Publications and preprints
- Determinantal
identities for flagged Schur and Schubert polynomials
(with G. Merzon)
European Journal of Mathematics, 19 pages, to appear in 2016
[arXiv] [PDF]We prove new determinantal identities for a family of flagged Schur polynomials. As a corollary of these identities we obtain determinantal expressions of Schubert polynomials for certain vexillary permutations.
- Ribbon graphs and bialgebra of Lagrangian
subspaces (with V.Kleptsyn)
Journal of Knot Theory and its Ramifications, 26 pages, to appear in S. V. Duzhin memorial volume (2016).
[arXiv] [PDF]To each ribbon graph we assign a so-called L-space, which is a Lagrangian subspace in an even-dimensional vector space with the standard symplectic form. This invariant generalizes the notion of the intersection matrix of a chord diagram. Moreover, the actions of Morse perestroikas (or taking a partial dual) and Vassiliev moves on ribbon graphs are reinterpreted nicely in the language of L-spaces, becoming changes of bases in this vector space. Finally, we define a bialgebra structure on the span of L-spaces, which is analogous to the 4-bialgebra structure on chord diagrams.
- Schubert calculus
and Gelfand-Zetlin polytopes (joint with
V. Kiritchenko and V. Timorin)
Russian Mathematical Surveys, 64:4, 685-719 (2012)
[arXiv] [PDF] [PDF (in Russian)]We describe a new approach to the Schubert calculus on complete flag varieties using the volume polynomial associated with Gelfand-Zetlin polytopes. This approach allows us to compute the intersection products of Schubert cycles by intersecting faces of a polytope.
- Springer fiber components in the two columns case for types A
and D are normal (joint with N. Perrin)
Bulletin de la Société Mathématique de France, 140:3, 309-333 (2012)
[arXiv] [PDF]We study the singularities of the irreducible components of the Springer fiber over a nilpotent element N with N2=0 in a Lie algebra of type A or D (the so-called two columns case). We use Frobenius splitting techniques to prove that these irreducible components are normal, Cohen-Macaulay, and have rational singularities.
- Desingularizations of Schubert varieties in double
Grassmannians
Functional Analysis and its Applications 42:2, 126-134 (2008)
[arXiv] [PDF] [PDF (in Russian)]Let X be the direct product of two Grassmann varieties of k- and l-planes in a finite-dimensional vector space V, and let B be the isotropy group of a complete flag in V. We consider B-orbits in X, which are an analog to Schubert cells in Grassmannians. We describe this set of orbits combinatorially and construct desingularizations for the closures of these orbits, similar to the Bott--Samelson desingularizations for Schubert varieties.
2007 - Bruhat order for two subspaces and a flag
Preprint, 30 pages
[arXiv] [PDF]The classical Ehresmann-Bruhat order describes the possible degenerations of a pair of flags in a finite-dimensional vector space V; or, equivalently, the closure of an orbit of the group GL(V) acting on the direct product of two full flag varieties. We obtain a similar result for triples consisting of two subspaces and a partial flag in V; this is equivalent to describing the closure of a GL(V)-orbit in the product of two Grassmannians and one flag variety. We give a rank criterion to check whether such a triple can be degenerated to another one, and we classify the minimal degenerations. Our methods involve only elementary linear algebra and combinatorics of graphs (originating in Auslander-Reiten quivers).
- Orbites d'un sous-groupe de Borel dans le produit de deux
grassmanniennes (Orbits of a Borel subgroup on the direct product of two
Grassmannians) Ph. D. thesis (in English, with an
introduction in French)
[PDF, 1,7 Mb] - On generating sets of ideals defining S-varieties
Moscow Univ. Math. Bull. 60 (2005), no. 3, 1-4 (2006)
[PDF] [PDF (in Russian)].Let G be a semisimple algebraic group. A theorem due to Kostant describes the ideal defining the G-orbit closure of the sum of highest-weight vectors in a (reducible) G-module, such that the corresponding highest weights are linearly independent. This ideal is generated by quadratic polynomials. In this paper we generalize this result, assuming that the highest weights can be linearly dependent. In this case the equations defining these varieties are not necessary quadratic.
Expository texts, refereed proceedings
- Grassmannians, flag varieties, and Gelfand-Zetlin
polytopes 47 pages, to appear in More Lectures in Representation Theory (Proceedings of
Maurice Auslander Distinguished Lectures and International
Conference), Contemporary Mathematics series, AMS, 2016.
