172 research outputs found
Singularities inside non-Abelian black holes
Singularities inside static spherically symmetric black holes in the SU(2)
Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theories are investigated.
Analytical formulas are presented describing oscillatory and power law metric
behavior near spacelike singularities in generic solutions.Comment: REVTeX, 9 pages, 2 EPS figures, uses epsf.st
Cylindrically symmetric solitons in Einstein-Yang-Mills theory
Recently new Einstein-Yang-Mills (EYM) soliton solutions were presented which
describe superconducting strings with Kasner asymptotic (hep-th/0610183). Here
we study the static cylindrically symmetric SU(2) EYM system in more detail.
The ansatz for the gauge field corresponds to superposition of the azimuthal
and the longitudinal components of the color magnetic field. We
derive sum rules relating data on the symmetry axis to asymptotic data and show
that generic asymptotic structure of regular solutions is Kasner. Solutions
starting with vacuum data on the axis generically are divergent. Regular
solutions correspond to some bifurcation manifold in the space of parameters
which has the low-energy limiting point corresponding to string solutions in
flat space (with the divergent total energy) and the high-curvature point where
gravity is crucial. Some analytical results are presented for the low energy
limit, and numerical bifurcation curves are constructed in the gravitating
case. Depending on the parameters, the solution looks like a straight string or
a pair of straight and circular strings. The existence of such non-linear
superposition of two strings becomes possible due to self-interaction terms in
the Yang-Mills action which suppress contribution of the circular string near
the polar axis.Comment: 21 pages, 11 figure
Weakly magnetized black holes as particle accelerators
We study collision of particles in the vicinity of a horizon of a weakly
magnetized non-rotating black hole. In the presence of the magnetic field
innermost stable circular orbits (ISCO) of charged particles can be located
close to the horizon. We demonstrate that for a collision of two particles, one
of which is charged and revolving at ISCO and the other is neutral and falling
from infinity, the maximal collision energy can be high in the limit of strong
magnetic field. This effect has some similarity with the recently discussed
effect of high center-of-mass energy for collision of particles in extremely
rotating black holes. We also demonstrate that for `realistic' astrophysical
black holes their ability to play the role of `accelerators' is in fact quite
restricted.Comment: 7 pages, 5 figure
Ehlers-Harrison transformations and black holes in Dilaton-Axion Gravity with multiple vector fields
Dilaton-axion gravity with vector fields is studied on space-times
admitting a timelike Killing vector field. Three-dimensional sigma-model is
derived in terms of K\"ahler geometry, and holomorphic representation of the
SO(2,2+p) global symmetry is constructed. A general static black hole solution
depending on parameters is obtained via SO(2,2+p) covariantization of
the Schwarzschild solution. The metric in the curvature coordinates looks as
the variable mass Reissner-Nordstr\"om one and generically possesses two
horizons. The inner horizon is pushed to the singularity if electric and
magnetic SO(p) charge vectors are parallel. For non-parallel charges the inner
horizon has a finite area except for an extremal limit when this property is
preserved only for orthogonal charges. Extremal dyon configurations with
orthogonal charges have finite horizon radii continuously varying from zero to
the ADM mass. New general solution is endowed with a NUT parameter, asymptotic
values of dilaton and axion, and a gauge parameter which can be used to ascribe
any given value to one of scalar charges.Comment: 37 pages, Late
Sp(4,R)/GL(2,R) Matrix Structure of Geodesic Solutions for Einstein--Maxwell--Dilaton--Axion Theory
The constructed matrix operator defines the family of
isotropic geodesic containing vacuum point lines in the target space of the
stationary D=4 Einstein--Maxwell--dilaton--axion theory. This operator is used
to derive a class of solutions which describes a point center system with
nontrivial values of mass, parameter NUT, as well as electric, magnetic,
dilaton and axion charges. It is shown that this class contains both particular
solutions Majumdar--Papapetrou--like black holes and massless asymptotically
nonflat naked singularities.Comment: 20 pages, RevTex, no figures, Submitted to Phys.Rev.
