8,677 research outputs found
Charged Dilatonic AdS Black Branes in Arbitrary Dimensions
We study electromagnetically charged dilatonic black brane solutions in
arbitrary dimensions with flat transverse spaces, that are asymptotically AdS.
This class of solutions includes spacetimes which possess a bulk region where
the metric is approximately invariant under Lifshitz scalings. Given fixed
asymptotic boundary conditions, we analyze how the behavior of the bulk up to
the horizon varies with the charges and derive the extremality conditions for
these spacetimes.Comment: References update
Stable non-uniform black strings below the critical dimension
The higher-dimensional vacuum Einstein equation admits translationally
non-uniform black string solutions. It has been argued that infinitesimally
non-uniform black strings should be unstable in 13 or fewer dimensions and
otherwise stable. We construct numerically non-uniform black string solutions
in 11, 12, 13, 14 and 15 dimensions. Their stability is investigated using
local Penrose inequalities. Weakly non-uniform solutions behave as expected.
However, in 12 and 13 dimensions, strongly non-uniform solutions appear to be
stable and can have greater horizon area than a uniform string of the same
mass. In 14 and 15 dimensions all non-uniform black strings appear to be
stable.Comment: 26 pages, 11 figures. V2: reference added, matches published versio
Dynamical Cobordisms in General Relativity and String Theory
We describe a class of time-dependent solutions in string- or M-theory that
are exact with respect to alpha-prime and curvature corrections and interpolate
in physical space between regions in which the low energy physics is
well-approximated by different string theories and string compactifications.
The regions are connected by expanding "domain walls" but are not separated by
causal horizons, and physical excitations can propagate between them. As
specific examples we construct solutions that interpolate between oriented and
unoriented string theories, and also between type II and heterotic theories.
Our solutions can be weakly curved and under perturbative control everywhere
and can asymptote to supersymmetric at late times.Comment: 35 pages, 5 figures, LaTeX v2: reference adde
Heavy quark density in N=4 SYM: from hedgehog to Lifshitz spacetimes
We study the effect of an order N^2 density of heavy quarks in strongly
coupled N=4 SUSY Yang-Mills theory in the large N limit. This is achieved in
the type IIB supergravity dual by introducing a uniformly smeared density of
macroscopic string sources stretching to the boundary of AdS_5 x S^5. The
backreacted system exhibits a flow from an AdS_5 "hedgehog" geometry to a
scaling Lifshitz-like solution Lif_5 x S^5 with dynamical critical exponent
z=7, wherein the scaling symmetry is broken by a logarithmic running dilaton.
We find an exact black brane solution within the scaling regime which describes
the low temperature thermodynamics of the system.Comment: 20 pages, 2 figures, references adde
A scalar field instability of rotating and charged black holes in (4+1)-dimensional Anti-de Sitter space-time
We study the stability of static as well as of rotating and charged black
holes in (4+1)-dimensional Anti-de Sitter space-time which possess spherical
horizon topology. We observe a non-linear instability related to the
condensation of a charged, tachyonic scalar field and construct "hairy" black
hole solutions of the full system of coupled Einstein, Maxwell and scalar field
equations. We observe that the limiting solution for small horizon radius is
either a hairy soliton solution or a singular solution that is not a regular
extremal solution. Within the context of the gauge/gravity duality the
condensation of the scalar field describes a holographic
conductor/superconductor phase transition on the surface of a sphere.Comment: 16 pages including 8 figures, v2: discussion on soliton solutions
extended; v3: matches version accepted for publication in JHE
The FGK formalism for black p-branes in d dimensions
We present a generalization to an arbitrary number of spacetime (d) and
worldvolume (p+1) dimensions of the formalism proposed by Ferrara, Gibbons and
Kallosh to study black holes (p=0) in d=4 dimensions. We include the special
cases in which there can be dyonic and self- or anti-self-dual black branes.
Most of the results valid for 4-dimensional black holes (relations between
temperature, entropy and non-extremality parameter, and between entropy and
black-hole potential on the horizon) are straightforwardly generalized.
