Expand all Collapse all | Results 1 - 19 of 19 |
1. CMB Online first
Classification of Integral Modular Categories of Frobenius--Perron Dimension $pq^4$ and $p^2q^2$ We classify integral modular categories of dimension $pq^4$ and $p^2q^2$,
where
$p$ and $q$ are distinct primes. We show that such categories are always
group-theoretical except for categories of dimension $4q^2$.
In these cases there are
well-known examples of non-group-theoretical categories, coming from
centers of
Tambara-Yamagami categories and quantum groups. We show that a
non-group-theoretical integral modular category of dimension $4q^2$ is
equivalent to either one of these well-known examples or is of dimension
$36$ and is twist-equivalent to fusion categories arising from a
certain quantum group.
Keywords:modular categories, fusion categories Category:18D10 |
2. CMB 2013 (vol 57 pp. 318)
Duality of Preenvelopes and Pure Injective Modules Let $R$ be an arbitrary ring and $(-)^+=\operatorname{Hom}_{\mathbb{Z}}(-,
\mathbb{Q}/\mathbb{Z})$ where $\mathbb{Z}$ is the ring of integers
and $\mathbb{Q}$ is the ring of rational numbers, and let
$\mathcal{C}$ be a subcategory of left $R$-modules and $\mathcal{D}$
a subcategory of right $R$-modules such that $X^+\in \mathcal{D}$
for any $X\in \mathcal{C}$ and all modules in $\mathcal{C}$ are pure
injective. Then a homomorphism $f: A\to C$ of left $R$-modules with
$C\in \mathcal{C}$ is a $\mathcal{C}$-(pre)envelope of $A$ provided
$f^+: C^+\to A^+$ is a $\mathcal{D}$-(pre)cover of $A^+$. Some
applications of this result are given.
Keywords:(pre)envelopes, (pre)covers, duality, pure injective modules, character modules Categories:18G25, 16E30 |
3. CMB Online first
On Braided and Ribbon Unitary Fusion Categories We prove that every braiding over a unitary fusion category is
unitary and every unitary braided fusion category admits a unique
unitary ribbon structure.
Keywords:fusion categories, braided categories, modular categories Categories:20F36, 16W30, 18D10 |
4. CMB 2011 (vol 55 pp. 319)
The Verdier Hypercovering Theorem This note gives a simple cocycle-theoretic proof of the Verdier
hypercovering theorem. This theorem approximates morphisms $[X,Y]$ in the
homotopy category of simplicial sheaves or presheaves by simplicial
homotopy classes of maps, in the case where $Y$ is locally fibrant. The
statement proved in this paper is a generalization of the standard
Verdier hypercovering result in that it is pointed (in a very broad
sense) and there is no requirement for the source object $X$ to be
locally fibrant.
Keywords:simplicial presheaf, hypercover, cocycle Categories:14F35, 18G30, 55U35 |
5. CMB 2010 (vol 53 pp. 425)
Free Pre-Lie Algebras are Free as Lie Algebras We prove that the $\mathfrak{S}$-module $\operatorname{PreLie}$ is a free Lie algebra in
the category of $\mathfrak{S}$-modules and can therefore be written as the
composition of the $\mathfrak{S}$-module $\operatorname{Lie}$ with a new $\mathfrak{S}$-module
$X$. This implies that free pre-Lie algebras in the category of
vector spaces, when considered as Lie algebras, are free on
generators that can be described using $X$. Furthermore, we define a
natural filtration on the $\mathfrak{S}$-module $X$. We also obtain a
relationship between $X$ and the $\mathfrak{S}$-module coming from the
anticyclic structure of the $\operatorname{PreLie}$ operad.
Categories:18D50, 17B01, 18G40, 05C05 |
6. CMB 2009 (vol 52 pp. 273)
Amalgamations of Categories We consider the pushout of embedding functors in $\Cat$, the
category of small categories.
We show that if the embedding functors satisfy a 3-for-2
property, then the induced functors to the pushout category are
also embeddings. The result follows from the connectedness of
certain associated slice categories. The condition is motivated
by a similar result for maps of semigroups. We show that our
theorem can be applied to groupoids and to inclusions of full
subcategories. We also give an example to show that the theorem
does not hold when the
property only holds for one of the inclusion functors, or when it
is weakened to a one-sided condition.
