5,905 research outputs found
Molecular dynamics simulations of complex shaped particles using Minkowski operators
The Minkowski operators (addition and substraction of sets in vectorial
spaces) has been extensively used for Computer Graphics and Image Processing to
represent complex shapes. Here we propose to apply those mathematical concepts
to extend the Molecular Dynamics (MD) Methods for simulations with
complex-shaped particles. A new concept of Voronoi-Minkowski diagrams is
introduced to generate random packings of complex-shaped particles with tunable
particle roundness. By extending the classical concept of Verlet list we
achieve numerical efficiencies that do not grow quadratically with the body
number of sides. Simulations of dissipative granular materials under shear
demonstrate that the method complies with the first law of thermodynamics for
energy balance.Comment: Submitted to Phys. Rev.
The shape dynamics description of gravity
Classical gravity can be described as a relational dynamical system without
ever appealing to spacetime or its geometry. This description is the so-called
shape dynamics description of gravity. The existence of relational first
principles from which the shape dynamics description of gravity can be derived
is a motivation to consider shape dynamics (rather than GR) as the fundamental
description of gravity. Adopting this point of view leads to the question: What
is the role of spacetime in the shape dynamics description of gravity? This
question contains many aspects: Compatibility of shape dynamics with the
description of gravity in terms of spacetime geometry, the role of local
Minkowski space, universality of spacetime geometry and the nature of quantum
particles, which can no longer be assumed to be irreducible representations of
the Poincare group. In this contribution I derive effective spacetime
structures by considering how matter fluctuations evolve along with shape
dynamics. This evolution reveals an "experienced spacetime geometry." This
leads (in an idealized approximation) to local Minkowski space and causal
relations. The small scale structure of the emergent geometric picture depends
on the specific probes used to experience spacetime, which limits the
applicability of effective spacetime to describe shape dynamics. I conclude
with discussing the nature of quantum fluctuations (particles) in shape
dynamics and how local Minkowski spacetime emerges from the evolution of
quantum particles.Comment: 16 pages Latex, no figures, arXiv version of a submission to the
proceedings of Theory Canada
An anthology of non-local QFT and QFT on noncommutative spacetime
Ever since the appearance of renormalization theory there have been several
differently motivated attempts at non-localized (in the sense of not generated
by point-like fields) relativistic particle theories, the most recent one being
at QFT on non-commutative Minkowski spacetime. The often conceptually
uncritical and historically forgetful contemporary approach to these problems
calls for a critical review the light of previous results on this subject.Comment: 33 pages tci-latex, improvements of formulations, shortening of
sentences, addition of some reference
Quantum Theory as Universal Theory of Structures – Essentially from Cosmos to Consciousness
Quantum theory is the most successful physical theory ever. About one third of the gross national product in the developed countries results from its applications. These applications range from nuclear power to most of the high-tech tools for computing, laser, solar cells and so on. No limit for its range of validity has been found up to now..
Observer dependent entanglement
Understanding the observer-dependent nature of quantum entanglement has been
a central question in relativistic quantum information. In this paper we will
review key results on relativistic entanglement in flat and curved spacetime
and discuss recent work which shows that motion and gravity have observable
effects on entanglement between localized systems.Comment: Ivette Fuentes previously published as Ivette Fuentes-Guridi and
Ivette Fuentes-Schulle
About Lorentz invariance in a discrete quantum setting
A common misconception is that Lorentz invariance is inconsistent with a
discrete spacetime structure and a minimal length: under Lorentz contraction, a
Planck length ruler would be seen as smaller by a boosted observer. We argue
that in the context of quantum gravity, the distance between two points becomes
an operator and show through a toy model, inspired by Loop Quantum Gravity,
that the notion of a quantum of geometry and of discrete spectra of geometric
operators, is not inconsistent with Lorentz invariance. The main feature of the
model is that a state of definite length for a given observer turns into a
superposition of eigenstates of the length operator when seen by a boosted
observer. More generally, we discuss the issue of actually measuring distances
taking into account the limitations imposed by quantum gravity considerations
and we analyze the notion of distance and the phenomenon of Lorentz contraction
in the framework of ``deformed (or doubly) special relativity'' (DSR), which
tentatively provides an effective description of quantum gravity around a flat
background. In order to do this we study the Hilbert space structure of DSR,
and study various quantum geometric operators acting on it and analyze their
spectral properties. We also discuss the notion of spacetime point in DSR in
terms of coherent states. We show how the way Lorentz invariance is preserved
in this context is analogous to that in the toy model.Comment: 25 pages, RevTe
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