12,491 research outputs found
Inflating magnetically charged braneworlds
Numerical solutions of Einstein, scalar, and gauge field equations are found
for static and inflating defects in a higher-dimensional spacetime. The defects
have -dimensional core and magnetic monopole configuration in
extra dimensions. For symmetry-breaking scale below the critical value
, the defects are characterized by a flat worldsheet geometry and
asymptotically flat extra dimensions. The critical scale is comparable
to the higher-dimensional Planck scale and has some dependence on the gauge and
scalar couplings. For , the extra dimensions degenerate into a
`cigar', and for all static solutions are singular. The
singularity can be removed if the requirement of staticity is relaxed and
defect cores are allowed to inflate. The inflating solutions have de Sitter
worldsheets and cigar geometry in the extra dimensions. Exact analytic
solutions describing the asymptotic behavior of these inflating monopoles are
found and the parameter space of these solutions is analyzed.Comment: 35 pages, revtex, 18 eps figure
Vortex simulations of the RayleighâTaylor instability
A vortex technique capable of calculating the RayleighâTaylor instability to large amplitudes in inviscid, incompressible, layered flows is introduced. The results show the formation of a steadyâstate bubble at large times, whose velocity is in agreement with the theory of Birkhoff and Carter. It is shown that the spike acceleration can exceed free fall, as suggested recently by Menikoff and Zemach. Results are also presented for instability at various Atwood ratios and for fluids having several layers
Inertial range turbulence in kinetic plasmas
The transfer of turbulent energy through an inertial range from the driving
scale to dissipative scales in a kinetic plasma followed by the conversion of
this energy into heat is a fundamental plasma physics process. A theoretical
foundation for the study of this process is constructed, but the details of the
kinetic cascade are not well understood. Several important properties are
identified: (a) the conservation of a generalized energy by the cascade; (b)
the need for collisions to increase entropy and realize irreversible plasma
heating; and (c) the key role played by the entropy cascade--a dual cascade of
energy to small scales in both physical and velocity space--to convert
ultimately the turbulent energy into heat. A strategy for nonlinear numerical
simulations of kinetic turbulence is outlined. Initial numerical results are
consistent with the operation of the entropy cascade. Inertial range turbulence
arises in a broad range of space and astrophysical plasmas and may play an
important role in the thermalization of fusion energy in burning plasmas.Comment: 11 pages, 2 figures, submitted to Physics of Plasmas, DPP Meeting
Special Issu
The hunt for the Milky Way's accreted disc
The Milky Way is expected to host an accreted disc of stars and dark matter.
This forms as massive >1:10 mergers are preferentially dragged towards the disc
plane by dynamical friction and then tidally shredded. The accreted disc likely
contributes only a tiny fraction of the Milky Way's thin and thick stellar
disc. However, it is interesting because: (i) its associated `dark disc' has
important implications for experiments hoping to detect a dark matter particle
in the laboratory; and (ii) the presence or absence of such a disc constrains
the merger history of our Galaxy. In this work, we develop a chemo-dynamical
template to hunt for the accreted disc. We apply our template to the
high-resolution spectroscopic sample from Ruchti et al. (2011), finding at
present no evidence for accreted stars. Our results are consistent with a
quiescent Milky Way with no >1:10 mergers since the disc formed and a
correspondingly light `dark disc'. However, we caution that while our method
can robustly identify accreted stars, our incomplete stellar sample makes it
more challenging to definitively rule them out. Larger unbiased stellar samples
will be required for this.Comment: 14 pages; 8 figures; 1 table. Accepted for publication in MNRA
Schwarzschild solution in brane induced gravity
The metric of a Schwarzschild solution in brane induced gravity in five
dimensions is studied. We find a nonperturbative solution for which an exact
expression on the brane is obtained. We also find a linearized solution in the
bulk and argue that a nonsingular exact solution in the entire space should
exist. The exact solution on the brane is highly nontrivial as it interpolates
between different distance scales. This part of the metric is enough to deduce
an important property -- the ADM mass of the solution is suppressed compared to
the bare mass of a static source. This screening of the mass is due to
nonlinear interactions which give rise to a nonzero curvature outside the
source. The curvature extends away from the source to a certain macroscopic
distance that coincides with the would-be strong interaction scale. The very
same curvature shields the source from strong coupling effects. The four
dimensional law of gravity, including the correct tensorial structure, is
recovered at observable distances. We find that the solution has no vDVZ
discontinuity and show that the gravitational field on the brane is always
weak, in spite of the fact that the solution is nonperturbative.Comment: 23 pages, 2 figures, repetitions removed, PRD versio
Gravitational field of vacuumless defects
It has been recently shown that topological defects can arise in symmetry
breaking models where the scalar field potential has no minima and is
a monotonically decreasing function of . Here we study the
gravitational fields produced by such vacuumless defects in the cases of both
global and gauge symmetry breaking. We find that a global monopole has a
strongly repulsive gravitational field, and its spacetime has an event horizon
similar to that in de Sitter space. A gauge monopole spacetime is essentially
that of a magnetically charged black hole. The gravitational field of a global
string is repulsive and that of a gauge string is attractive at small distances
and repulsive at large distances. Both gauge and global string spacetimes have
singularities at a finite distance from the string core.Comment: 19 pages, REVTeX, 6 Postscript figure
Schwarzschild-De Sitter black holes in 4+1 dimensional bulk
We construct a static solution for 4+1 dimensional bulk such that the 3+1
dimensional world has a linear warp factor and describes the
Schwarzschild-dS_{4} black hole. For m=0 this four dimensional universe and
Friedmann Robertson Walker universe are related with an explicit coordinate
transformation. We emphasize that for linear warp factors the effect of bulk on
the brane world shows up as the dS_{4} background which is favored by the big
bang cosmology.Comment: 6 page
Strong gravitational lensing by braneworld black holes
In this paper, we use the strong field limit approach to investigate the
gravitational lensing properties of braneworld black holes. Applying this
method to the supermassive black hole at the centre of our galaxy, the lensing
observables for some candidate braneworld black hole metrics are compared with
those for the standard Schwarzschild case. It is found that braneworld black
holes could have significantly different observational signatures to the
Schwarzschild black hole.Comment: 8 pages, 4 figures, RevTeX4; v2 reference added; v3 minor technical
correctio
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