237 research outputs found
Bounding the ground-state energy of a many-body system with the differential method
This paper promotes the differential method as a new fruitful strategy for
estimating a ground-state energy of a many-body system. The case of an
arbitrary number of attractive Coulombian particles is specifically studied and
we make some favorable comparison of the differential method to the existing
approaches that rely on variational principles. A bird's-eye view of the
treatment of more general interactions is also given.Comment: version 1->2 (main revisions): subsection 2.2, equation (18),
footnote 6 have been adde
Third post-Newtonian constrained canonical dynamics for binary point masses in harmonic coordinates
The conservative dynamics of two point masses given in harmonic coordinates
up to the third post-Newtonian (3pN) order is treated within the framework of
constrained canonical dynamics. A representation of the approximate Poincar\'e
algebra is constructed with the aid of Dirac brackets. Uniqueness of the
generators of the Poincar\'e group resp. the integrals of motion is achieved by
imposing their action on the point mass coordinates to be identical with that
of the usual infinitesimal Poincar\'e transformations. The second
post-Coulombian approximation to the dynamics of two point charges as predicted
by Feynman-Wheeler electrodynamics in Lorentz gauge is treated similarly.Comment: 42 pages, submitted to Phys. Rev.
Asymptotic conditions of motion for radiating charged particles
Approximate asymptotic conditions on the motion of compact, electrically
charged particles are derived within the framework of general relativity using
the Einstein- Infeld-Hoffmann (EIH) surface integral method. While
superficially similar to the Abraham-Lorentz and Lorentz-Dirac (ALD) equations
of motion, these conditions differ from them in several fundamental ways. They
are not equations of motion in the usual sense but rather a set of conditions
which these motions must obey in the asymptotic future of an initial value
surface. In addition to being asymptotic, these conditions of motion are
approximate and apply, as do the original EIH equations, only to slowly moving
systems. Also, they do not admit the run- away solutions of these other
equations. As in the original EIH work, they are integrability conditions
gotten from integrating the empty-space (i.e., source free) Einstein-Maxwell
equations of general relativity over closed two-surfaces surrounding the
sources of the fields governed by these equations. No additional ad hoc
assumptions, such as the form of a force law or the introduction of inertial
reaction terms, needed to derive the ALD equations are required for this
purpose. Nor is there a need for any of the infinite mass renormalizations that
are required in deriving these other equations.Comment: 15 page
Kinetic theory of spatially inhomogeneous stellar systems without collective effects
We review and complete the kinetic theory of spatially inhomogeneous stellar
systems when collective effects (dressing of the stars by their polarization
cloud) are neglected. We start from the BBGKY hierarchy issued from the
Liouville equation and consider an expansion in powers of 1/N in a proper
thermodynamic limit. For , we obtain the Vlasov equation
describing the evolution of collisionless stellar systems like elliptical
galaxies. At the order 1/N, we obtain a kinetic equation describing the
evolution of collisional stellar systems like globular clusters. This equation
does not suffer logarithmic divergences at large scales since spatial
inhomogeneity is explicitly taken into account. Making a local approximation,
and introducing an upper cut-off at the Jeans length, it reduces to the
Vlasov-Landau equation which is the standard kinetic equation of stellar
systems. Our approach provides a simple and pedagogical derivation of these
important equations from the BBGKY hierarchy which is more rigorous for systems
with long-range interactions than the two-body encounters theory. Making an
adiabatic approximation, we write the generalized Landau equation in
angle-action variables and obtain a Landau-type kinetic equation that is valid
for fully inhomogeneous stellar systems and is free of divergences at large
scales. This equation is less general than the Lenard Balescu-type kinetic
equation recently derived by Heyvaerts (2010) since it neglects collective
effects, but it is substantially simpler and could be useful as a first step.
We discuss the evolution of the system as a whole and the relaxation of a test
star in a bath of field stars. We derive the corresponding Fokker-Planck
equation in angle-action variables and provide expressions for the diffusion
coefficient and friction force
Reduction of the two-body dynamics to a one-body description in classical electrodynamics
We discuss the mapping of the conservative part of two-body electrodynamics
onto that of a test charged particle moving in some external electromagnetic
field, taking into account recoil effects and relativistic corrections up to
second post-Coulombian order. Unlike the results recently obtained in general
relativity, we find that in classical electrodynamics it is not possible to
implement the matching without introducing external parameters in the effective
electromagnetic field. Relaxing the assumption that the effective test particle
moves in a flat spacetime provides a feasible way out.Comment: 20 pages, revtex; minor change
- âŠ