3,843 research outputs found
Holographic predictions for cosmological 3-point functions
We present the holographic predictions for cosmological 3-point correlators,
involving both scalar and tensor modes, for a universe which started in a
non-geometric holographic phase. Holographic formulae relate the cosmological
3-point functions to stress tensor correlation functions of a holographically
dual three-dimensional non-gravitational QFT. We compute these correlators at
1-loop order for a theory containing massless scalars, fermions and gauge
fields, and present an extensive analysis of the constraints due to Ward
identities showing that they uniquely determine the correlators up to a few
constants. We define shapes for all cosmological bispectra and compare the
holographic shapes to the slow-roll ones, finding that some are distinguishable
while others, perhaps surprisingly, are not.Comment: 51pp; 4 fig
Tautomeric mutation: A quantum spin modelling
A quantum spin model representing tautomeric mutation is proposed for any DNA
molecule. Based on this model, the quantum mechanical calculations for
mutational rate and complementarity restoring repair rate in the replication
processes are carried out. A possible application to a real biological system
is discussed.Comment: 7 pages (no figures
LUNASKA experiments using the Australia Telescope Compact Array to search for ultra-high energy neutrinos and develop technology for the lunar Cherenkov technique
We describe the design, performance, sensitivity and results of our recent
experiments using the Australia Telescope Compact Array (ATCA) for lunar
Cherenkov observations with a very wide (600 MHz) bandwidth and nanosecond
timing, including a limit on an isotropic neutrino flux. We also make a first
estimate of the effects of small-scale surface roughness on the effective
experimental aperture, finding that contrary to expectations, such roughness
will act to increase the detectability of near-surface events over the neutrino
energy-range at which our experiment is most sensitive (though distortions to
the time-domain pulse profile may make identification more difficult). The aim
of our "Lunar UHE Neutrino Astrophysics using the Square Kilometer Array"
(LUNASKA) project is to develop the lunar Cherenkov technique of using
terrestrial radio telescope arrays for ultra-high energy (UHE) cosmic ray (CR)
and neutrino detection, and in particular to prepare for using the Square
Kilometer Array (SKA) and its path-finders such as the Australian SKA
Pathfinder (ASKAP) and the Low Frequency Array (LOFAR) for lunar Cherenkov
experiments.Comment: 27 pages, 18 figures, 4 tables
On graviton non-Gaussianities during inflation
We consider the most general three point function for gravitational waves
produced during a period of exactly de Sitter expansion. The de Sitter
isometries constrain the possible shapes to only three: two preserving parity
and one violating parity. These isometries imply that these correlation
functions should be conformal invariant. One of the shapes is produced by the
ordinary gravity action. The other shape is produced by a higher derivative
correction and could be as large as the gravity contribution. The parity
violating shape does not contribute to the bispectrum [1106.3228, 1108.0175],
even though it is present in the wavefunction. We also introduce a spinor
helicity formalism to describe de Sitter gravitational waves with circular
polarization. These results also apply to correlation functions in Anti-de
Sitter space. They also describe the general form of stress tensor correlation
functions, in momentum space, in a three dimensional conformal field theory.
Here all three shapes can arise, including the parity violating one.Comment: 51 pages, v2: Corrected statement about parity violation in the
gravitational wave bispectrum. Some other changes and references adde
Naked shell singularities on the brane
By utilizing non-standard slicings of 5-dimensional Schwarzschild and
Schwarzschild-AdS manifolds based on isotropic coordinates, we generate static
and spherically symmetric braneworld spacetimes containing shell-like naked
null singularities. For planar slicings, we find that the brane-matter sourcing
the solution is a perfect fluid with an exotic equation of state and a pressure
singularity where the brane crosses the bulk horizon. From a relativistic point
of view, such a singularity is required to maintain matter infinitesimally
above the surface of a black hole. From the point of view of the AdS/CFT
conjecture, the singular horizon can be seen as one possible quantum correction
to a classical black hole geometry. Various generalizations of planar slicings
are also considered for a Ricci-flat bulk, and we find that singular horizons
and exotic matter distributions are common features.Comment: REVTeX4, 13 pages, 6 figures, references and comments adde
Chord distribution functions of three-dimensional random media: Approximate first-passage times of Gaussian processes
The main result of this paper is a semi-analytic approximation for the chord
distribution functions of three-dimensional models of microstructure derived
from Gaussian random fields. In the simplest case the chord functions are
equivalent to a standard first-passage time problem, i.e., the probability
density governing the time taken by a Gaussian random process to first exceed a
threshold. We obtain an approximation based on the assumption that successive
chords are independent. The result is a generalization of the independent
interval approximation recently used to determine the exponent of persistence
time decay in coarsening. The approximation is easily extended to more general
models based on the intersection and union sets of models generated from the
iso-surfaces of random fields. The chord distribution functions play an
important role in the characterization of random composite and porous
materials. Our results are compared with experimental data obtained from a
three-dimensional image of a porous Fontainebleau sandstone and a
two-dimensional image of a tungsten-silver composite alloy.Comment: 12 pages, 11 figures. Submitted to Phys. Rev.
Choosing among residential options: Results of a vignette experiment
Older people who experience declining health are often faced with difficult decisions about possible residential relocation. The research aim was to determine how five distinct dimensions-functional status, features of current housing, social networks, features of retirement communities, and financial considerations-affect decisions to relocate to a retirement community. A vignette experiment with a factorial design was conducted involving both older people and adult children who were concerned with an aging parent. Use of the Internet for administration of the experiment made it possible to deliver information to research participants through video clips. Research participants were influenced by each of the dimensions; however, functional status of the vignette persons had the greatest impact, and financial considerations the least. Adult children were more likely to recommend moves than were older people. The research is suggestive of the potential for use of vignette experiments for a fuller understanding of relocation decisions
Using the internet to administer more realistic vignette experiments
This article illustrates an innovative method of administering stated choice studies (or vignette experiments) using computers and the Internet. The use of video clips to deliver information to research participants makes vignettes more realistic, helps to engage interest of research participants, and can reduce framing effects. The method also provides research participants with interactive options before making judgments. A study to determine the views of older people regarding residential options is used to illustrate the method. Even older people with limited experience in using computers participated successfully. The study findings showed that research participants responded both to the audiovisual characteristics of vignette persons and to the variables in the vignette structure
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