8,174 research outputs found
First-order action and Euclidean quantum gravity
We show that the on-shell path integral for asymptotically flat Euclidean
spacetimes can be given in the first-order formulation of general relativity,
without assuming the boundary to be isometrically embedded in Euclidean space
and without adding infinite counter-terms. For illustrative examples of our
approach, we evaluate the first-order action for the four-dimensional Euclidean
Schwarzschild and NUT-charged spacetimes to derive the corresponding on-shell
partition functions, and show that the correct thermodynamic quantities for the
solutions are reproduced.Comment: 8 pages; v2: references added; minor corrections; v3: typos corrected
in eqns (20) and (21); v4: substantially revised; addition of NUT-charged
spacetimes; to appear in Classical and Quantum Gravit
Torelli theorem for the parabolic Deligne-Hitchin moduli space
We prove that, given the isomorphism class of the parabolic Deligne-Hitchin
moduli space over a smooth projective curve, we can recover the isomorphism
class of the curve and the parabolic points.Comment: 20 page
Automorphism group of the moduli space of parabolic bundles over a curve
We find the automorphism group of the moduli space of parabolic bundles on a
smooth curve (with fixed determinant and system of weights). This group is
generated by: automorphisms of the marked curve, tensoring with a line bundle,
taking the dual, and Hecke transforms (using the filtrations given by the
parabolic structure). A Torelli theorem for parabolic bundles with arbitrary
rank and generic weights is also obtained. These results are extended to the
classification of birational equivalences which are defined over "big" open
subsets (3-birational maps, i.e. birational maps giving an isomorphism between
open subsets with complement of codimension at least 3).
Finally, an analysis of the stability chambers for the parabolic weights is
performed in order to determine precisely when two moduli spaces of parabolic
vector bundles with different parameters (curve, rank, determinant and weights)
can be isomorphic.Comment: 99 page
Charged rotating black holes in higher dimensions
We use a recent implementation of the large expansion in order to
construct the higher-dimensional Kerr-Newman black hole and also new charged
rotating black bar solutions of the Einstein-Maxwell theory, all with rotation
along a single plane. We describe the space of solutions, obtain their
quasinormal modes, and study the appearance of instabilities as the horizons
spread along the plane of rotation. Generically, the presence of charge makes
the solutions less stable. Instabilities can appear even when the angular
momentum of the black hole is small, as long as the charge is sufficiently
large. We expect that, although our study is performed in the limit
, the results provide a good approximation for charged rotating
black holes at finite .Comment: 21 pages, 1 figur
Augmented reality usage for prototyping speed up
The first part of the article describes our approach for solution of this
problem by means of Augmented Reality. The merging of the real world model and
digital objects allows streamline the work with the model and speed up the
whole production phase significantly. The main advantage of augmented reality
is the possibility of direct manipulation with the scene using a portable
digital camera. Also adding digital objects into the scene could be done using
identification markers placed on the surface of the model. Therefore it is not
necessary to work with special input devices and lose the contact with the real
world model. Adjustments are done directly on the model. The key problem of
outlined solution is the ability of identification of an object within the
camera picture and its replacement with the digital object. The second part of
the article is focused especially on the identification of exact position and
orientation of the marker within the picture. The identification marker is
generalized into the triple of points which represents a general plane in
space. There is discussed the space identification of these points and the
description of representation of their position and orientation be means of
transformation matrix. This matrix is used for rendering of the graphical
objects (e. g. in OpenGL and Direct3D).Comment: Keywords: augmented reality, prototyping, pose estimation,
transformation matri
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