42 research outputs found
General relativity as an extended canonical gauge theory
It is widely accepted that the fundamental geometrical law of nature should
follow from an action principle. The particular subset of transformations of a
system's dynamical variables that maintain the form of the action principle
comprises the group of canonical transformations. In the context of canonical
field theory, the adjective "extended" signifies that not only the fields but
also the space-time geometry is subject to transformation. Thus, in order to be
physical, the transition to another, possibly noninertial frame of reference
must necessarily constitute an extended canonical transformation that defines
the general mapping of the connection coefficients, hence the quantities that
determine the space-time curvature and torsion of the respective reference
frame. The canonical transformation formalism defines simultaneously the
transformation rules for the conjugates of the connection coefficients and for
the Hamiltonian. As will be shown, this yields unambiguously a particular
Hamiltonian that is form-invariant under the canonical transformation of the
connection coefficients and thus satisfies the general principle of relativity.
This Hamiltonian turns out to be a quadratic function of the curvature tensor.
Its Legendre-transformed counterpart then establishes a unique Lagrangian
description of the dynamics of space-time that is not postulated but derived
from basic principles, namely the action principle and the general principle of
relativity. Moreover, the resulting theory satisfies the principle of scale
invariance and is renormalizable.Comment: 14 page
Hamiltonian dynamics on the symplectic extended phase space for autonomous and non-autonomous systems
We will present a consistent description of Hamiltonian dynamics on the
``symplectic extended phase space'' that is analogous to that of a
time-\underline{in}dependent Hamiltonian system on the conventional symplectic
phase space. The extended Hamiltonian and the pertaining extended
symplectic structure that establish the proper canonical extension of a
conventional Hamiltonian will be derived from a generalized formulation of
Hamilton's variational principle. The extended canonical transformation theory
then naturally permits transformations that also map the time scales of
original and destination system, while preserving the extended Hamiltonian
, and hence the form of the canonical equations derived from .
The Lorentz transformation, as well as time scaling transformations in
celestial mechanics, will be shown to represent particular canonical
transformations in the symplectic extended phase space. Furthermore, the
generalized canonical transformation approach allows to directly map explicitly
time-dependent Hamiltonians into time-independent ones. An ``extended''
generating function that defines transformations of this kind will be presented
for the time-dependent damped harmonic oscillator and for a general class of
explicitly time-dependent potentials. In the appendix, we will reestablish the
proper form of the extended Hamiltonian by means of a Legendre
transformation of the extended Lagrangian .Comment: 24 page
Stochastic effects in real and simulated charged particle beams
The Vlasov equation embodies the smooth field approximation of the
self-consistent equation of motion for charged particle beams. This framework
is fundamentally altered if we include the fluctuating forces that originate
from the actual charge granularity. We thereby perform the transition from a
reversible description to a statistical mechanics' description covering also
the irreversible aspects of beam dynamics. Taking into account contributions
from fluctuating forces is mandatory if we want to describe effects like
intrabeam scattering or temperature balancing within beams. Furthermore, the
appearance of ``discreteness errors'' in computer simulations of beams can be
modeled as ``exact'' beam dynamics that is being modified by fluctuating
``error forces''. It will be shown that the related emittance increase depends
on two distinct quantities: the magnitude of the fluctuating forces embodied in
a friction coefficient , and the correlation time dependent average
temperature anisotropy. These analytical results are verified by various
computer simulations.Comment: 11 pages, 9 figure
Generalized U(N) gauge transformations in the realm of the extended covariant Hamilton formalism of field theory
The Lagrangians and Hamiltonians of classical field theory require to
comprise gauge fields in order to be form-invariant under local gauge
transformations. These gauge fields have turned out to correctly describe
pertaining elementary particle interactions. In this paper, this principle is
extended to require additionly the form-invariance of a classical field theory
Hamiltonian under variations of the space-time curvature emerging from the
gauge fields. This approach is devised on the basis of the extended canonical
transformation formalism of classical field theory which allows for
transformations of the space-time metric in addition to transformations of the
fields. Working out the Hamiltonian that is form-invariant under extended local
gauge transformations, we can dismiss the conventional requirement for gauge
bosons to be massless in order for them to preserve the local gauge
invariance.The emerging equation of motion for the curvature scalar turns out
to be compatible with the Einstein equation in the case of a static gauge
