16,070 research outputs found
Bosonic string - Kaluza Klein theory exact solutions using 5D-6D dualities
We present the explicit formulae which allow to transform the general
solution of the 6D Kaluza--Klein theory on a 3--torus into the special solution
of the 6D bosonic string theory on a 3--torus as well as into the general
solution of the 5D bosonic string theory on a 2--torus. We construct a new
family of the extremal solutions of the 3D chiral equation for the
SL(4,R)/SO(4) coset matrix and interpret it in terms of the component fields of
these three duality related theories.Comment: 13 pages in LaTe
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
Expansionfree Fluid Evolution and Skripkin Model in f(R) Theory
We consider the modified theory of gravity whose higher order
curvature terms are interpreted as a gravitational fluid or dark source. The
gravitational collapse of a spherically symmetric star, made up of locally
anisotropic viscous fluid, is studied under the general influence of the
curvature fluid. Dynamical equations and junction conditions are modified in
the context of f(R) dark energy and by taking into account the expansionfree
evolution of the self-gravitating fluid. As a particular example, the Skripkin
model is investigated which corresponds to isotropic pressure with constant
energy density. The results are compared with corresponding results in General
Relativity.Comment: 18 pages, accepted for publication Int. J. Mod. Phys.
String theory extensions of Einstein-Maxwell fields: the stationary case
We present a new approach for generating solutions in heterotic string theory
compactified down to three dimensions on a torus with d+n>2, where d and n
stand for the number of compactified space--time dimensions and Abelian gauge
fields, respectively. It is shown that in the case when d=2k+1 and n is
arbitrary, one can apply a solution--generating procedure starting from
solutions of the stationary Einstein theory with k Maxwell fields; our approach
leads to classes of solutions which are invariant with respect to the total
group of three-dimensional charging symmetries. We consider a particular
extension of the stationary Einstein--multi-Maxwell theory obtained on the
basis of the Kerr--multi-Newman--NUT special class of solutions and establish
the conditions under which the resulting multi--dimensional metric is free of
Dirac string peculiarities.Comment: 19 pages in late
Charging Interacting Rotating Black Holes in Heterotic String Theory
We present a formulation of the stationary bosonic string sector of the whole
toroidally compactified effective field theory of the heterotic string as a
double Ernst system which, in the framework of General Relativity describes, in
particular, a pair of interacting spinning black holes; however, in the
framework of low--energy string theory the double Ernst system can be
particularly interpreted as the rotating field configuration of two interacting
sources of black hole type coupled to dilaton and Kalb--Ramond fields. We
clarify the rotating character of the --component of the
antisymmetric tensor field of Kalb--Ramond and discuss on its possible torsion
nature. We also recall the fact that the double Ernst system possesses a
discrete symmetry which is used to relate physically different string vacua.
Therefore we apply the normalized Harrison transformation (a charging symmetry
which acts on the target space of the low--energy heterotic string theory
preserving the asymptotics of the transformed fields and endowing them with
multiple electromagnetic charges) on a generic solution of the double Ernst
system and compute the generated field configurations for the 4D effective
field theory of the heterotic string. This transformation generates the
vector field content of the whole low--energy heterotic string
spectrum and gives rise to a pair of interacting rotating black holes endowed
with dilaton, Kalb--Ramond and multiple electromagnetic fields where the charge
vectors are orthogonal to each other.Comment: 15 pages in latex, revised versio
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