1,511 research outputs found
Holographic Special Relativity
We reinterpret special relativity, or more precisely its de Sitter
deformation, in terms of 3d conformal geometry, as opposed to (3+1)d spacetime
geometry. An inertial observer, usually described by a geodesic in spacetime,
becomes instead a choice of ways to reverse the conformal compactification of a
Euclidean vector space up to scale. The observer's "current time," usually
given by a point along the geodesic, corresponds to the choice of scale in the
decompactification. We also show how arbitrary conformal 3-geometries give rise
to "observer space geometries," as defined in recent work, from which spacetime
can be reconstructed under certain integrability conditions. We conjecture a
relationship between this kind of "holographic relativity" and the "shape
dynamics" proposal of Barbour and collaborators, in which conformal space takes
the place of spacetime in general relativity. We also briefly survey related
pictures of observer space, including the AdS analog and a representation
related to twistor theory.Comment: 17 pages, 5 illustration
On the ultraviolet behaviour of quantum fields over noncommutative manifolds
By exploiting the relation between Fredholm modules and the
Segal-Shale-Stinespring version of canonical quantization, and taking as
starting point the first-quantized fields described by Connes' axioms for
noncommutative spin geometries, a Hamiltonian framework for fermion quantum
fields over noncommutative manifolds is introduced. We analyze the ultraviolet
behaviour of second-quantized fields over noncommutative 3-tori, and discuss
what behaviour should be expected on other noncommutative spin manifolds.Comment: 10 pages, RevTeX version, a few references adde
Relative Affine Structure: Canonical Model for 3D from 2D Geometry and Applications
We propose an affine framework for perspective views, captured by a single extremely simple equation based on a viewer-centered invariant we call "relative affine structure". Via a number of corollaries of our main results we show that our framework unifies previous work --- including Euclidean, projective and affine --- in a natural and simple way, and introduces new, extremely simple, algorithms for the tasks of reconstruction from multiple views, recognition by alignment, and certain image coding applications
Discrete and continuum third quantization of Gravity
We give a brief introduction to matrix models and the group field theory
(GFT) formalism as realizations of the idea of a third quantization of gravity,
and present in some more detail the idea and basic features of a continuum
third quantization formalism in terms of a field theory on the space of
connections, building up on the results of loop quantum gravity that allow to
make the idea slightly more concrete. We explore to what extent one can
rigorously define such a field theory. Concrete examples are given for the
simple case of Riemannian GR in 3 spacetime dimensions. We discuss the relation
between GFT and this formal continuum third quantized gravity, and what it can
teach us about the continuum limit of GFTs.Comment: 21 pages, 5 eps figures; submitted as a contribution to the
proceedings of the conference "Quantum Field Theory and Gravity Conference
Regensburg 2010" (28 September - 1 October 2010, Regensburg/Bavaria); v2:
preprint number include
A new protocol for texture mapping process and 2d representation of rupestrian architecture
The development of the survey techniques for architecture and archaeology requires a general review in the methods used for the representation of numerical data. The possibilities offered by data processing allow to find new paths for studying issues connected to the drawing discipline. The research project aimed at experimenting different approaches for the representation of the rupestrian architecture and the texture mapping process. The nature of the rupestrian architecture does not allow a traditional representation of sections and projections of edges and outlines. The paper presents a method, the Equidistant Multiple Sections (EMS), inspired by cartography and based on the use of isohipses generated from different geometric plane. A specific paragraph is dedicated to the
texture mapping process for unstructured surface models. One of the main difficulty in the image projection consists in the recognition of homologous points between image and point cloud, above all in the areas with most deformations. With the aid of the “virtual scan” tool a different procedure was developed for improving the correspondences of the image. The result show a sensible improvement of the entire process above all for the architectural vaults. A detailed study concerned the unfolding of the straight line surfaces; the barrel vault of the analyzed chapel has been unfolded for observing the paintings in the real shapes out of the morphological context
Cayley-Dickson Algebras and Finite Geometry
Given a -dimensional Cayley-Dickson algebra, where , we
first observe that the multiplication table of its imaginary units , , is encoded in the properties of the projective space
PG if one regards these imaginary units as points and distinguished
triads of them , and , as lines. This projective space is seen to feature two distinct kinds
of lines according as or . Consequently, it also exhibits
(at least two) different types of points in dependence on how many lines of
either kind pass through each of them. In order to account for such partition
of the PG, the concept of Veldkamp space of a finite point-line
incidence structure is employed. The corresponding point-line incidence
structure is found to be a binomial -configuration ; in particular,
(octonions) is isomorphic to the Pasch -configuration,
(sedenions) is the famous Desargues -configuration,
(32-nions) coincides with the Cayley-Salmon -configuration found
in the well-known Pascal mystic hexagram and (64-nions) is
identical with a particular -configuration that can be viewed as
four triangles in perspective from a line where the points of perspectivity of
six pairs of them form a Pasch configuration. We also draw attention to a
remarkable nesting pattern formed by these configurations, where occurs as a geometric hyperplane of . Finally, a brief
examination of the structure of generic leads to a conjecture that
is isomorphic to a combinatorial Grassmannian of type .Comment: 26 pages, 20 figures; V2 - the basis made explicit, a footnote and a
couple of references adde
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