3,948 research outputs found
A density functional theory for general hard-core lattice gases
We put forward a general procedure to obtain an approximate free energy
density functional for any hard-core lattice gas, regardless of the shape of
the particles, the underlying lattice or the dimension of the system. The
procedure is conceptually very simple and recovers effortlessly previous
results for some particular systems. Also, the obtained density functionals
belong to the class of fundamental measure functionals and, therefore, are
always consistent through dimensional reduction. We discuss possible extensions
of this method to account for attractive lattice models.Comment: 4 pages, 1 eps figure, uses RevTeX
The Hilbert space of Chern-Simons theory on the cylinder. A Loop Quantum Gravity approach
As a laboratory for loop quantum gravity, we consider the canonical
quantization of the three-dimensional Chern-Simons theory on a noncompact space
with the topology of a cylinder. Working within the loop quantization
formalism, we define at the quantum level the constraints appearing in the
canonical approach and completely solve them, thus constructing a gauge and
diffeomorphism invariant physical Hilbert space for the theory. This space
turns out to be infinite dimensional, but separable.Comment: Minor changes and some references added. Latex, 16 pages, 1 figur
Differential Calculus on Graphon Space
Recently, the theory of dense graph limits has received attention from
multiple disciplines including graph theory, computer science, statistical
physics, probability, statistics, and group theory. In this paper we initiate
the study of the general structure of differentiable graphon parameters . We
derive consistency conditions among the higher G\^ateaux derivatives of
when restricted to the subspace of edge weighted graphs .
Surprisingly, these constraints are rigid enough to imply that the multilinear
functionals satisfying the
constraints are determined by a finite set of constants indexed by isomorphism
classes of multigraphs with edges and no isolated vertices. Using this
structure theory, we explain the central role that homomorphism densities play
in the analysis of graphons, by way of a new combinatorial interpretation of
their derivatives. In particular, homomorphism densities serve as the monomials
in a polynomial algebra that can be used to approximate differential graphon
parameters as Taylor polynomials. These ideas are summarized by our main
theorem, which asserts that homomorphism densities where has at
most edges form a basis for the space of smooth graphon parameters whose
st derivatives vanish. As a consequence of this theory, we also extend
and derive new proofs of linear independence of multigraph homomorphism
densities, and characterize homomorphism densities. In addition, we develop a
theory of series expansions, including Taylor's theorem for graph parameters
and a uniqueness principle for series. We use this theory to analyze questions
raised by Lov\'asz, including studying infinite quantum algebras and the
connection between right- and left-homomorphism densities.Comment: Final version (36 pages), accepted for publication in Journal of
Combinatorial Theory, Series
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