We apply the formalism to the case of black strings in N=2,d=5 supergravity
coupled to vector multiplets, in which the black-string potential can be
expressed in terms of the dual central charge and work out an explicit example
with one vector multiplet, determining supersymmetric and non-supersymmetric
attractors and constructing the non-extremal black-string solutions that
interpolate between them.Comment: 28 pages no figures; v2: some references adde
Generic master equations for quasi-normal frequencies
Generic master equations governing the highly-damped quasi-normal frequencies
[QNFs] of one-horizon, two-horizon, and even three-horizon spacetimes can be
obtained through either semi-analytic or monodromy techniques. While many
technical details differ, both between the semi-analytic and monodromy
approaches, and quite often among various authors seeking to apply the
monodromy technique, there is nevertheless widespread agreement regarding the
the general form of the QNF master equations. Within this class of generic
master equations we can establish some rather general results, relating the
existence of "families" of QNFs of the form omega_{a,n} = (offset)_a + i n
(gap) to the question of whether or not certain ratios of parameters are
rational or irrational.Comment: 23 pages; V2: Minor additions, typos fixed. Matches published versio
Optical Breath Gas Sensor for Extravehicular Activity Application
The function of the infrared gas transducer used during extravehicular activity (EVA) in the current space suit is to measure and report the concentration of carbon dioxide (CO2) in the ventilation loop. The next generation Portable Life Support System (PLSS) requires next generation CO2 sensing technology with performance beyond that presently in use on the Shuttle/International Space Station extravehicular mobility unit (EMU). Accommodation within space suits demands that optical sensors meet stringent size, weight, and power requirements. A laser diode (LD) spectrometer based on wavelength modulation spectroscopy (WMS) is being developed for this purpose by Vista Photonics, Inc. Two prototype devices were delivered to NASA Johnson Space Center (JSC) in September 2011. The sensors incorporate a laser diode based CO2 channel that also includes an incidental water vapor (humidity) measurement and a separate oxygen (O2) channel using a vertical cavity surface emitting laser (VCSEL). Both prototypes are controlled digitally with a field-programmable gate array (FPGA)/microcontroller architecture. Based on the results of the initial instrument development, further prototype development and testing of instruments leveraging the lessons learned were desired. The present development extends and upgrades the earlier hardware to the Advanced PLSS 2.0 test article being constructed and tested at JSC. Various improvements to the electronics and gas sampling are being advanced by this project. The combination of low power electronics with the performance of a long wavelength laser spectrometer enables multi-gas sensors with significantly increased performance over that presently offered in the EMU.
Phase transition and hyperscaling violation for scalar Black Branes
We investigate the thermodynamical behavior and the scaling symmetries of the
scalar dressed black brane (BB) solutions of a recently proposed, exactly
integrable Einstein-scalar gravity model [1], which also arises as
compactification of (p-1)-branes with a smeared charge. The extremal, zero
temperature, solution is a scalar soliton interpolating between a conformal
invariant AdS vacuum in the near-horizon region and a scale covariant metric
(generating hyperscaling violation on the boundary field theory)
asymptotically. We show explicitly that for the boundary field theory this
implies the emergence of an UV length scale (related to the size of the brane),
which decouples in the IR, where conformal invariance is restored. We also show
that at high temperatures the system undergoes a phase transition. Whereas at
small temperature the Schwarzschild-AdS BB is stable, above a critical
temperature the scale covariant, scalar-dressed BB solution, becomes
energetically preferred. We calculate the critical exponent z and the
hyperscaling violation parameter of the scalar-dressed phase. In particular we
show that the hyperscaling violation parameter is always negative. We also show
that the above features are not a peculiarity of the exact integrable model of
Ref.[1], but are a quite generic feature of Einstein-scalar and
Einstein-Maxwell-scalar gravity models for which the squared-mass of the scalar
field is positive and the potential vanishes exponentially as the scalar field
goes to minus infinity.Comment: 20 pages, 4 figures. In the revised version it has been pointed out
that the Einstein-scalar gravity model considered in the paper also arises as
compactification of black p-branes with smeared charge
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