64 research outputs found
A description of a class of finite semigroups that are near to being Malcev nilpotent
In this paper we continue the investigations on the algebraic structure of a
finite semigroup that is determined by its associated upper non-nilpotent
graph . The vertices of this graph are the elements of and
two vertices are adjacent if they generate a semigroup that is not nilpotent
(in the sense of Malcev). We introduce a class of semigroups in which the
Mal'cev nilpotent property lifts through ideal chains. We call this the class
of \B\ semigroups. The definition is such that the global information that a
semigroup is not nilpotent induces local information, i.e. some two-generated
subsemigroups are not nilpotent. It turns out that a finite monoid (in
particular, a finite group) is \B\ if and only if it is nilpotent. Our main
result is a description of \B\ finite semigroups in terms of their
associated graph . In particular, has a largest nilpotent
ideal, say , and is a 0-disjoint union of its connected components
(adjoined with a zero) with at least two elements
Finite nilpotent semigroups of small coclass
The parameter coclass has been used successfully in the study of nilpotent
algebraic objects of different kinds. In this paper a definition of coclass for
nilpotent semigroups is introduced and semigroups of coclass 0, 1, and 2 are
classified. Presentations for all such semigroups and formulae for their
numbers are obtained. The classification is provided up to isomorphism as well
as up to isomorphism or anti-isomorphism. Commutative and self-dual semigroups
are identified within the classification.Comment: 11 page
Hyperk\"ahler torsion structures invariant by nilpotent Lie groups
We study HKT structures on nilpotent Lie groups and on associated
nilmanifolds. We exhibit three weak HKT structures on which are
homogeneous with respect to extensions of Heisenberg type Lie groups. The
corresponding hypercomplex structures are of a special kind, called abelian. We
prove that on any 2-step nilpotent Lie group all invariant HKT structures arise
from abelian hypercomplex structures. Furthermore, we use a correspondence
between abelian hypercomplex structures and subspaces of to
produce continuous families of compact and noncompact of manifolds carrying non
isometric HKT structures. Finally, geometrical properties of invariant HKT
structures on 2-step nilpotent Lie groups are obtained.Comment: LateX, 12 page
Global behavior of solutions to the static spherically symmetric EYM equations
The set of all possible spherically symmetric magnetic static
Einstein-Yang-Mills field equations for an arbitrary compact semi-simple gauge
group was classified in two previous papers. Local analytic solutions near
the center and a black hole horizon as well as those that are analytic and
bounded near infinity were shown to exist. Some globally bounded solutions are
also known to exist because they can be obtained by embedding solutions for the
case which is well understood. Here we derive some asymptotic
properties of an arbitrary global solution, namely one that exists locally near
a radial value , has positive mass at and develops no
horizon for all . The set of asymptotic values of the Yang-Mills
potential (in a suitable well defined gauge) is shown to be finite in the
so-called regular case, but may form a more complicated real variety for models
obtained from irregular rotation group actions.Comment: 43 page
Smooth Loops and Fiber Bundles: Theory of Principal Q-bundles
A nonassociative generalization of the principal fiber bundles with a smooth
loop mapping on the fiber is presented. Our approach allows us to construct a
new kind of gauge theories that involve higher ''nonassociative'' symmetries.Comment: 20 page
Uniformity in the Wiener-Wintner theorem for nilsequences
We prove a uniform extension of the Wiener-Wintner theorem for nilsequences
due to Host and Kra and a nilsequence extension of the topological
Wiener-Wintner theorem due to Assani. Our argument is based on (vertical)
Fourier analysis and a Sobolev embedding theorem.Comment: v3: 18 p., proof that the cube construction produces compact
homogeneous spaces added, measurability issues in the proof of Theorem 1.5
addressed. We thank the anonymous referees for pointing out these gaps in v
Sufficient conditions for the strong stability of linear canonical systems with periodic coefficients
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