Papers by Athanasios Economou
Multiple-soliton solutions of Einstein’s equations
Journal of Mathematical Physics, 1989
ABSTRACT Using the Belinsky–Zakharov generating technique and a flat metric as a seed, two‐ and f... more ABSTRACT Using the Belinsky–Zakharov generating technique and a flat metric as a seed, two‐ and four‐soliton solutions of the Einstein vacuum equations for the cases of stationary axisymmetric, cylindrically symmetric, or plane symmetric gravitational fields are considered. Three‐ and five‐parameter classes of exact solutions are obtained, some of which are new.
Quantum Processes near Cosmic-Strings
The Origin of Structure in the Universe, 1993
Gravitational effects of traveling waves along global cosmic strings
Physical Review D, 1992
Making use of the relationship between the corresponding field configurations, we derive the metr... more Making use of the relationship between the corresponding field configurations, we derive the metric around a straight global cosmic string with traveling waves in terms of the static metric (without traveling waves) in the weak-field limit. We discuss under which conditions the effect of the traveling waves may overcome the repulsive gravitational potential of the static straight global string. We
Physical Review D, 1994
We point out that in general the Reissner-Nordstr\"om (RN) charged black holes of general relativ... more We point out that in general the Reissner-Nordstr\"om (RN) charged black holes of general relativity are not solutions of the four dimensional quadratic gravitational theories. They are, e.g., exact solutions of the $R+R^2$ quadratic theory but not of a theory where a $R_{ab}R^{ab}$ term is present in the gravitational Lagrangian. In the case where such a non linear curvature term is present with sufficiently small coupling, we obtain an approximate solution for a charged black hole of charge $Q$ and mass $M$. For $Q\ll M$ the validity of this solution extends down to the horizon. This allows us to explore the thermodynamic properties of the quadratic charged black hole and we find that, to our approximation, its thermodynamics is identical to that of a RN black hole. However our black hole's entropy is not equal to the one fourth of the horizon area. Finally we extend our analysis to the rotating charged black hole and qualitatively similar results are obtained.
Conical bremsstrahlung in a cosmic-string spacetime
Physical Review D, 1991
Quantum-field-theoretical processes near cosmic strings: Transition probabilities and localization
Physical Review D, 1991
... In partic-ular, the gravitational field for an infinite, straight, and static (ISS) gauge cos... more ... In partic-ular, the gravitational field for an infinite, straight, and static (ISS) gauge cosmic string, idealized to be infinitely thin, is represented by a flat, cylindrically symmetric spacetime with a conical axis of ... In this spacetime there exists glo-bally a timelike Killing vector field. ...
The gravitational field of monopoles, cosmic strings and domain walls is studied in the quadratic... more The gravitational field of monopoles, cosmic strings and domain walls is studied in the quadratic gravitational theory R + αR 2 with α|R| ≪ 1, and is compared with the result in Einstein's theory. The metric aquires modifications which correspond to a short range 'Newtonian' potential for gauge cosmic strings, gauge monopoles and domain walls and to a long range one for global monopoles and global cosmic strings. In this theory the corrections turn out to be attractive for all the defects. We explain, however, that the sign of these corrections in general depends on the particular higher order derivative theory and topological defect under consideration. The possible relevance of our results to the study of the evolution of topological defects in the early universe is pointed out.
General Relativity and Gravitation, 1988
The gravitational field along the symmetry axis of the Kerr spacetime is examined. The equations ... more The gravitational field along the symmetry axis of the Kerr spacetime is examined. The equations of parallel transport along this axis are solved for the timelike geodesics case, and the corresponding tidal tensor is constructed.
Physics Letters A, 1986
A gyroscope following a closed polar orbit in the Kerr spacetime is considered. An exact expressi... more A gyroscope following a closed polar orbit in the Kerr spacetime is considered. An exact expression is derived giving the shift of the gyroscope's orientation per revolution in terms of the mass and angular momentum parameters of the Kerr metric and the orbit's coordinate radius.
Physical Review Letters, 1988
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Papers by Athanasios Economou