2,010 research outputs found
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
Non-abelian magnetic black strings versus black holes
We present dimensional pure magnetic Yang-Mills (YM) black strings (or
branes) induced by the dimensional Einstein-Yang-Mills-Dilaton black
holes. Born-Infeld version of the YM field makes our starting point which goes
to the standard YM field through a limiting procedure. The lifting from black
holes to black strings, (with less number of fields) is by adding an extra,
compact coordinate. This amounts to the change of horizon topology from
to a product structure. Our black string in dimensions is a
rather special one, with uniform Hawking temperature and non-asymptotically
flat structure. As the YM charge becomes large the string gets thinner to tend
into a breaking point and transform into a % dimensional black hole.Comment: 5 pages no figure; Final version to appear in EPJ
Dimensional reduction in numerical relativity: Modified cartoon formalism and regularization
We present in detail the Einstein equations in the BaumgarteâShapiroâShibataâNakamura formulation for the case of D-dimensional spacetimes with SO(Dâd)isometry based on a method originally introduced in Ref. 1. Regularized expressions are given for a numerical implementation of this method on a vertex centered grid including the origin of the quasi-radial coordinate that covers the extra dimensions with rotational symmetry. Axisymmetry, corresponding to the value d = D â 2, represents a special case with fewer constraints on the vanishing of tensor components and is conveniently implemented in a variation of the general method. The robustness of the scheme is demonstrated for the case of a black-hole head-on collision in D = 7 spacetime dimensions with SO(4) symmetry.U.S. is supported by the H2020 ERC Consolidator Grant âMatter and strong-field gravity: New frontiers in Einsteinâs theoryâ grant agreement No. MaGRaThâ646597, the H2020-MSCA-RISE-2015 Grant No. StronGrHEP-690904, the STFC Consolidator Grant No. ST/L000636/1, the SDSC Comet and TACC Stampede clusters through NSF-XSEDE Award Nos. PHY-090003, the Cambridge High Performance Computing Service Supercomputer Darwin using Strategic Research Infrastructure Funding from the HEFCE and the STFC, and DiRACâs Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1. P.F. and S.T. are supported by the H2020 ERC Starting Grant âNew frontiers in numerical general relativityâ grant agreement No. NewNGR- 639022. P.F. is also supported by a Royal Society University Research Fellowship. W.G.C. and M.K. are supported by STFC studentships.This is the final version of the article. It first appeared from the World Scientific Publishing Company via http://dx.doi.org/10.1142/S021827181641013
Compositional random data: a routine for CoDaPack
Generation of random variables are needed in the simulations of many natural process. For
some random variables, di erent methodologies are known, specially into euclidean spaces. In this
paper a routine for dealing with random variables into a simplex space with the Aitchison geometry
is presented. The routine has been implemented for the CoDaPack, a freeware software developed
to be used for users with minimum programming skills
The shifted-scaled Dirichlet distribution in the simplex
Perturbation and powering are two operations in the simplex that define a vector-space structure.
Perturbation and powering in the simplex play the same role as the sum and product by
scalars in real space. A standard Dirichlet random composition can be shifted by perturbation, and
scaled powering by a real scalar. The obtained random composition has a shifted-scaled Dirichlet
distribution. The procedure is analogous to standardization of real random variables. The derived
distribution is a generalization of the Dirichlet one, and it is studied from a probabilistic point
of view. In the simplex, considered as an Euclidean space, the Aitchison measure is the natural
(Lebesgue type) measure, which is compatible with its operations and metrics. Therefore, a natural
way of describing the generalized (shifted-scaled) Dirichlet probability distributions is using probability
densities with respect to the Aitchison measure. This density representation is compared
with the traditional probability density with respect to the Lebesgue measure. In particular, the
center and variability for both representations are compared
Characterisation of AMS H35 HV-CMOS monolithic active pixel sensor prototypes for HEP applications
Monolithic active pixel sensors produced in High Voltage CMOS (HV-CMOS)
technology are being considered for High Energy Physics applications due to the
ease of production and the reduced costs. Such technology is especially
appealing when large areas to be covered and material budget are concerned.
This is the case of the outermost pixel layers of the future ATLAS tracking
detector for the HL-LHC. For experiments at hadron colliders, radiation
hardness is a key requirement which is not fulfilled by standard CMOS sensor
designs that collect charge by diffusion. This issue has been addressed by
depleted active pixel sensors in which electronics are embedded into a large
deep implantation ensuring uniform charge collection by drift. Very first small
prototypes of hybrid depleted active pixel sensors have already shown a
radiation hardness compatible with the ATLAS requirements. Nevertheless, to
compete with the present hybrid solutions a further reduction in costs
achievable by a fully monolithic design is desirable. The H35DEMO is a large
electrode full reticle demonstrator chip produced in AMS 350 nm HV-CMOS
technology by the collaboration of Karlsruher Institut f\"ur Technologie (KIT),
Institut de F\'isica d'Altes Energies (IFAE), University of Liverpool and
University of Geneva. It includes two large monolithic pixel matrices which can
be operated standalone. One of these two matrices has been characterised at
beam test before and after irradiation with protons and neutrons. Results
demonstrated the feasibility of producing radiation hard large area fully
monolithic pixel sensors in HV-CMOS technology. H35DEMO chips with a substrate
resistivity of 200 cm irradiated with neutrons showed a radiation
hardness up to a fluence of ncm with a hit efficiency of
about 99% and a noise occupancy lower than hits in a LHC bunch
crossing of 25ns at 150V
The Gaia spectrophotometric standard stars survey -II. Instrumental effects of six ground-based observing campaigns
The Gaia SpectroPhotometric Standard Stars (SPSS) survey started in 2006, it
was awarded almost 450 observing nights, and accumulated almost 100,000 raw
data frames, with both photometric and spectroscopic observations. Such large
observational effort requires careful, homogeneous, and automated data
reduction and quality control procedures. In this paper, we quantitatively
evaluate instrumental effects that might have a significant (i.e.,1%)
impact on the Gaia SPSS flux calibration. The measurements involve six
different instruments, monitored over the eight years of observations dedicated
to the Gaia flux standards campaigns: DOLORES@TNG in La Palma, EFOSC2@NTT and
ROSS@REM in La Silla, [email protected] in Calar Alto, BFOSC@Cassini in Loiano, and
[email protected] in San Pedro Martir. We examine and quantitatively evaluate the
following effects: CCD linearity and shutter times, calibration frames
stability, lamp flexures, second order contamination, light polarization, and
fringing. We present methods to correct for the relevant effects, which can be
applied to a wide range of observational projects at similar instruments.Comment: 16 pages, 13 figures, accepted for publication in Astron. Nach
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