190 research outputs found
From AdS Black Holes to Supersymmetric Flux-branes
We show that AdS black hole solutions admit an analytical continuation to
become magnetic flux-branes. Although a BPS AdS black hole generally has a
naked singularity, the BPS flux-brane can be regular everywhere with an
appropriate choice of U(1)-charges. This flux-brane interpolates from AdS_{D-2}
\times H^2 at small distance to an asymptotic AdS_D-type metric with an
AdS_{D-2}\times S^1 boundary. We also obtain a smooth cosmological solution of
de Sitter Einstein-Maxwell gravity which flows from dS_2\times S^{D-2} in the
infinite past to a dS_D-type metric, with an S^{D-2}\times S^1 boundary, in the
infinite future.Comment: Plain latex, 25 pages, references adde
Nuclear Parton Distribution Functions
We study nuclear effects of charged current deep inelastic neutrino-iron
scattering in the framework of a chi^2 analysis of parton distribution
functions (PDFs). We extract a set of iron PDFs which are used to compute
x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure
functions which are required in global analyses of free nucleon PDFs. We
compare our results with nuclear correction factors from neutrino-nucleus
scattering models and correction factors for charged-lepton--iron scattering.
We find that, except for very high x_Bj, our correction factors differ in both
shape and magnitude from the correction factors of the models and
charged-lepton scattering.Comment: 11 pages, 6 figures, to appear in the proceedings of the Ringberg
Workshop "New Trends in HERA Physics 2008
General Relativistic MHD Jets
Magnetic fields connecting the immediate environs of rotating black holes to
large distances appear to be the most promising mechanism for launching
relativistic jets, an idea first developed by Blandford and Znajek in the
mid-1970s. To enable an understanding of this process, we provide a brief
introduction to dynamics and electromagnetism in the spacetime near black
holes. We then present a brief summary of the classical Blandford-Znajek
mechanism and its conceptual foundations. Recently, it has become possible to
study these effects in much greater detail using numerical simulation. After
discussing which aspects of the problem can be handled well by numerical means
and which aspects remain beyond the grasp of such methods, we summarize their
results so far. Simulations have confirmed that processes akin to the classical
Blandford-Znajek mechanism can launch powerful electromagnetically-dominated
jets, and have shown how the jet luminosity can be related to black hole spin
and concurrent accretion rate. However, they have also shown that the
luminosity and variability of jets can depend strongly on magnetic field
geometry. We close with a discussion of several important open questions.Comment: 21 pages, 2 figures, To appear in Belloni, T. (ed.): The Jet Paradigm
- From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
Ultrarelativistic black hole in an external electromagnetic field and gravitational waves in the Melvin universe
We investigate the ultrarelativistic boost of a Schwarzschild black hole
immersed in an external electromagnetic field, described by an exact solution
of the Einstein-Maxwell equations found by Ernst (the ``Schwarzschild-Melvin''
metric). Following the classical method of Aichelburg and Sexl, the
gravitational field generated by a black hole moving ``with the speed of
light'' and the transformed electromagnetic field are determined. The
corresponding exact solution describes an impulsive gravitational wave
propagating in the static, cylindrically symmetric, electrovac universe of
Melvin, and for a vanishing electromagnetic field it reduces to the well known
Aichelburg-Sexl pp-wave. In the boosting process, the original Petrov type I of
the Schwarzschild-Melvin solution simplifies to the type II on the impulse, and
to the type D elsewhere. The geometry of the wave front is studied, in
particular its non-constant Gauss curvature. In addition, a more general class
of impulsive waves in the Melvin universe is constructed by means of a
six-dimensional embedding formalism adapted to the background. A coordinate
system is also presented in which all the impulsive metrics take a continuous
form. Finally, it is shown that these solutions are a limiting case of a family
of exact gravitational waves with an arbitrary profile. This family is
identified with a solution previously found by Garfinkle and Melvin. We thus
complement their analysis, in particular demonstrating that such spacetimes are
of type II and belong to the Kundt class.Comment: 11 pages, REVTeX
Role of electromagnetically induced transparency in resonant four-wave-mixing schemes.
Published versio
Near Horizon Analysis of Extremal AdS5 Black Holes
We study the near horizon geometry of extremal black holes in five
dimensional gauged supergravity using Sen's entropy function formalism. Special
attention is paid to the large black hole limit where the near horizon solution
exhibits a universal dependence on the rotation. The physical properties of the
large black hole solution are shown to agree with predictions from fluid
mechanical description of the dual conformal field theory.Comment: 26 pages, 1 figure; v2. clarifications and references adde
Gravitational Radiation Theory and Light Propagation
The paper gives an introduction to the gravitational radiation theory of isolated sources and to the propagation properties of light rays in radiative gravitational fields. It presents a theoretical study of the generation, propagation, back-reaction, and detection of gravitational waves from astrophysical sources. After reviewing the various quadrupole-moment laws for gravitational radiation in the Newtonian approximation, we show how to incorporate post-Newtonian corrections into the source multipole moments, the radiative multipole moments at infinity, and the back-reaction potentials. We further treat the light propagation in the linearized gravitational field outside a gravitational wave emitting source. The effects of time delay, bending of light, and moving source frequency shift are presented in terms of the gravitational lens potential. Time delay results are applied in the description of the procedure of the detection of gravitational waves
Gamma-induced background in the KATRIN main spectrometer
International audienceThe KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c 2 . It investigates the kinematics of β -particles from tritium β -decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about 12% of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than 17% (90% confidence level) of the overall MS background
The design, construction, and commissioning of the KATRIN experiment
The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns
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Energetic particle influence on the Earth's atmosphere
This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally
galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere
are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere
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