Quiver Grassmannians of Extended Dynkin Type D Part I: Schubert Systems and Decompositions into Affine Spaces

Quiver Grassmannians of Extended Dynkin Type D Part I: Schubert Systems and Decompositions into Affine Spaces
Author: Oliver Lorscheid
Publisher: American Mathematical Soc.
Total Pages: 90
Release: 2019-12-02
Genre: Education
ISBN: 1470436477

Let Q be a quiver of extended Dynkin type D˜n. In this first of two papers, the authors show that the quiver Grassmannian Gre–(M) has a decomposition into affine spaces for every dimension vector e– and every indecomposable representation M of defect −1 and defect 0, with the exception of the non-Schurian representations in homogeneous tubes. The authors characterize the affine spaces in terms of the combinatorics of a fixed coefficient quiver for M. The method of proof is to exhibit explicit equations for the Schubert cells of Gre–(M) and to solve this system of equations successively in linear terms. This leads to an intricate combinatorial problem, for whose solution the authors develop the theory of Schubert systems. In Part 2 of this pair of papers, they extend the result of this paper to all indecomposable representations M of Q and determine explicit formulae for the F-polynomial of M.

Representation Theory and Beyond

Representation Theory and Beyond
Author: Jan Šťovíček
Publisher: American Mathematical Soc.
Total Pages: 298
Release: 2020-11-13
Genre: Education
ISBN: 147045131X

This volume contains the proceedings of the Workshop and 18th International Conference on Representations of Algebras (ICRA 2018) held from August 8–17, 2018, in Prague, Czech Republic. It presents several themes of contemporary representation theory together with some new tools, such as stable ∞ ∞-categories, stable derivators, and contramodules. In the first part, expanded lecture notes of four courses delivered at the workshop are presented, covering the representation theory of finite sets with correspondences, geometric theory of quiver Grassmannians, recent applications of contramodules to tilting theory, as well as symmetries in the representation theory over an abstract stable homotopy theory. The second part consists of six more-advanced papers based on plenary talks of the conference, presenting selected topics from contemporary representation theory: recollements and purity, maximal green sequences, cohomological Hall algebras, Hochschild cohomology of associative algebras, cohomology of local selfinjective algebras, and the higher Auslander–Reiten theory studied via homotopy theory.

Quiver Grassmannians of Extended Dynkin Type D.

Quiver Grassmannians of Extended Dynkin Type D.
Author: Oliver Lorscheid
Publisher:
Total Pages: 78
Release: 2019
Genre: Electronic books
ISBN: 9781470453992

Let Q be a quiver of extended Dynkin type \widetildeD}_n. In this first of two papers, the authors show that the quiver Grassmannian \mathrmGr}_{underline{e}}(M) has a decomposition into affine spaces for every dimension vector underlinee} and every indecomposable representation M of defect -1 and defect 0, with the exception of the non-Schurian representations in homogeneous tubes. The authors characterize the affine spaces in terms of the combinatorics of a fixed coefficient quiver for M. The method of proof is to exhibit explicit equations for the Schubert cells of \mathrmGr}_{underline{e}}(M) and to solve this system of equations successively in linear terms. This leads to an intricate combinatorial problem, for whose solution the authors develop the theory of Schubert systems. In Part 2 of this pair of papers, they extend the result of this paper to all indecomposable representations M of Q and determine explicit formulae for the F-polynomial of M.

Automorphisms of Fusion Systems of Finite Simple Groups of Lie Type

Automorphisms of Fusion Systems of Finite Simple Groups of Lie Type
Author: Carles Broto
Publisher: American Mathematical Soc.
Total Pages: 176
Release: 2020-02-13
Genre: Education
ISBN: 1470437724

For a finite group G of Lie type and a prime p, the authors compare the automorphism groups of the fusion and linking systems of G at p with the automorphism group of G itself. When p is the defining characteristic of G, they are all isomorphic, with a very short list of exceptions. When p is different from the defining characteristic, the situation is much more complex but can always be reduced to a case where the natural map from Out(G) to outer automorphisms of the fusion or linking system is split surjective. This work is motivated in part by questions involving extending the local structure of a group by a group of automorphisms, and in part by wanting to describe self homotopy equivalences of BG∧p in terms of Out(G).

