249 research outputs found
Can we make a Finsler metric complete by a trivial projective change?
A trivial projective change of a Finsler metric is the Finsler metric . I explain when it is possible to make a given Finsler metric both
forward and backward complete by a trivial projective change.
The problem actually came from lorentz geometry and mathematical relativity:
it was observed that it is possible to understand the light-line geodesics of a
(normalized, standard) stationary 4-dimensional space-time as geodesics of a
certain Finsler Randers metric on a 3-dimensional manifold. The trivial
projective change of the Finsler metric corresponds to the choice of another
3-dimensional slice, and the existence of a trivial projective change that is
forward and backward complete is equivalent to the global hyperbolicity of the
space-time.Comment: 11 pages, one figure, submitted to the proceedings of VI
International Meeting on Lorentzian Geometry (Granada
Finsler geodesics in the presence of a convex function and their applications
We obtain a result about the existence of only a finite number of geodesics
between two fixed non-conjugate points in a Finsler manifold endowed with a
convex function. We apply it to Randers and Zermelo metrics. As a by-product,
we also get a result about the finiteness of the number of lightlike and
timelike geodesics connecting an event to a line in a standard stationary
spacetime.Comment: 16 pages, AMSLaTex. v2 is a minor revision: title changed, references
updated, typos fixed; it matches the published version. This preprint and
arXiv:math/0702323v3 [math.DG] substitute arXiv:math/0702323v2 [math.DG
The causal structure of spacetime is a parameterized Randers geometry
There is a by now well-established isomorphism between stationary
4-dimensional spacetimes and 3-dimensional purely spatial Randers geometries -
these Randers geometries being a particular case of the more general class of
3-dimensional Finsler geometries. We point out that in stably causal
spacetimes, by using the (time-dependent) ADM decomposition, this result can be
extended to general non-stationary spacetimes - the causal structure (conformal
structure) of the full spacetime is completely encoded in a parameterized
(time-dependent) class of Randers spaces, which can then be used to define a
Fermat principle, and also to reconstruct the null cones and causal structure.Comment: 8 page
Infinitesimal and local convexity of a hypersurface in a semi-Riemannian manifold
Given a Riemannian manifold M and a hypersurface H in M, it is well known
that infinitesimal convexity on a neighborhood of a point in H implies local
convexity. We show in this note that the same result holds in a semi-Riemannian
manifold. We make some remarks for the case when only timelike, null or
spacelike geodesics are involved. The notion of geometric convexity is also
reviewed and some applications to geodesic connectedness of an open subset of a
Lorentzian manifold are given.Comment: 14 pages, AMSLaTex, 2 figures. v2: typos fixed, added one reference
and several comments, statement of last proposition correcte
The artificial retina for track reconstruction at the LHC crossing rate
We present the results of an R&D study for a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel and silicon strip detectors at , thus suitable for
processing LHC events at the full crossing frequency. For this purpose we
design and test a massively parallel pattern-recognition algorithm, inspired to
the current understanding of the mechanisms adopted by the primary visual
cortex of mammals in the early stages of visual-information processing. The
detailed geometry and charged-particle's activity of a large tracking detector
are simulated and used to assess the performance of the artificial retina
algorithm. We find that high-quality tracking in large detectors is possible
with sub-microsecond latencies when the algorithm is implemented in modern,
high-speed, high-bandwidth FPGA devices.Comment: 3 pages, 3 figures, ICHEP14. arXiv admin note: text overlap with
arXiv:1409.089
Simulation and performance of an artificial retina for 40 MHz track reconstruction
We present the results of a detailed simulation of the artificial retina
pattern-recognition algorithm, designed to reconstruct events with hundreds of
charged-particle tracks in pixel and silicon detectors at LHCb with LHC
crossing frequency of . Performances of the artificial retina
algorithm are assessed using the official Monte Carlo samples of the LHCb
experiment. We found performances for the retina pattern-recognition algorithm
comparable with the full LHCb reconstruction algorithm.Comment: Final draft of WIT proceedings modified according to JINST referee's
comment
On the energy functional on Finsler manifolds and applications to stationary spacetimes
In this paper we first study some global properties of the energy functional
on a non-reversible Finsler manifold. In particular we present a fully detailed
proof of the Palais--Smale condition under the completeness of the Finsler
metric. Moreover we define a Finsler metric of Randers type, which we call
Fermat metric, associated to a conformally standard stationary spacetime. We
shall study the influence of the Fermat metric on the causal properties of the
spacetime, mainly the global hyperbolicity. Moreover we study the relations
between the energy functional of the Fermat metric and the Fermat principle for
the light rays in the spacetime. This allows us to obtain existence and
multiplicity results for light rays, using the Finsler theory. Finally the case
of timelike geodesics with fixed energy is considered.Comment: 23 pages, AMSLaTeX. v4 matches the published versio
The artificial retina processor for track reconstruction at the LHC crossing rate
We present results of an R&D study for a specialized processor capable of
precisely reconstructing, in pixel detectors, hundreds of charged-particle
tracks from high-energy collisions at 40 MHz rate. We apply a highly parallel
pattern-recognition algorithm, inspired by studies of the processing of visual
images by the brain as it happens in nature, and describe in detail an
efficient hardware implementation in high-speed, high-bandwidth FPGA devices.
This is the first detailed demonstration of reconstruction of offline-quality
tracks at 40 MHz and makes the device suitable for processing Large Hadron
Collider events at the full crossing frequency.Comment: 4th draft of WIT proceedings modified according to JINST referee's
comments. 10 pages, 6 figures, 2 table
A Specialized Processor for Track Reconstruction at the LHC Crossing Rate
We present the results of an R&D study of a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel detectors at 40 MHz, thus suitable for processing LHC events at the full
crossing frequency. For this purpose we design and test a massively parallel
pattern-recognition algorithm, inspired by studies of the processing of visual
images by the brain as it happens in nature. We find that high-quality tracking
in large detectors is possible with sub-s latencies when this algorithm is
implemented in modern, high-speed, high-bandwidth FPGA devices. This opens a
possibility of making track reconstruction happen transparently as part of the
detector readout.Comment: Presented by G.Punzi at the conference on "Instrumentation for
Colliding Beam Physics" (INSTR14), 24 Feb to 1 Mar 2014, Novosibirsk, Russia.
Submitted to JINST proceeding
First prototype of a silicon tracker using an artificial retina for fast track finding
We report on the R\&D for a first prototype of a silicon tracker based on an
alternative approach for fast track finding. The working principle is inspired
from neurobiology, in particular by the processing of visual images by the
brain as it happens in nature. It is based on extensive parallelisation of data
distribution and pattern recognition. In this work we present the design of a
practical device that consists of a telescope based on single-sided silicon
detectors; we describe the data acquisition system and the implementation of
the track finding algorithms using available digital logic of commercial FPGA
devices. Tracking performance and trigger capabilities of the device are
discussed along with perspectives for future applications.Comment: 9 pages, 7 figures, Technology and Instrumentation in Particle
Physics 2014 (TIPP 2014), conference proceeding
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