Keywords:category, pushout, amalgamation Categories:18A30, 18B40, 20L17 |
7. CMB 2008 (vol 51 pp. 310)
Relative Homotopy in Relational Structures The homotopy groups of a finite partially ordered set (poset) can be
described entirely in the context of posets, as shown in a paper by
B. Larose and C. Tardif.
In this paper we describe the relative version of such a
homotopy theory, for pairs $(X,A)$ where $X$ is a poset and $A$ is a
subposet of $X$. We also prove some theorems on the relevant version
of the notion of weak homotopy equivalences for maps of pairs of such
objects. We work in the category of reflexive binary relational
structures which contains the posets as in the work of Larose and
Tardif.
Keywords:binary reflexive relational structure, relative homotopy group, exact sequence, locally finite space, weak homotopy equivalence Categories:55Q05, 54A05;, 18B30 |
8. CMB 2008 (vol 51 pp. 81)
Homotopy Formulas for Cyclic Groups Acting on Rings The positive cohomology groups of a finite group acting on a ring
vanish when the ring has a norm one element. In this note we give
explicit homotopies on the level of cochains when the group is cyclic,
which allows us to express any cocycle of a cyclic group
as the coboundary of an explicit cochain.
The formulas in this note are closely related to the effective problems considered in previous joint work
with Eli Aljadeff.
Keywords:group cohomology, norm map, cyclic group, homotopy Categories:20J06, 20K01, 16W22, 18G35 |
9. CMB 2007 (vol 50 pp. 440)
A KÃ¼nneth Theorem for $p$-Adic Groups Let $G_1$ and $G_2$ be $p$-adic groups. We describe a decomposition of
${\rm Ext}$-groups in the category of smooth representations of
$G_1 \times G_2$ in terms of ${\rm Ext}$-groups for $G_1$ and $G_2$.
We comment on ${\rm Ext}^1_G(\pi,\pi)$ for a supercuspidal
representation
$\pi$ of a $p$-adic group $G$. We also consider an example of
identifying
the class, in a suitable ${\rm Ext}^1$, of a Jacquet module of certain
representations of $p$-adic ${\rm GL}_{2n}$.
Categories:22E50, 18G15, 55U25 |
10. CMB 2007 (vol 50 pp. 182)
On the Coxeter Transformations for Tamari Posets A relation between the anticyclic structure of the dendriform operad
and the Coxeter transformations in the Grothendieck groups of the
derived categories of modules over the Tamari posets is obtained.
Categories:18D50, 18E30, 06A11 |
11. CMB 2006 (vol 49 pp. 407)
Intermediate Model Structures for Simplicial Presheaves This note shows that any set of cofibrations containing the standard
set of generating projective cofibrations determines a cofibrantly
generated proper closed model structure on the category of simplicial
presheaves on a small Grothendieck site, for which the weak
equivalences are the local weak equivalences in the usual sense.
Categories:18G30, 18F20, 55U35 |
12. CMB 2004 (vol 47 pp. 321)
Classifying Spaces for Monoidal Categories Through Geometric Nerves The usual constructions of classifying spaces for monoidal categories
produce CW-complexes with
many cells that, moreover, do not have any proper geometric meaning.
However, geometric nerves of
monoidal categories are very handy simplicial sets whose simplices
have
a pleasing geometric
description: they are diagrams with the shape of the 2-skeleton of
oriented standard simplices. The
purpose of this paper is to prove that geometric realizations of
geometric nerves are classifying
spaces for monoidal categories.
Keywords:monoidal category, pseudo-simplicial category,, simplicial set, classifying space, homotopy type Categories:18D10, 18G30, 55P15, 55P35, 55U40 |
13. CMB 2003 (vol 46 pp. 429)
The Grothendieck Trace and the de Rham Integral On a smooth $n$-dimensional complete variety $X$ over ${\mathbb C}$ we
show that the trace map ${\tilde\theta}_X \colon\break
H^n (X,\Omega_X^n)
\to {\mathbb C}$ arising from Lipman's version of Grothendieck duality
in \cite{ast-117} agrees with
$$
(2\pi i)^{-n} (-1)^{n(n-1)/2} \int_X \colon H^{2n}_{DR} (X,{\mathbb
C}) \to {\mathbb C}
$$
under the Dolbeault isomorphism.
