146 research outputs found
String theory extensions of Einstein-Maxwell fields: the static case
We present a new approach for generation of solutions in the four-dimensional
heterotic string theory with one vector field and in the five-dimensional
bosonic string theory starting from the static Einstein-Maxwell fields. Our
approach allows one to construct the solution classes invariant with respect to
the total subgroup of the three-dimensional charging symmetries of these string
theories. The new generation procedure leads to the extremal
Israel-Wilson-Perjes subclass of string theory solutions in a special case and
provides its natural continuous extension to the realm of non-extremal
solutions. We explicitly calculate all string theory solutions related to
three-dimensional gravity coupled to an effective dilaton field which arises
after an appropriate charging symmetry invariant reduction of the static
Einstein-Maxwell system.Comment: 19 pages in late
Particle motion around magnetized black holes: Preston-Poisson space-time
We analyze motion of massless and massive particles around black holes
immersed in an asymptotically uniform magnetic field and surrounded by some
mechanical structure, which provides the magnetic field. The space-time is
described by Preston-Poisson metric, which is the generalization of the
well-known Ernst metric with a new parameter, tidal force, characterizing the
surrounding structure. The Hamilton-Jacobi equations allow separation of
variables in the equatorial plane. The presence of tidal force from
surroundings considerably changes parameters of the test particle motion: it
increases the radius of circular orbits of particles, increases the binding
energy of massive particles going from a given circular orbits to the innermost
stable orbit near black hole. In addition, it increases the distance of minimal
approach, time delay and bending angle for a ray of light propagating near
black hole.Comment: 6 pages, RevTex, the version accepted for publication in Phys. Rev.
Chiral models in dilaton-Maxwell gravity
We study symmetry properties of the Einstein-Maxwell theory nonminimaly
coupled to the dilaton field. We consider a static case with pure electric
(magnetic) Maxwell field and show that the resulting system becomes a nonlinear
sigma-model wich possesses a chiral representation. We construct the
corresponding chiral matrix and establish a representation which is related to
the pair of Ernst-like potentials. These potentials are used for separation of
the symmetry group into the gauge and nongauge (charging) sectors. New
variables, which linearize the action of charging symmetries, are also
established; a solution generation technique based on the use of charging
symmetries is formulated. This technique is used for generation of the
elecricaly (magneticaly) charged dilatonic fields from the static General
Relativity ones.Comment: 9 pages in LaTex; published in Gen. Rel. Grav. 32 (2000) pp 1389-139
Radiation reaction and energy-momentum conservation
We discuss subtle points of the momentum balance for radiating particles in
flat and curved space-time. An instantaneous balance is obscured by the
presence of the Schott term which is a finite part of the bound field momentum.
To establish the balance one has to take into account the initial and final
conditions for acceleration, or to apply averaging. In curved space-time an
additional contribution arises from the tidal deformation of the bound field.
This force is shown to be the finite remnant from the mass renormalization and
it is different both form the radiation recoil force and the Schott force. For
radiation of non-gravitational nature from point particles in curved space-time
the reaction force can be computed substituting the retarded field directly to
the equations of motion. Similar procedure is applicable to gravitational
radiation in vacuum space-time, but fails in the non-vacuum case. The existence
of the gravitational quasilocal reaction force in this general case seems
implausible, though it still exists in the non-relativistic approximation. We
also explain the putative antidamping effect for gravitational radiation under
non-geodesic motion and derive the non-relativistic gravitational quadrupole
Schott term. Radiation reaction in curved space of dimension other than four is
also discussedComment: Lecture given at the C.N.R.S. School "Mass and Motion in General
Relativity", Orleans, France, 200
3D heterotic string theory: new approach and extremal solutions
We develop a new formalism for the bosonic sector of low-energy heterotic
string theory toroidally compactified to three dimensions. This formalism is
based on the use of some single non-quadratic real matrix potential which
transforms linearly under the action of subgroup of the three-dimensional
charging symmetries. We formulate a new charging symmetry invariant approach
for the symmetry generation and straightforward construction of asymptotically
flat solutions. Finally, using the developed approach and the established
formal analogy between the heterotic and Einstein-Maxwell theories, we
construct a general class of the heterotic string theory extremal solutions of
the Israel-Wilson-Perjes type. This class is asymptotically flat and charging
symmetry complete; it includes the extremal solutions constructed before and
possesses the non-trivial bosonic string theory limit.Comment: 20 pages in Late
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