5,591 research outputs found
Cascading Cosmology
We develop a fully covariant, well-posed 5D effective action for the 6D
cascading gravity brane-world model, and use this to study cosmological
solutions. We obtain this effective action through the 6D decoupling limit, in
which an additional scalar degree mode, \pi, called the brane-bending mode,
determines the bulk-brane gravitational interaction. The 5D action obtained
this way inherits from the sixth dimension an extra \pi self-interaction
kinetic term. We compute appropriate boundary terms, to supplement the 5D
action, and hence derive fully covariant junction conditions and the 5D
Einstein field equations. Using these, we derive the cosmological evolution
induced on a 3-brane moving in a static bulk. We study the strong- and
weak-coupling regimes analytically in this static ansatz, and perform a
complete numerical analysis of our solution. Although the cascading model can
generate an accelerating solution in which the \pi field comes to dominate at
late times, the presence of a critical singularity prevents the \pi field from
dominating entirely. Our results open up the interesting possibility that a
more general treatment of degravitation in a time-dependent bulk, or taking
into account finite brane-thickness effects, may lead to an accelerating
universe without a cosmological constant.Comment: [v2] 27 pages, 2 figures, corrected typos, expanded discussion of
late-time cosmological behavio
Cascading Gravity is Ghost Free
We perform a full perturbative stability analysis of the 6D cascading gravity
model in the presence of 3-brane tension. We demonstrate that for sufficiently
large tension on the (flat) 3-brane, there are no ghosts at the perturbative
level, consistent with results that had previously only been obtained in a
specific 5D decoupling limit. These results establish the cascading gravity
framework as a consistent infrared modification of gravity.Comment: 24 pages, minor changes, argument on vector perturbations improve
qPCR multiplex detection of microRNA and messenger RNA in a single reaction.
Reverse Transcription-Quantitative PCR (RT-qPCR) is one of the standards for analytical measurement of different RNA species in biological models. However, current Reverse Transcription (RT) based priming strategies are unable to synthesize differing RNAs and ncRNAs especially miRNAs, within a single tube. We present a new methodology, referred to as RNAmp, that measures in parallel miRNA and mRNA expression. We demonstrate this in various cell lines, then evaluate clinical utility by quantifying several miRNAs and mRNA simultaneously in sera. PCR efficiency in RNAmp was estimated between 1.8 and 1.9 which is comparable to standard miRNA and random primer RT approaches. Furthermore, when using RNAmp to detect selected mRNA and miRNAs, the quantification cycle (Cq) was several cycles lower. This low volume single-tube duplex protocol reduces technical variation and reagent usage and is suitable for uniform analysis of single or multiple miRNAs and/or mRNAs within a single qPCR reaction
Weighing Neutrinos with Galaxy Cluster Surveys
Large future galaxy cluster surveys, combined with cosmic microwave
background observations, can achieve a high sensitivity to the masses of
cosmologically important neutrinos. We show that a weak lensing selected sample
of ~100,000 clusters could tighten the current upper bound on the sum of masses
of neutrino species by an order of magnitude, to a level of 0.03 eV. Since this
statistical sensitivity is below the best existing lower limit on the mass of
at least one neutrino species, a future detection is likely, provided that
systematic errors can be controlled to a similar level.Comment: 4 pages, 1 figure, version accepted for publication in PR
Density Perturbations in the Ekpyrotic Scenario
We study the generation of density perturbations in the ekpyrotic scenario
for the early universe, including gravitational backreaction. We expose
interesting subtleties that apply to both inflationary and ekpyrotic models.
Our analysis includes a detailed proposal of how the perturbations generated in
a contracting phase may be matched across a `bounce' to those in an expanding
hot big bang phase. For the physical conditions relevant to the ekpyrotic
scenario, we re-obtain our earlier result of a nearly scale-invariant spectrum
of energy density perturbations. We find that the perturbation amplitude is
typically small, as desired to match observation.Comment: 36 pages, compressed and RevTex file, one postscript figure file.