field. The emerging equation of motion for the curvature scalar R turns out to
be compatible with that from a Proca system in the case of a static gauge
field.Comment: 27 page
Generic Theory of Geometrodynamics from Noether's theorem for the Diff(M) symmetry group
We work out the most general theory for the interaction of spacetime geometry
and matter fields---commonly referred to as geometrodynamics---for spin- and
spin- particles. The minimum set of postulates to be introduced is that (i)
the action principle should apply and that(ii) the total action should by
form-invariant under the (local) diffeomorphism group. The second postulate
thus implements the Principle of General Relativity. According to Noether's
theorem, this physical symmetry gives rise to a conserved Noether current, from
which the complete set of theories compatible with both postulates can be
deduced. This finally results in a new generic Einstein-type equation, which
can be interpreted as an energy-momentum balance equation emerging from the
Lagrangian for the source-free dynamics of gravitation and the
energy-momentum tensor of the source system . Provided that the system
has no other symmetries---such as SU---the canonical energy-momentum
tensor turns out to be the correct source term of gravitation. For the case of
massive spin particles, this entails an increased weighting of the kinetic
energy over the mass in their roles as the source of gravity as compared to the
metric energy momentum tensor, which constitutes the source of gravity in
Einstein's General Relativity. We furthermore confirm that a massive vector
field necessarily acts as a source for torsion of spacetime. Thus, from the
viewpoint of our generic Einstein-type equation, Einstein's General Relativity
constitutes the particular case for spin- and massless spin particle fields,
and the Hilbert Lagrangian as the model for the source-free dynamics
of gravitation.Comment: 33 page
Improved envelope and emittance description of particle beams using the Fokker-Planck approach
Beam dynamics calculations that are based on the Vlasov equation do not
permit the the treatment of stochastic phenomena such as intra-beam scattering.
If the nature of the stochastic process can be regarded as a Markov process, we
are allowed to use the Fokker-Planck equation to describe the change of the
phase space volume the beam occupies. From the Fokker-Planck equation we derive
equations of motion for the beam envelopes and for the rms-emittances. Compared
to previous approaches based on Liouville's theorem, these equations contain
additional terms that describe the temperature balancing within the beam. Our
formalism is applied to the effect of intra-beam scattering relevant for beams
circulating in storage rings near thermodynamical equilibrium. In this case,
the Fokker-Planck coefficients can be treated as adiabatic constants of motion.
Due to the simplified analysis based on `beam moments', we obtain fairly simple
equations that allow us to estimate the growth rate of the beam emittance.Comment: 24 pages, 3 figure
The problem of self-consistent particle phase space distributions for periodic focusing channels
Charged particle beams that remain stationary while passing through a
transport channel are represented by ``self-consistent'' phase space
distributions. As the starting point, we assume the external focusing forces to
act continuously on the beam. If Liouville's theorem applies, an infinite
variety of self-consistent particle phase space distributions exists then. The
method is reviewed how to determine the Hamiltonian of the focusing system for
a given phase space density function. Subsequently, this Hamiltonian is
transformed canonically to yield the appropriate Hamiltonian that pertains to a
beam passing through a non-continuous transport system. It is shown that the
total transverse beam energy is a conserved quantity, if the beam stays
rotationally symmetric along the channel. It can be concluded that charged
particle beams can be transmitted through periodic solenoid channels without
loss of quality. Our computer simulations, presented in the second part of the
paper, confirm this result. In contrast, the simulation for a periodic
quadrupole channel yields a small but constant growth rate of the
rms-emittance.Comment: 31 pages, 12 figure
Energy-second-moment map analysis as an approach to quantify the irregularity of Hamiltonian systems
A different approach will be presented that aims to scrutinize the
phase-space trajectories of a general class of Hamiltonian systems with regard
to their regular or irregular behavior. The approach is based on the
`energy-second-moment map' that can be constructed for all Hamiltonian systems
of the generic form . With a three-component vector
consisting of the system's energy and second moments , , this
map linearly relates the vector at time with the vector's initial
state at . It will turn out that this map is directly obtained from
the solution of a linear third-order equation that establishes an extension of
the set of canonical equations. The Lyapunov functions of the
energy-second-moment map will be shown to have simple analytical
representations in terms of the solutions of this linear third-order equation.
Applying Lyapunov's regularity analysis for linear systems, we will show that
the Lyapunov functions of the energy-second-moment map yields information on
the irregularity of the particular phase-space trajectory. Our results will be
illustrated by means of numerical examples.Comment: 9 pages, 7 figure