuppertal) as part of Sapienza A&G Seminar\n\
n\nAbstract\nThe canonical line bundle and the corresponding canonical she
af\nbelong to the most important geometric/analytic objects\nassociated to
a complex manifold. They play a crucial role e.g.\nin classification theo
ry\, Serre duality or vanishing theorems.\nIf we consider singular varieti
es instead of smooth manifolds\,\nthen there exist various possibilities t
o generalize the canonical sheaf\nto that setting. One can consider for ex
ample the Grothendieck(-Barlet-Henkin-Passare)\ndualizing sheaf or the Gra
uert-Riemenschneider L2-sheaf.\nIn this talk\, we will discuss another pos
sible generalization\, i.e.\,\nthe sheaf of L2 holomorphic n-forms with a
certain boundary\ncondition at the singular set. This sheaf is essential f
or L2-dbar-theory\non singular spaces\, but difficult to understand. We wi
ll describe it\nexplicitly for isolated canonical Gorenstein singularities
.\n
LOCATION:https://researchseminars.org/talk/AGSeminar/44/
END:VEVENT
END:VCALENDAR