Categories:14F10, 32A25, 14A15, 14F05, 18E30 |
14. CMB 2002 (vol 45 pp. 180)
On the Exponent of the ${\nk}_0$-Groups of Virtually Infinite Cyclic Groups It is known that the $K$-theory of a large class of groups can be
computed from the $K$-theory of their virtually infinite cyclic
subgroups. On the other hand, Nil-groups appear to be the obstacle in
calculations involving the $K$-theory of the latter. The main
difficulty in the calculation of Nil-groups is that they are
infinitely generated when they do not vanish. We develop methods for
computing the exponent of ${\nk}_0$-groups that appear in the
calculation of the $K_0$-groups of virtually infinite cyclic groups.
Categories:18F25, 19A31 |
15. CMB 2001 (vol 44 pp. 459)
LS-catÃ©gorie algÃ©brique et attachement de cellules Nous montrons que la A-cat\'egorie d'un espace simplement connexe de
type fini est inf\'erieure ou \'egale \`a $n$ si et seulement si son
mod\`ele d'Adams-Hilton est un r\'etracte homotopique d'une alg\`ebre
diff\'erentielle \`a $n$ \'etages. Nous en d\'eduisons que
l'invariant $\Acat$ augmente au plus de 1 lors de l'attachement
d'une cellule \`a un espace.
We show that the A-category of a simply connected space of finite type
is less than or equal to $n$ if and only if its Adams-Hilton model is
a homotopy retract of an $n$-stage differential algebra. We deduce
from this that the invariant $\Acat$ increases by at most 1 when a
cell is attached to a space.
Keywords:LS-category, strong category, Adams-Hilton models, cell attachments Categories:55M30, 18G55 |
16. CMB 2000 (vol 43 pp. 138)
Exponential Laws for the Nachbin Ported Topology We show that for $U$ and $V$ balanced open subsets of (Qno) Fr\'echet
spaces $E$ and $F$ that we have the topological identity
$$
\bigl( {\cal H}(U\times V), \tau_\omega \bigr) = \biggl( {\cal H}
\Bigl( U; \bigl( {\cal H}(V), \tau_\omega \bigr) \Bigr), \tau_\omega
\biggr).
$$
Analogous results for the compact open topology have long been
established. We also give an example to show that the (Qno)
hypothesis on both $E$ and $F$ is necessary.
Categories:46G20, 18D15, 46M05 |
17. CMB 2000 (vol 43 pp. 162)
Moduli Spaces of Polygons and Punctured Riemann Spheres The purpose of this note is to give a simple combinatorial
construction of the map from the canonically compactified moduli
spaces of punctured complex projective lines to the moduli spaces
$\P_r$ of polygons with fixed side lengths in the Euclidean space
$\E^3$. The advantage of this construction is that one can obtain a
complete set of linear relations among the cycles that generate
homology of $\P_r$. We also classify moduli spaces of pentagons.
Categories:14D20, 18G55, 14H10 |
18. CMB 2000 (vol 43 pp. 3)
Resolutions of Associative and Lie Algebras Certain canonical resolutions are described for free associative and
free Lie algebras in the category of non-associative algebras. These
resolutions derive in both cases from geometric objects, which in turn
reflect the combinatorics of suitable collections of leaf-labeled
trees.
Keywords:resolutions, homology, Lie algebras, associative algebras, non-associative algebras, Jacobi identity, leaf-labeled trees, associahedron Categories:18G10, 05C05, 16S10, 17B01, 17A50, 18G50 |
19. CMB 1997 (vol 40 pp. 39)
On projective $Z$-frames This paper deals with the projective objects in the category of all
$Z$-frames, where the latter is a common generalization of
different types of frames. The main result obtained here is that a
$Z$-frame is ${\bf E}$-projective if and only if it is stably
$Z$-continuous, for a naturally arising collection ${\bf E}$ of morphisms.
Categories:06D05, 54D10, 18D15 |