14,832 research outputs found
Magnetic monopoles and vortices in the standard model of electroweak interactions
These lectures start with an elementary introduction to the subject of
magnetic monopoles which should be accesible from any physics background. In
the Weinberg-Salam model of electroweak interactions, magnetic monopoles appear
at the ends of a type of non-topological vortices called electroweak strings.
These will also be discussed, as well as recent simulations of their formation
during a phase transition which indicate that, in the (unphysical) range of
parameters in which the strings are classically stable, they can form with a
density comparable to topological vortices.Comment: 19 pages, Les Houches lectures, NATO-ASI on Topological defects and
the non-equilibrium dynamics of symmetry breaking phase transitions, Feb. 9
Solitons as Key Parts to Produce a Universe in the Laboratory
Cosmology is usually understood as an observational science, where
experimentation plays no role. It is interesting, nevertheless, to change this
perspective addressing the following question: what should we do to create a
universe, in a laboratory? It appears, in fact, that this is, in principle,
possible according to at least two different paradigms; both allow to
circumvent singularity theorems, i.e. the necessity of singularities in the
past of inflating domains which have the required properties to generate a
universe similar to ours. The first of them is substantially classical, and is
built up considering solitons which collide with surrounding topological
defects, generating an inflationary domain of space-time. The second is,
instead, partly quantum and considers the possibility of tunnelling of
past-non-singular regions of spacetime into an inflating universe, following a
well-known instanton proposal.
We are, here, going to review some of these models, as well as highlight
possible extensions, generalizations and the open issues (as for instance the
detectability of child universes and the properties of quantum tunnelling
processes) that still affect the description of their dynamics. In doing so we
will remark how the works on this subject can represent virtual laboratories to
test the role that fundamental principles of physics (particularly, the
interplay of quantum and general relativistic realms) played in the formation
of our universe.Comment: Based on a talk given at the 2006 Biennial Meeting of the
International Association for Relativistic Dynamics (IARD06). 11 pages, LaTe
Causal Fermion Systems as a Candidate for a Unified Physical Theory
The theory of causal fermion systems is an approach to describe fundamental
physics. Giving quantum mechanics, general relativity and quantum field theory
as limiting cases, it is a candidate for a unified physical theory. We here
give a non-technical introduction.Comment: 19 pages, LaTeX, minor improvements (published version
Modeling self-organization in pedestrians and animal groups from macroscopic and microscopic viewpoints
This paper is concerned with mathematical modeling of intelligent systems,
such as human crowds and animal groups. In particular, the focus is on the
emergence of different self-organized patterns from non-locality and anisotropy
of the interactions among individuals. A mathematical technique by
time-evolving measures is introduced to deal with both macroscopic and
microscopic scales within a unified modeling framework. Then self-organization
issues are investigated and numerically reproduced at the proper scale,
according to the kind of agents under consideration.Comment: 24 pages, 13 figure
Jet Methods in Time-Dependent Lagrangian Biomechanics
In this paper we propose the time-dependent generalization of an `ordinary'
autonomous human biomechanics, in which total mechanical + biochemical energy
is not conserved. We introduce a general framework for time-dependent
biomechanics in terms of jet manifolds associated to the extended
musculo-skeletal configuration manifold, called the configuration bundle. We
start with an ordinary configuration manifold of human body motion, given as a
set of its all active degrees of freedom (DOF) for a particular movement. This
is a Riemannian manifold with a material metric tensor given by the total
mass-inertia matrix of the human body segments. This is the base manifold for
standard autonomous biomechanics. To make its time-dependent generalization, we
need to extend it with a real time axis. By this extension, using techniques
from fibre bundles, we defined the biomechanical configuration bundle. On the
biomechanical bundle we define vector-fields, differential forms and affine
connections, as well as the associated jet manifolds. Using the formalism of
jet manifolds of velocities and accelerations, we develop the time-dependent
Lagrangian biomechanics. Its underlying geometric evolution is given by the
Ricci flow equation.
Keywords: Human time-dependent biomechanics, configuration bundle, jet
spaces, Ricci flowComment: 13 pages, 3 figure
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