Chromo-Natural Inflation: Natural inflation on a steep potential with classical non-Abelian gauge fields
We propose a model for inflation consisting of an axionic scalar field
coupled to a set of three non-Abelian gauge fields. Our model's novel
requirement is that the gauge fields begin inflation with a rotationally
invariant vacuum expectation value (VEV) that is preserved through
identification of SU(2) gauge invariance with rotations in three dimensions.
The gauge VEV interacts with the background value of the axion, leading to an
attractor solution that exhibits slow roll inflation even when the axion decay
constant has a natural value (). Assuming a sinusoidal potential
for the axion, we find that inflation continues until the axionic potential
vanishes. The speed at which the axion moves along its potential is modulated
by its interactions with the gauge VEV, rather than being determined by the
slope of its bare potential. For sub-Plankian axion decay constants vanishingly
small tensor to scalar ratios are predicted, a direct consequence of the Lyth
bound. The parameter that controls the interaction strength between the axion
and the gauge fields requires a technically natural tuning of
(100).Comment: v2: 5 pages, no figures. Version accepted to PR
BPS Solutions in D=5 Dilaton-Axion Gravity
We show that the D=5 dilaton-axion gravity compactified on a 2-torus
possesses the SL(4,R)/SO(4) matrix formulation. It is used for construction of
the SO(2,2)-invariant BPS solution depended on the one harmonic function.Comment: presented at GR1
Bertotti-Robinson type solutions to Dilaton-Axion Gravity
We present a new solution to dilaton-axion gravity which looks like a
rotating Bertotti-Robinson (BR) Universe. It is supported by an homogeneous
Maxwell field and a linear axion and can be obtained as a near-horizon limit of
extremal rotating dilaton-axion black holes. It has the isometry where U(1) is the remnant of the SO(3) symmetry of BR broken by rotation,
while corresponds to the sector which no longer factors out
of the full spacetime. Alternatively our solution can be obtained from the D=5
vacuum counterpart to the dyonic BR with equal electric and magnetic field
strengths. The derivation amounts to smearing it in D=6 and then reducing to
D=4 with dualization of one Kaluza-Klein two-form in D=5 to produce an axion.
Using a similar dualization procedure, the rotating BR solution is uplifted to
D=11 supergravity. We show that it breaks all supersymmetries of N=4
supergravity in D=4, and that its higher dimensional embeddings are not
supersymmetric either. But, hopefully it may provide a new arena for corformal
mechanics and holography. Applying a complex coordinate transformation we also
derive a BR solution endowed with a NUT parameter.Comment: 21 page
Late time tails of the massive vector field in a black hole background
We investigate the late-time behavior of the massive vector field in the
background of the Schwarzschild and Schwarzschild-de Sitter black holes. For
Schwarzschild black hole, at intermediately late times the massive vector field
is represented by three functions with different decay law , ,
, while at asymptotically late times
the decay law is universal, and does not
depend on the multipole number . Together with previous study of massive
scalar and Dirac fields where the same asymptotically late-time decay law was
found, it means, that the asymptotically late-time decay law \emph{does not depend} also \emph{on the spin} of the field under
consideration. For Schwarzschild-de Sitter black holes it is observed two
different regimes in the late-time decay of perturbations: non-oscillatory
exponential damping for small values of and oscillatory quasinormal mode
decay for high enough . Numerical and analytical results are found for these
quasinormal frequencies.Comment: one author and new material are adde
Vacuum polarization near cosmic string in RS2 brane world
Gravitational field of cosmic strings in theories with extra spatial
dimensions must differ significantly from that in the Einstein's theory. This
means that all gravity induced properties of cosmic strings need to be revised
too. Here we consider the effect of vacuum polarization outside a straight
infinitely thin cosmic string embedded in a RS2 brane world. Perturbation
technique combined with the method of dimensional regularization is used to
calculate for a massless scalar field.Comment: 8 pages, RevTeX
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