Affine Flag Varieties and Quantum Symmetric Pairs

Affine Flag Varieties and Quantum Symmetric Pairs
Author: Zhaobing Fan
Publisher: American Mathematical Soc.
Total Pages: 123
Release: 2020-09-28
Genre: Mathematics
ISBN: 1470441756

The quantum groups of finite and affine type $A$ admit geometric realizations in terms of partial flag varieties of finite and affine type $A$. Recently, the quantum group associated to partial flag varieties of finite type $B/C$ is shown to be a coideal subalgebra of the quantum group of finite type $A$.

Degree Theory of Immersed Hypersurfaces

Degree Theory of Immersed Hypersurfaces
Author: Harold Rosenberg
Publisher: American Mathematical Soc.
Total Pages: 62
Release: 2020-09-28
Genre: Mathematics
ISBN: 1470441853

The authors develop a degree theory for compact immersed hypersurfaces of prescribed $K$-curvature immersed in a compact, orientable Riemannian manifold, where $K$ is any elliptic curvature function.

Subgroup Decomposition in Out(Fn)

Subgroup Decomposition in Out(Fn)
Author: Michael Handel
Publisher: American Mathematical Soc.
Total Pages: 290
Release: 2020-05-13
Genre: Education
ISBN: 1470441136

In this work the authors develop a decomposition theory for subgroups of Out(Fn) which generalizes the decomposition theory for individual elements of Out(Fn) found in the work of Bestvina, Feighn, and Handel, and which is analogous to the decomposition theory for subgroups of mapping class groups found in the work of Ivanov.

The Triangle-Free Process and the Ramsey Number R(3,k)

The Triangle-Free Process and the Ramsey Number R(3,k)
Author: Gonzalo Fiz Pontiveros
Publisher: American Mathematical Soc.
Total Pages: 138
Release: 2020-04-03
Genre: Education
ISBN: 1470440717

The areas of Ramsey theory and random graphs have been closely linked ever since Erdős's famous proof in 1947 that the “diagonal” Ramsey numbers R(k) grow exponentially in k. In the early 1990s, the triangle-free process was introduced as a model which might potentially provide good lower bounds for the “off-diagonal” Ramsey numbers R(3,k). In this model, edges of Kn are introduced one-by-one at random and added to the graph if they do not create a triangle; the resulting final (random) graph is denoted Gn,△. In 2009, Bohman succeeded in following this process for a positive fraction of its duration, and thus obtained a second proof of Kim's celebrated result that R(3,k)=Θ(k2/logk). In this paper the authors improve the results of both Bohman and Kim and follow the triangle-free process all the way to its asymptotic end.

Global Well-Posedness of High Dimensional Maxwell–Dirac for Small Critical Data

Global Well-Posedness of High Dimensional Maxwell–Dirac for Small Critical Data
Author: Cristian Gavrus
Publisher: American Mathematical Soc.
Total Pages: 106
Release: 2020-05-13
Genre: Education
ISBN: 147044111X

In this paper, the authors prove global well-posedness of the massless Maxwell–Dirac equation in the Coulomb gauge on R1+d(d≥4) for data with small scale-critical Sobolev norm, as well as modified scattering of the solutions. Main components of the authors' proof are A) uncovering null structure of Maxwell–Dirac in the Coulomb gauge, and B) proving solvability of the underlying covariant Dirac equation. A key step for achieving both is to exploit (and justify) a deep analogy between Maxwell–Dirac and Maxwell-Klein-Gordon (for which an analogous result was proved earlier by Krieger-Sterbenz-Tataru, which says that the most difficult part of Maxwell–Dirac takes essentially the same form as Maxwell-Klein-Gordon.