208 research outputs found
Transverse Wave Propagation in Relativistic Two-fluid Plasmas in de Sitter Space
We investigate transverse electromagnetic waves propagating in a plasma in
the de Sitter space. Using the 3+1 formalism we derive the relativistic
two-fluid equations to take account of the effects due to the horizon and
describe the set of simultaneous linear equations for the perturbations. We use
a local approximation to investigate the one-dimensional radial propagation of
Alfv\'en and high frequency electromagnetic waves and solve the dispersion
relation for these waves numerically.Comment: 19 pages, 12 figure
Killing spectroscopy of closed timelike curves
We analyse the existence of closed timelike curves in spacetimes which
possess an isometry. In particular we check which discrete quotients of such
spaces lead to closed timelike curves. As a by-product of our analysis, we
prove that the notion of existence or non-existence of closed timelike curves
is a T-duality invariant notion, whenever the direction along which we apply
such transformations is everywhere spacelike. Our formalism is
straightforwardly applied to supersymmetric theories. We provide some new
examples in the context of D-branes and generalized pp-waves.Comment: 1+35 pages, no figures; v2, new references added. Final version to
appear in JHE
X-Ray Scattering Measurements of the Transient Structure of a Driven Charge-Density-Wave
We report time-resolved x-ray scattering measurements of the transient
structural response of the sliding {\bf Q} charge-density-wave (CDW) in
NbSe to a reversal of the driving electric field. The observed time scale
characterizing this response at 70K varies from 15 msec for driving
fields near threshold to 2 msec for fields well above threshold. The
position and time-dependent strain of the CDW is analyzed in terms of a
phenomenological equation of motion for the phase of the CDW order parameter.
The value of the damping constant, eV
seconds \AA, is in excellent agreement with the value
determined from transport measurements. As the driving field approaches
threshold from above, the line shape becomes bimodal, suggesting that the CDW
does not depin throughout the entire sample at one well-defined voltage.Comment: revtex 3.0, 7 figure
Spatial variations in lead isotopes, Tasman Element, eastern Australia
Lead isotope data from ore deposits and mineral occurrences in the Tasman Element of eastern Australia have been used to construct isotopic maps of this region. These maps exhibit systematic patterns in parameters derived from isotope ratios. The parameters include μ (238U/204Pb), as calculated using the Cumming and Richards (1975) lead evolution model, and the difference between true age of mineralisation and the Cumming and Richards lead isotope model age of mineralisation (Δt).
Variations in μ coincide with boundaries at the orogen, subprovince and zone scales. The boundary between the Lachlan and New England orogens is accompanied by a decrease in μ, and within the Lachlan Orogen, the Central Subprovince is characterised by μ that is significantly higher than in the adjacent Eastern and Western subprovinces. Within the Eastern Subprovince, the Cu-Au-rich Macquarie Arc is characterised by significantly lower μ relative to adjacent rocks.
The Macquarie Arc is also characterised by very high Δt (generally above 200 Myr). Other regions characterised by very high Δt include western Tasmania, the southeastern New England Orogen, and the Hodgkinson Province in northern Queensland. These anomalies are within a broad pattern of decreasing Δt from east to west, with Paleozoic deposits within or adjacent to Proterozoic crust characterised by Δt values of 50 Myr or below.
The patterns in Δt are interpreted to reflect the presence of the two major tectonic components involved in the Paleozoic Tasman margin in Australia (cf., Münker, 2000): subducting proto-Pacific crust (Δt >150 Myr), and Proterozoic Australia crust (Δt < 50 Myr) on the over-riding plate. Proterozoic Australia crustal sources are interpreted to dominate the western parts of the Tasman Element and Proterozoic crust further to the west, whereas Pacific crustal sources are inferred to characterise western Tasmania and much of the eastern part of the Tasman Element. Contrasts in Δt between the Cambrian Mount Read Volcanics in western Tasmania and similar aged rocks in western Victoria and New South Wales make direct tectonic correlation between these rocks problematic
Role of electromagnetically induced transparency in resonant four-wave-mixing schemes.
Published versio
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Holographic Hydrodynamics with a Chemical Potential
We consider five-dimensional gravity coupled to a negative cosmological
constant and a single U(1) gauge field, including a general set of
four-derivative interactions. In this framework, we construct charged planar
AdS black hole solutions perturbatively and consider the thermal and
hydrodynamic properties of the plasma in the dual CFT. In particular, we
calculate the ratio of shear viscosity to entropy density and argue that the
violation of the KSS bound is enhanced in the presence of a chemical potential.
We also compute the electrical conductivity and comment on various conjectured
bounds related to this coefficient.Comment: v2: comparison to supergravity lagrangian added, references added,
typos fixe
On the Perturbative Stability of the QCD Predictions for the Ratio in Heavy-Quark Leptoproduction
We analyze the perturbative and parametric stability of the QCD predictions
for the Callan-Gross ratio in heavy-quark leptoproduction.
We consider the radiative corrections to the dominant photon-gluon fusion
mechanism. In various kinematic regions, the following contributions are
investigated: exact NLO results at low and moderate ,
asymptotic NLO predictions at high , and both NLO and NNLO
soft-gluon (or threshold) corrections at large Bjorken . Our analysis shows
that large radiative corrections to the structure functions and
cancel each other in their ratio with good accuracy. As
a result, the NLO contributions to the Callan-Gross ratio are less than 10% in
a wide region of the variables and . We provide compact LO predictions
for in the case of low . A simple formula connecting the
high-energy behavior of the Callan-Gross ratio and low- asymptotics of the
gluon density is derived. It is shown that the obtained hadron-level
predictions for are stable under the DGLAP evolution of the
gluon distribution function. Our analytic results simplify the extraction of
the structure functions and from measurements of
the corresponding reduced cross sections, in particular at DESY HERA.Comment: 14 pages, 6 figures, revtex4; minor correction
On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection
A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)
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