47 research outputs found

### Is the equivalence principle useful for understanding general relativity?

The Equivalence Principle (EP) is at the heart of General Relativity (GR),
tested in many aspects. It is often used to discuss qualitatively the influence
of gravity on physical phenomena. But can this be made more precise? We compare
clock rates, frequency shifts, light deflection and time delay in simple static
spacetimes to the analogous phenomena seen by accelerated observers in
Minkowski space. In contrast to previous studies, we do not assume that the
gravitational field is weak and see, as we proceed, how the field is
constrained by the EP. Special care is taken that results are only observer-,
but not coordinate-dependent. By this we clarify some of the issues raised in
the literature and show which gravitational effects can and which cannot be
simulated by acceleration. The paper may also serve as a contribution for
critical discussions on the implications of the EP.Comment: 5 figure

### Symmetries of pp-Waves with Distributional Profile

We generalize the classification of (non-vacuum) pp-waves \cite{JEK} based on
the Killing-algebra of the space-time by admitting distribution-valued profile
functions. Our approach is based on the analysis of the (infinite-dimensional)
group of ``normal-form-preserving'' diffeomorphisms.Comment: 10 pages, latex2e, no figures, statement about the combination of
symmetry classes of impulsive waves correcte

### Canonical Formulation of pp-waves

We construct a Hamiltonian formulation for the class of plane-fronted
gravitational waves with parallel rays (pp-waves). Because of the existence of
a light-like Killing vector, the dynamics is effectively reduced to a 2+1
evolution with "time" chosen to be light-like. In spite of the vanishing action
this allows us to geometrically identify a symplectic form as well as dynamical
Hamiltonian, thus casting the system into canonical form.Comment: To appear in the "Obregon Festschrift

### ADM and Bondi four-momenta for the ultrarelativistic Schwarzschild black hole

We argue that it is possible to assign Bondi as well as ADM four-momentum to
the ultrarelativistic limit of the Schwarzschild black hole in agreement to
what is expected on physical grounds: The Bondi-momentum is lightlike and equal
to the ADM-momentum up to the retarded time when particle and radiation escape
to infinity and drops to zero thereafter, leaving flat space behind.Comment: Changes in the expression used for the ADM four-momentum without
altering the result, correction of some minor typing error

### A Note on the Symmetries of the Gravitational Field of a Massless Particle

It is shown that the metric of a massless particle obtained from boosting the
Schwarzschild metric to the velocity of light, has four Killing vectors
corresponding to an E(2)\times \RR symmetry-group. This is in agreement with
the expectations based on flat-space kinematics but is in contrast to previous
statements in the literature \cite{Schueck}. Moreover, it also goes beyond the
general Jordan-Ehlers-Kundt-(JEK)-classification of gravitational pp-waves as
given in \cite{JEK}.Comment: 10pages, amslatex, TUW-94-12 and UWThPh-1994-2

### Generalized Symmetries of Impulsive Gravitational Waves

We generalize previous \cite{AiBa2} work on the classification of
($C^\infty$) symmetries of plane-fronted waves with an impulsive profile. Due
to the specific form of the profile it is possible to extend the group of
normal-form-preserving diffeomorphisms to include non-smooth transformations.
This extension entails a richer structure of the symmetry algebra generated by
the (non-smooth) Killing vectors.Comment: 18 pages, latex2e, no figure

### Head-on collision of ultrarelativistic charges

We consider the head-on collision of two opposite-charged point particles
moving at the speed of light. Starting from the field of a single charge we
derive in a first step the field generated by uniformly accelerated charge in
the limit of infinite acceleration. From this we then calculate explicitly the
burst of radiation emitted from the head-on collision of two charges and
discuss its distributional structure. The motivation for our investigation
comes from the corresponding gravitational situation where the head-on
collision of two ultrarelativistic particles (black holes) has recently aroused
renewed interest.Comment: 4 figures, uses the AMSmat