[arXiv] [PDF]The aim of these notes is to give an introduction into Schubert calculus on Grassmannians and flag varieties. We discuss various aspects of Schubert calculus, such as applications to enumerative geometry, structure of the cohomology rings of Grassmannians and flag varieties, Schur and Schubert polynomials. We conclude with a survey of results of V. Kiritchenko, V. Timorin and the author on a new approach to Schubert calculus on full flag varieties via combinatorics of Gelfand-Zetlin polytopes.
These are extended notes of a talk given at Maurice Auslander Distinguished Lectures and International Conference in April 2013. - Convex chains for Schubert varieties (joint with
V. Kiritchenko and V. Timorin)
Oberwolfach reports, 41/2011, 15-18.
[PDF]This is an extended abstract of Valentina Kiritchenko's talk on the Oberwolfach meeting «New developments in Newton-Okounkov bodies» in August, 2011. We define analogs of Demazure operators acting on convex polytopes. This leads to a simple inductive construction of Gelfand-Zetlin polytopes and their generalizations.
- Gelfand-Zetlin polytopes and Demazure characters (joint with
V. Kiritchenko and V. Timorin)
Proceedings of the International Conference «50 years of IITP», ISBN 978-5-901158-15-9, 5 pages
[PDF]This is a short self-contained exposition of our formula for the Demazure characters of Schubert varieties in terms of the exponential sums over faces of Gelfand-Zetlin polytopes. All necessary definitions are given in the text.
Educational texts, popularization of mathematics
- Ideas of Newton-Okounkov bodies (joint with
V. Kiritchenko and V. Timorin)
Snapshots of Modern Mathematics from Oberwolfach, 8/2015
[MFO website] [PDF]
In this snapshot, we will consider the problem of finding the number of solutions to a given system of polynomial equations. This question leads to the theory of Newton polytopes and Newton-Okounkov bodies of which we will give a basic notion.
- Young diagrams and q-combinatorics Kvant No.
1, 2015, pp. 7–12, in Russian
[PDF]In this paper for high school students we introduce Gaussian binomial coefficients and discuss their properties, comparing them to well-known theorems from ``ordinary'' combinatorics. We also obtain classical results due to Euler about the generating function for partitions.
- Three glances on the Aztec diamond
MCCME, Moscow (2015). 48 pages, in Russian
[PDF]We discuss three proofs of the Aztec diamond theorem, stating that the number of domino tilings of an Aztec diamond of rank n equals 2n(n+1)/2.
These are the notes of a mini-course given at the Summer school “Contemporary Mathematics” in Dubna, Russia, in July 2014. - Young diagrams, plane partitions and alternating sign
matrices
MCCME, Moscow (2014). 64 pages, in Russian
[PDF]How many ways are there to decompose a natural number into several summands, if two sums that differ only in the order of their summands are considered the same partition? It turns out that there is no simple answer to this seemingly elementary question. However, this question gives rise to a very interesting theory, and the results of this theory have applications in various branches of mathematics and mathematical physics.
These are the notes of a mini-course given at the Summer school “Contemporary Mathematics” in Dubna, Russia, in July 2013. - Reflection groups and regular polyhedra
MCCME, Moscow (2009). 48 pages, in Russian
[PDF]Notes of my mini-course for undergraduate students given at the Summer school “Contemporary Mathematics” in Dubna, Russia, in July 2008. The main goal of these notes is to prove Schläfli's theorem on the classification of regular polyhedra in an n-dimensional space. As a byproduct of our proof, we obtain a classification of finite reflection groups in a Euclidean space.
Selected presentations
- Schubert
polynomials and rc-graphs
[PDF]
Meeting of Generations (Dynasty Foundation conference), Moscow, June 9–11, 2015 - Partitions and Young
diagrams: from Euler to our days
Slides [PDF] Problem set [PDF]
« Junior Data Analysis School» (Malyi ShAD), Yandex, Moscow, Russia, February 14, 2015, in Russian.
An expository talk for high school students on combinatorics of Young diagrams and related objects. - Schubert polynomials and
pipe dreams
[PDF]
Topology of Torus Actions and Applications to Geometry and Combinatorics (ICM Satellite Conference), Daejeon, Republic of Korea, August 7, 2014 - Symmetry in mathematics
and beyond
[PDF]
Polytechnic Museum, Moscow, Russia, October 8, 2013, in Russian.
This is a lecture for general audience on various appearances of symmetry in nature, art and mathematics. - Schubert polynomials,
pipe dreams and associahedra
[PDF]
Algebra and Geometry: International conference in honor of Askold Khovanskii's 65th birthday. Moscow, Russia, June 4, 2012 - Schubert calculus and Gelfand-Zetlin
polytopes
[PDF]
International Conference on Representations of Algebras (ICRA XIV), Tokyo, August 12, 2010