Minor typographical and numerical errors corrected, discussion added. This
version to appear in Physical Review
Cascading DGP
We present a higher codimension generalization of the DGP scenario which,
unlike previous attempts, is free of ghost instabilities. The 4D propagator is
made regular by embedding our visible 3-brane within a 4-brane, each with their
own induced gravity terms, in a flat 6D bulk. The model is ghost-free if the
tension on the 3-brane is larger than a certain critical value, while the
induced metric remains flat. The gravitational force law `cascades' from a 6D
behavior at the largest distances followed by a 5D and finally a 4D regime at
the shortest scales.Comment: 4 pages; one reference added and a typo correcte
The IR-Completion of Gravity: What happens at Hubble Scales?
We have recently proposed an "Ultra-Strong" version of the Equivalence
Principle (EP) that is not satisfied by standard semiclassical gravity. In the
theory that we are conjecturing, the vacuum expectation value of the (bare)
energy momentum tensor is exactly the same as in flat space: quartically
divergent with the cut-off and with no spacetime dependent (subleading) ter ms.
The presence of such terms seems in fact related to some known difficulties,
such as the black hole information loss and the cosmological constant problem.
Since the terms that we want to get rid of are subleading in the high-momentum
expansion, we attempt to explore the conjectured theory by "IR-completing" GR.
We consider a scalar field in a flat FRW Universe and isolate the first
IR-correction to its Fourier modes operators that kills the quadratic (next to
leading) time dependent divergence of the stress energy tensor VEV. Analogously
to other modifications of field operators that have been proposed in the
literature (typically in the UV), the present approach seems to suggest a
breakdown (here, in the IR, at large distances) of the metric manifold
description. We show that corrections to GR are in fact very tiny, become
effective at distances comparable to the inverse curvature and do not contain
any adjustable parameter. Finally, we derive some cosmological implications. By
studying the consistency of the canonical commutation relations, we infer a
correction to the distance between two comoving observers, which grows as the
scale factor only when small compared to the Hubble length, but gets relevant
corrections otherwise. The corrections to cosmological distance measures are
also calculable and, for a spatially flat matter dominated Universe, go in the
direction of an effective positive acceleration.Comment: 27 pages, 2 figures. Final version, references adde
Expression of microRNAs in HPV negative tonsil cancers and their regulation of PDCD4
© 2016. Global rates of tonsil cancer have been increasing since the turn of the millennia, however we still have a limited understanding of the genes and pathways which control this disease. This array dataset which is linked to our publication (Zhang et al., 2015) describes the profiling of human miRNAs in tonsil and normal adjacent tissues. With this dataset, we identified a list of microRNA (miRNA) which were highly over represented in tonsil cancers and showed that several miRNAs were able to regulate the tumour suppressor PDCD4 in a temporal manner. The dataset has been deposited into Gene Expression Omnibus (GSE75630)
A PRELIMINARY ELECTROMYOGRAPHIC INVESTIGATION INTO SHOULDER MUSCLE ACTIVITY IN CRICKET SEAM BOWLING
2 The aim of this investigation was to describe and compare surface electromyographic activity of shoulder musculature during cricket seam bowling between two elite bowlers with (bowler A) and without (bowler B) shoulder pathology. Activity of seven muscles were recorded at 500 Hz with a digital camera sampling at 210 Hz used to define phases within the movement. Whilst both the duration of the movement and ball velocity were similar between bowlers (bowler A: duration = 0.89 ± 0.04 s, ball velocity = 27.08 ± 1.21 m.s-1; bowler B: duration = 0.72 ± 0.02 s, ball velocity = 26.59 ± 1.49 m.s-1), variations in muscle activity particularly for biceps brachii and infraspinatus were established. Further research utilising larger sample sizes is required to establish if such variations occur as a consequence of shoulder pathology or if these are due to other contributing factors
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