13,228 research outputs found
Completeness of Flat Coalgebraic Fixpoint Logics
Modal fixpoint logics traditionally play a central role in computer science,
in particular in artificial intelligence and concurrency. The mu-calculus and
its relatives are among the most expressive logics of this type. However,
popular fixpoint logics tend to trade expressivity for simplicity and
readability, and in fact often live within the single variable fragment of the
mu-calculus. The family of such flat fixpoint logics includes, e.g., LTL, CTL,
and the logic of common knowledge. Extending this notion to the generic
semantic framework of coalgebraic logic enables covering a wide range of logics
beyond the standard mu-calculus including, e.g., flat fragments of the graded
mu-calculus and the alternating-time mu-calculus (such as alternating-time
temporal logic ATL), as well as probabilistic and monotone fixpoint logics. We
give a generic proof of completeness of the Kozen-Park axiomatization for such
flat coalgebraic fixpoint logics.Comment: Short version appeared in Proc. 21st International Conference on
Concurrency Theory, CONCUR 2010, Vol. 6269 of Lecture Notes in Computer
Science, Springer, 2010, pp. 524-53
Structure Theorems for Basic Algebras
A basic finite dimensional algebra over an algebraically closed field is
isomorphic to a quotient of a tensor algebra by an admissible ideal. The
category of left modules over the algebra is isomorphic to the category of
representations of a finite quiver with relations. In this article we will
remove the assumption that is algebraically closed to look at both perfect
and non-perfect fields. We will introduce the notion of species with relations
to describe the category of left modules over such algebras. If the field is
not perfect, then the algebra is isomorphic to a quotient of a tensor algebra
by an ideal that is no longer admissible in general. This gives hereditary
algebras isomorphic to a quotient of a tensor algebra by a non-zero ideal. We
will show that these non-zero ideals correspond to cyclic subgraphs of the
graph associated to the species of the algebra. This will lead to the ideal
being zero in the case when the underlying graph of the algebra is a tree
Decomposition spaces in combinatorics
A decomposition space (also called unital 2-Segal space) is a simplicial object satisfying an exactness condition weaker than the Segal condition: just as the Segal condition expresses (up to homotopy) composition, the new condition expresses decomposition. It is a general framework for incidence (co)algebras. In the present contribution, after establishing a formula for the section coefficients, we survey a large supply of examples, emphasising the notion's firm roots in classical combinatorics. The first batch of examples, similar to binomial posets, serves to illustrate two key points: (1) the incidence algebra in question is realised directly from a decomposition space, without a reduction step, and reductions are often given by CULF functors; (2) at the objective level, the convolution algebra is a monoidal structure of species. Specifically, we encounter the usual Cauchy product of species, the shuffle product of L-species, the Dirichlet product of arithmetic species, the Joyal-Street external product of q-species and the Morrison `Cauchy' product of q-species, and in each case a power series representation results from taking cardinality. The external product of q-species exemplifies the fact that Waldhausen's S-construction on an abelian category is a decomposition space, yielding Hall algebras. The next class of examples includes Schmitt's chromatic Hopf algebra, the Fa\`a di Bruno bialgebra, the Butcher-Connes-Kreimer Hopf algebra of trees and several variations from operad theory. Similar structures on posets and directed graphs exemplify a general construction of decomposition spaces from directed restriction species. We finish by computing the M\Preprin
Boundary Hamiltonian theory for gapped topological phases on an open surface
In this paper we propose a Hamiltonian approach to gapped topological phases
on an open surface with boundary. Our setting is an extension of the Levin-Wen
model to a 2d graph on the open surface, whose boundary is part of the graph.
We systematically construct a series of boundary Hamiltonians such that each of
them, when combined with the usual Levin-Wen bulk Hamiltonian, gives rise to a
gapped energy spectrum which is topologically protected; and the corresponding
wave functions are robust under changes of the underlying graph that maintain
the spatial topology of the system. We derive explicit ground-state
wavefunctions of the system and show that the boundary types are classified by
Morita-equivalent Frobenius algebras. We also construct boundary quasiparticle
creation, measuring and hopping operators. These operators allow us to
characterize the boundary quasiparticles by bimodules of Frobenius algebras.
Our approach also offers a concrete set of tools for computations. We
illustrate our approach by a few examples.Comment: 21 pages;references correcte
The Bisognano-Wichmann Theorem for Massive Theories
The geometric action of modular groups for wedge regions (Bisognano-Wichmann
property) is derived from the principles of local quantum physics for a large
class of Poincare covariant models in d=4. As a consequence, the CPT theorem
holds for this class. The models must have a complete interpretation in terms
of massive particles. The corresponding charges need not be localizable in
compact regions: The most general case is admitted, namely localization in
spacelike cones.Comment: 16 pages; improved and corrected formulation
Matrix product and sum rule for Macdonald polynomials
We present a new, explicit sum formula for symmetric Macdonald polynomials
and show that they can be written as a trace over a product of
(infinite dimensional) matrices. These matrices satisfy the
Zamolodchikov--Faddeev (ZF) algebra. We construct solutions of the ZF algebra
from a rank-reduced version of the Yang--Baxter algebra. As a corollary, we
find that the normalization of the stationary measure of the multi-species
asymmetric exclusion process is a Macdonald polynomial with all variables set
equal to one.Comment: 11 pages, extended abstract submission to FPSA
A multi-species asymmetric simple exclusion process and its relation to traffic flow
Using the matrix product formalism we formulate a natural p-species
generalization of the asymmetric simple exclusion process. In this model
particles hop with their own specific rate and fast particles can overtake slow
ones with a rate equal to their relative speed. We obtain the algebraic
structure and study the properties of the representations in detail. The
uncorrelated steady state for the open system is obtained and in the ( limit, the dependence of its characteristics on the distribution of
velocities is determined. It is shown that when the total arrival rate of
particles exceeds a certain value, the density of the slowest particles rises
abroptly.Comment: some typos corrected, references adde
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