1,640 research outputs found
Subleading Soft Factor for String Disk Amplitudes
We investigate the behavior of superstring disk scattering amplitudes in the
presence of a soft external momentum at finite string tension. We prove that
there are no -corrections to the field theory form of the subleading
soft factor . At the end of this work, we also comment on the
possibility to find the corresponding subleading soft factors in closed string
theory using our result and the KLT relations.Comment: 15 pages, v2: minor changes, new references, version accepted by JHE
Bonus Yangian Symmetry for the Planar S-Matrix of N=4 Super Yang-Mills
Recent developments in the determination of the planar S-matrix of N=4 Super
Yang-Mills are closely related to its Yangian symmetry. Here we provide
evidence for a yet unobserved additional symmetry: the Yangian level-one
helicity operator.Comment: 8 pages, v2: minor change
Soft Black Hole Absorption Rates as Conservation Laws
The absorption rate of low-energy, or soft, electromagnetic radiation by
spherically symmetric black holes in arbitrary dimensions is shown to be fixed
by conservation of energy and large gauge transformations. We interpret this
result as the explicit realization of the Hawking-Perry-Strominger Ward
identity for large gauge transformations in the background of a non-evaporating
black hole. Along the way we rederive and extend previous analytic results
regarding the absorption rate for the minimal scalar and the photon.Comment: 20 Pages, 1 figur
New Phases of Water Ice Predicted at Megabar Pressures
Based on density functional calculations we predict water ice to attain two
new crystal structures with Pbca and Cmcm symmetry at 7.6 and 15.5 Mbar,
respectively. The known high pressure ice phases VII, VIII, X, and Pbcm as well
as the Pbca phase are all insulating and composed of two interpenetrating
hydrogen bonded networks, but the Cmcm structure is metallic and consists of
corrugated sheets of H and O atoms. The H atoms are squeezed into octahedral
positions between next-nearest O atoms while they occupy tetrahedral positions
between nearest O atoms in the ice X, Pbcm, and Pbca phases.Comment: submitted to Physical Review Letters on Jan 25, 201
Null Polygonal Wilson Loops in Full N=4 Superspace
We compute the one-loop expectation value of light-like polygonal Wilson
loops in N=4 super-Yang-Mills theory in full superspace. When projecting to
chiral superspace we recover the known results for tree-level
next-to-maximally-helicity-violating (NMHV) scattering amplitude. The one-loop
MHV amplitude is also included in our result but there are additional terms
which do not immediately correspond to scattering amplitudes. We finally
discuss different regularizations and their Yangian anomalies.Comment: 55 pages, v2: reference adde
D-region blunt probe data analysis using hybrid computer techniques
The feasibility of performing data reduction techniques with a hybrid computer was studied. The data was obtained from the flight of a parachute born probe through the D-region of the ionosphere. A presentation of the theory of blunt probe operation is included with emphasis on the equations necessary to perform the analysis. This is followed by a discussion of computer program development. Included in this discussion is a comparison of computer and hand reduction results for the blunt probe launched on 31 January 1972. The comparison showed that it was both feasible and desirable to use the computer for data reduction. The results of computer data reduction performed on flight data acquired from five blunt probes are also presented
Cauchy-perturbative matching revisited: tests in spherical symmetry
During the last few years progress has been made on several fronts making it
possible to revisit Cauchy-perturbative matching (CPM) in numerical relativity
in a more robust and accurate way. This paper is the first in a series where we
plan to analyze CPM in the light of these new results.
Here we start by testing high-order summation-by-parts operators, penalty
boundaries and contraint-preserving boundary conditions applied to CPM in a
setting that is simple enough to study all the ingredients in great detail:
Einstein's equations in spherical symmetry, describing a black hole coupled to
a massless scalar field. We show that with the techniques described above, the
errors introduced by Cauchy-perturbative matching are very small, and that very
long term and accurate CPM evolutions can be achieved. Our tests include the
accretion and ring-down phase of a Schwarzschild black hole with CPM, where we
find that the discrete evolution introduces, with a low spatial resolution of
\Delta r = M/10, an error of 0.3% after an evolution time of 1,000,000 M. For a
black hole of solar mass, this corresponds to approximately 5 s, and is
therefore at the lower end of timescales discussed e.g. in the collapsar model
of gamma-ray burst engines.
(abridged)Comment: 14 pages, 20 figure
Electrophoresis of colloidal dispersions in the low-salt regime
We study the electrophoretic mobility of spherical charged colloids in a
low-salt suspension as a function of the colloidal concentration. Using an
effective particle charge and a reduced screening parameter, we map the data
for systems with different particle charges and sizes, including numerical
simulation data with full electrostatics and hydrodynamics and experimental
data for latex dispersions, on a single master curve. We observe two different
volume fraction-dependent regimes for the electrophoretic mobility that can be
explained in terms of the static properties of the ionic double layer.Comment: Substantially revised versio
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