988 research outputs found
Dirichlet sigma models and mean curvature flow
The mean curvature flow describes the parabolic deformation of embedded
branes in Riemannian geometry driven by their extrinsic mean curvature vector,
which is typically associated to surface tension forces. It is the gradient
flow of the area functional, and, as such, it is naturally identified with the
boundary renormalization group equation of Dirichlet sigma models away from
conformality, to lowest order in perturbation theory. D-branes appear as fixed
points of this flow having conformally invariant boundary conditions. Simple
running solutions include the paper-clip and the hair-pin (or grim-reaper)
models on the plane, as well as scaling solutions associated to rational (p, q)
closed curves and the decay of two intersecting lines. Stability analysis is
performed in several cases while searching for transitions among different
brane configurations. The combination of Ricci with the mean curvature flow is
examined in detail together with several explicit examples of deforming curves
on curved backgrounds. Some general aspects of the mean curvature flow in
higher dimensional ambient spaces are also discussed and obtain consistent
truncations to lower dimensional systems. Selected physical applications are
mentioned in the text, including tachyon condensation in open string theory and
the resistive diffusion of force-free fields in magneto-hydrodynamics.Comment: 77 pages, 21 figure
The calculus of multivectors on noncommutative jet spaces
The Leibniz rule for derivations is invariant under cyclic permutations of
co-multiples within the arguments of derivations. We explore the implications
of this principle: in effect, we construct a class of noncommutative bundles in
which the sheaves of algebras of walks along a tesselated affine manifold form
the base, whereas the fibres are free associative algebras or, at a later
stage, such algebras quotients over the linear relation of equivalence under
cyclic shifts. The calculus of variations is developed on the infinite jet
spaces over such noncommutative bundles.
In the frames of such field-theoretic extension of the Kontsevich formal
noncommutative symplectic (super)geometry, we prove the main properties of the
Batalin--Vilkovisky Laplacian and Schouten bracket. We show as by-product that
the structures which arise in the classical variational Poisson geometry of
infinite-dimensional integrable systems do actually not refer to the graded
commutativity assumption.Comment: Talks given at Mathematics seminar (IHES, 25.11.2016) and Oberseminar
(MPIM Bonn, 2.02.2017), 23 figures, 60 page
Four out-of-equilibrium lectures
A collection of published papers on the subject of classical nonequilibrium statistical mechanics. Mainly stochastic systems are considered, with special regard to applications in soft matter physic
Anonymous Point Collection - Improved Models and Security Definitions
This work is a comprehensive, formal treatment of anonymous point collection. The proposed definition does not only provide a strong notion of security and privacy, but also covers features which are important for practical use. An efficient realization is presented and proven to fulfill the proposed definition. The resulting building block is the first one that allows for anonymous two-way transactions, has semi-offline capabilities, yields constant storage size, and is provably secure
Multicoloured Random Graphs: Constructions and Symmetry
This is a research monograph on constructions of and group actions on
countable homogeneous graphs, concentrating particularly on the simple random
graph and its edge-coloured variants. We study various aspects of the graphs,
but the emphasis is on understanding those groups that are supported by these
graphs together with links with other structures such as lattices, topologies
and filters, rings and algebras, metric spaces, sets and models, Moufang loops
and monoids. The large amount of background material included serves as an
introduction to the theories that are used to produce the new results. The
large number of references should help in making this a resource for anyone
interested in beginning research in this or allied fields.Comment: Index added in v2. This is the first of 3 documents; the other 2 will
appear in physic
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