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To study a noncompact Riemannian manifold, it is often useful to find a compactification. We discuss several common compactifications and survey some recent results.

Differential Geometry · Mathematics 2010-12-15 Xiaodong Wang

The A-hierarchy is a parametric analogue of the polynomial hierarchy in the context of paramterised complexity theory. We give a new characterisation of the A-hierarchy in terms of a generalisation of the SUBSET-SUM problem.

Logic in Computer Science · Computer Science 2024-09-13 Jan Gutleben , Arne Meier

In a bicategory of spans (an example of a 'generic bicategory') the factorization of a span (s,t) as the span (s,1) followed by (1,t) satisfies a simple universal property with respect to all factorizations in terms of the generic…

Category Theory · Mathematics 2020-02-25 Charles Walker

A finite-dimensional unital and associative algebra over $\mathbb{R}$, or what we shall call simply "an algebra" in this paper for short, generalities the construction by which we derive the complex numbers by "adjoining an element $i$" to…

Rings and Algebras · Mathematics 2017-08-04 Nathan BeDell

An important ingredient in the completion theorem of equivariant K-theory given by S. Jackowski is that the representation ring R(Gamma) of a compact Lie group satisfies two restriction properties called (N) and (R\_{F}). We give in this…

Algebraic Topology · Mathematics 2007-05-23 Abdelouahab Arouche

Given a variety of universal algebras. A method is suggested for describing automorphisms of a category of free algebras of this variety. Applying this general method all automorphisms of such categories are found in two cases: 1) for the…

Rings and Algebras · Mathematics 2007-05-23 Boris Plotkin , Grigori Zhitomirski

Orthogonal spaces are vector spaces together with a quadratic form whose associated bilinear form is non-degenerate. Over fields of characteristic two, there are many quadratic forms associated to a given bilinear form and quadratic…

Logic · Mathematics 2024-08-20 Charlotte Kestner , Nicholas Ramsey

We develop a theory of nearby and vanishing cycles in the context of finite-coefficient Zariski-constructible sheaves over a non-archimedean field which is non-trivially valued, complete, algebraically closed, and of mixed characteristic or…

Algebraic Geometry · Mathematics 2025-04-24 Tong Zhou

We consider compatibility conditions between Poisson and Riemannian structures on smooth manifolds by means of a contravariant partially complex structure, or $f$-structure, introducing the notion of (almost) K\"ahler--Poisson manifolds. In…

Symplectic Geometry · Mathematics 2017-09-11 Nicolás Martínez Alba , Andrés Vargas

For a generic set in the Teichmueller space, we construct a covariant functor with the range in a category of the AF-algebras; the functor maps isomorphic Riemann surfaces to the stably isomorphic AF-algebras. As a special case, one gets a…

Operator Algebras · Mathematics 2016-06-08 Igor Nikolaev

In this paper, we define and study (co)homology theories of a compatible associative algebra $A$. At first, we construct a new graded Lie algebra whose Maurer-Cartan elements are given by compatible associative structures. Then we define…

Rings and Algebras · Mathematics 2021-07-21 Taoufik Chtioui , Apurba Das , Sami Mabrouk

We introduce the coherent algebra of a compact metric measure space by analogy with the corresponding concept for a finite graph. As an application we show that upon topologizing the collection of isomorphism classes of compact metric…

Operator Algebras · Mathematics 2018-12-04 Alexandru Chirvasitu

We study differential forms on the universal vector extension $A^\natural$ of an abelian scheme $A$ in characteristic zero, and derive a new construction of the $D$-group scheme structure on $A^\natural$. This gives, in particular, a rather…

Algebraic Geometry · Mathematics 2022-03-11 Tiago J. Fonseca , Nils Matthes

We make an attempt to develop "noncommutative algebraic geometry" in which noncommutative affine schemes are in one-to-one correspondence with associative algebras. In the first part we discuss various aspects of smoothness in affine…

Algebraic Geometry · Mathematics 2016-09-07 Maxim Kontsevich , Alexander Rosenberg

We introduce W-spin structures on a Riemann surface and give a precise definition to the corresponding W-spin equations for any quasi-homogeneous polynomial W. Then, we construct examples of nonzero solutions of spin equations in the…

Differential Geometry · Mathematics 2008-02-23 Huijun Fan , Tyler J. Jarvis , Yongbin Ruan

We study varieties $\mathcal{A}_n$ arising as equivariant compactifications of the space of $n$ points in $\mathbb{C}$ up to overall translation. We define $\mathcal{A}_n$ and examine its basic geometric properties before constructing an…

Algebraic Geometry · Mathematics 2024-03-26 Antonios-Alexandros Robotis

Given an associative algebra H, a linear space U and some linear maps J, T, \gamma , \eta satisfying some axioms, we define an associative algebra structure on U\otimes H, called an L-R-crossed product. This contains as particular cases…

Quantum Algebra · Mathematics 2024-10-14 Florin Panaite

A completeness conjecture is advanced concerning the free small-colimit completion P(A) of a (possibly large) category A. The conjecture is based on the existence of a small generating-cogenerating set of objects in A. We sketch how the…

Category Theory · Mathematics 2009-09-29 Brian J. Day

In this paper we prove a compactness theorem for a sequence of harmonic maps which are defined on a converging sequence of Riemannian manifolds.

Differential Geometry · Mathematics 2014-12-02 Zahra Sinaei

Let F be a global field, and let S be a finite set of places of F containing all archimedean places. Consider the product X of the symmetric spaces and Bruhat-Tits buildings for PGL_d of the completions of F at archimedean and…

Number Theory · Mathematics 2016-12-12 Takako Fukaya , Kazuya Kato , Romyar Sharifi