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We study unirationality of actions of finite groups on Fano threefolds.

Algebraic Geometry · Mathematics 2025-02-28 Ivan Cheltsov , Yuri Tschinkel , Zhijia Zhang

Fix a finite group $G$. We seek to classify varieties with $G$-action equivariantly birational to a representation of $G$ on affine or projective space. Our focus is odd-dimensional smooth complete intersections of two quadrics, relating…

Algebraic Geometry · Mathematics 2022-02-02 Brendan Hassett , Yuri Tschinkel

We list all finite abelian groups which act effectively on smooth cubic fourfolds.

Algebraic Geometry · Mathematics 2013-09-03 Evgeny Mayanskiy

We consider groups G which have a cocompact, 3-manifold model for the classifying space \underline{E}G. We provide an algorithm for computing the rationalized equivariant K-homology of \underline{E}G. Under the additional hypothesis that…

K-Theory and Homology · Mathematics 2013-04-30 Jean-François Lafont , Ivonne J. Ortiz , Rubén J. Sánchez-García

We study cohomological obstructions to equivariant unirationality, with special regard to actions of finite groups on del Pezzo surfaces and Fano threefolds.

Algebraic Geometry · Mathematics 2025-04-15 Yuri Tschinkel , Zhijia Zhang

A smooth cuboid can be identified with a $3\times 3$ matrix of linear forms, with coefficients in a field $K$, whose determinant describes a smooth cubic in the projective plane. To each such matrix one can associate a group scheme over…

Group Theory · Mathematics 2025-04-23 Joshua Maglione , Mima Stanojkovski

We develop the formalism of universal torsors in equivariant birational geometry and apply it to produce new examples of nonbirational but stably birational actions of finite groups.

Algebraic Geometry · Mathematics 2022-04-08 Brendan Hassett , Yuri Tschinkel

Aim of this paper is to define a new type of cohomology for multiplicative Hom-Leibniz algebras which controls deformations of Hom-Leibniz algebra structure. The cohomology and the associated deformation theory for Hom-Leibniz algebras as…

Rings and Algebras · Mathematics 2020-11-23 Goutam Mukherjee , Ripan Saha

We study equivariant morphisms from zero dimensional schemes to varieties and show that, under suitable assumptions, all such morphisms factor via a canonical one. We relate the above to Algebraic Representations of Ergodic Actions.

Algebraic Geometry · Mathematics 2023-04-05 Avraham Aizenbud , Uri Bader

We investigate equivariant birational geometry of rational surfaces and threefolds from the perspective of derived categories.

Algebraic Geometry · Mathematics 2023-11-28 Christian Böhning , Hans-Christian Graf von Bothmer , Yuri Tschinkel

We study the rationality of some geometrically rational three-dimensional conic and quadric surface bundles, defined over the reals and more general real closed fields, for which the real locus is connected and the intermediate Jacobian…

Algebraic Geometry · Mathematics 2026-04-22 Olivier Benoist , Alena Pirutka

We study the geometry of cuspidal $S_k$ singularities in $\mathbb R^3$ obtained by folding generically a cuspidal edge. In particular we study the geometry of the cuspidal cross-cap $M$, i.e. the cuspidal $S_0$ singularity. We study…

Differential Geometry · Mathematics 2017-12-18 Raúl Oset Sinha , Kentaro Saji

An equivariant stable birational invariant of an action of a finite group on a smooth projective variety is the first cohomology group of the Picard module. Bogomolov-Prokhorov and Shinder computed this for actions of cyclic groups on…

Algebraic Geometry · Mathematics 2022-03-04 Andrew Kresch , Yuri Tschinkel

We study the structure of combinatorial Burnside groups, which receive equivariant birational invariants of actions of finite groups on algebraic varieties.

Algebraic Geometry · Mathematics 2021-12-28 Yuri Tschinkel , Kaiqi Yang , Zhijia Zhang

In this note, we present a new look at translationally equivariant minimal Lagrangian surfaces in the complex projective plane via the loop group method.

Differential Geometry · Mathematics 2015-02-18 Josef F. Dorfmeister , Hui Ma

We classify combinations of isolated singularities that can occur on complex cubic threefolds generalizing analogous results for cubic surfaces due to Schl\"{a}fli and Bruce--Wall. In addition, we provide concise combinatorial description…

Algebraic Geometry · Mathematics 2024-05-07 Sasha Viktorova

We give a survey of the theory of finite quantum groupoids (weak Hopf algebras), including foundations of the theory and applications to finite depth subfactors, dynamical deformations of quantum groups, and invariants of knots and…

Quantum Algebra · Mathematics 2007-05-23 Dmitri Nikshych , Leonid Vainerman

In this paper, we first discuss cohomology and a one-parameter formal deformation theory of Lie-Yamaguti algebras. Next, we study finite group actions on Lie-Yamaguti algebras and introduce equivariant cohomology for Lie-Yamaguti algebras…

Rings and Algebras · Mathematics 2022-02-17 Shuangjian Guo , Bibhash Mondal , Ripan Saha

Let X be a projective complex 3-fold, quasihomogeneous with respect to an action of a linear algebraic group. We show that X is a compactification of SL_2/G, G a discrete subgroup, or that X can be equivariantly transformed into the 3-dim.…

Algebraic Geometry · Mathematics 2007-05-23 Stefan Kebekus

We investigate point-line geometries whose singular subspaces correspond to binary equidistant codes. The main result is a description of automorphisms of these geometries. In some important cases, automorphisms induced by non-monomial…

Combinatorics · Mathematics 2024-07-12 Mark Pankov , Krzysztof Petelczyc , Mariusz Zynel