12,974 research outputs found
Stability of Horava-Lifshitz Black Holes in the Context of AdS/CFT
The anti--de Sitter/conformal field theory (AdS/CFT) correspondence is a
powerful tool that promises to provide new insights toward a full understanding
of field theories under extreme conditions, including but not limited to
quark-gluon plasma, Fermi liquid and superconductor. In many such applications,
one typically models the field theory with asymptotically AdS black holes.
These black holes are subjected to stringy effects that might render them
unstable. Ho\v{r}ava-Lifshitz gravity, in which space and time undergo
different transformations, has attracted attentions due to its power-counting
renormalizability. In terms of AdS/CFT correspondence, Ho\v{r}ava-Lifshitz
black holes might be useful to model holographic superconductors with Lifshitz
scaling symmetry. It is thus interesting to study the stringy stability of
Ho\v{r}ava-Lifshitz black holes in the context of AdS/CFT. We find that
uncharged topological black holes in Ho\v{r}ava-Lifshitz theory are
nonperturbatively stable, unlike their counterparts in Einstein gravity, with
the possible exceptions of negatively curved black holes with detailed balance
parameter close to unity. Sufficiently charged flat black holes for
close to unity, and sufficiently charged positively curved black
holes with close to zero, are also unstable. The implication to the
Ho\v{r}ava-Lifshitz holographic superconductor is discussed.Comment: 15 pages, 6 figures. Updated version accepted by Phys. Rev. D, with
corrections to various misprints. References update
Optical transitions in highly-charged californium ions with high sensitivity to variation of the fine-structure constant
We study electronic transitions in highly-charged Cf ions that are within the
frequency range of optical lasers and have very high sensitivity to potential
variations in the fine-structure constant, alpha. The transitions are in the
optical despite the large ionisation energies because they lie on the
level-crossing of the 5f and 6p valence orbitals in the thallium isoelectronic
sequence. Cf16+ is a particularly rich ion, having several narrow lines with
properties that minimize certain systematic effects. Cf16+ has very large
nuclear charge and large ionisation energy, resulting in the largest
alpha-sensitivity seen in atomic systems. The lines include positive and
negative shifters
A wireless multi-sensor subglacial probe: design and preliminary results
This paper introduces a new way to investigate in situ processes, the wireless multi-sensor probe, as part of an environmental sensor network. Instruments are housed within a 'probe' which can move freely and so behave like a clast. These were deployed in the ice and till at Briksdalsbreen, Norway. The sensors measure temperature, resistivity, case stress, tilt angle and water pressure and send their data to a base station on the glacier surface via radio links. These data are then forwarded by radio to a reference station with mains power 2.5 km away, from where they are sent to a web server in the UK. The system deployed during 2004/05 was very successful and a total of 859 probe days worth of data from the ice and till were collected, along with GPS, weather and diagnostic data about the system
Characterization of a two-transmon processor with individual single-shot qubit readout
We report the characterization of a two-qubit processor implemented with two
capacitively coupled tunable superconducting qubits of the transmon type, each
qubit having its own non-destructive single-shot readout. The fixed capacitive
coupling yields the \sqrt{iSWAP} two-qubit gate for a suitable interaction
time. We reconstruct by state tomography the coherent dynamics of the two-bit
register as a function of the interaction time, observe a violation of the Bell
inequality by 22 standard deviations after correcting readout errors, and
measure by quantum process tomography a gate fidelity of 90%
Quantum Heating of a nonlinear resonator probed by a superconducting qubit
We measure the quantum fluctuations of a pumped nonlinear resonator, using a
superconducting artificial atom as an in-situ probe. The qubit excitation
spectrum gives access to the frequency and temperature of the intracavity field
fluctuations. These are found to be in agreement with theoretical predictions;
in particular we experimentally observe the phenomenon of quantum heating
TeV gamma-rays from photo-disintegration/de-excitation of cosmic-ray nuclei
It is commonly assumed that high-energy gamma-rays are made via either purely
electromagnetic processes or the hadronic process of pion production, followed
by decay. We investigate astrophysical contexts where a third process (A*) may
dominate, namely the photo-disintegration of highly boosted nuclei followed by
daughter de-excitation. Starbust regions such as Cygnus OB2 appear to be
promising sites for TeV gamma-ray emission via this mechanism. A unique feature
of the A* process is a sharp energy minimum ~ 10 TeV/(T/eV) for gamma-ray
emission from a thermal region of temperature T. We also check that a diffuse
gamma-ray component resulting from the interaction of a possible extreme-energy
cosmic-ray nuclei with background radiation is well below the observed EGRET
data. The A* mechanism described herein offers an important contribution to
gamma-ray astronomy in the era of intense observational activity.Comment: To be published in Phys. Rev. Let
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