229 research outputs found
Multi-dimensional classical and quantum cosmology: Exact solutions, signature transition and stabilization
We study the classical and quantum cosmology of a -dimensional
spacetime minimally coupled to a scalar field and present exact solutions for
the resulting field equations for the case where the universe is spatially
flat. These solutions exhibit signature transition from a Euclidean to a
Lorentzian domain and lead to stabilization of the internal space, in contrast
to the solutions which do not undergo signature transition. The corresponding
quantum cosmology is described by the Wheeler-DeWitt equation which has exact
solutions in the mini-superspace, resulting in wavefunctions peaking around the
classical paths. Such solutions admit parametrizations corresponding to metric
solutions of the field equations that admit signature transition.Comment: 15 pages, two figures, to appear in JHE
Scales of the Extra Dimensions and their Gravitational Wave Backgrounds
Circumstances are described in which symmetry breaking during the formation
of our three-dimensional brane within a higher-dimensional space in the early
universe excites mesoscopic classical radion or brane-displacement degrees of
freedom and produces a detectable stochastic background of gravitational
radiation. The spectrum of the background is related to the unification energy
scale and the the sizes and numbers of large extra dimensions. It is shown that
properties of the background observable by gravitational-wave observatories at
frequencies Hz to Hz contain information about
unification on energy scales from 1 to TeV, gravity propagating
through extra-dimension sizes from 1 mm to mm, and the dynamical
history and stabilization of from one to seven extra dimensions.Comment: 6 pages, Latex, 1 figure, submitted to Phys. Re
Using VR to investigate the relationship between visual acuity and severity of simulated oscillopsia
Purpose: Oscillopsia is a debilitating symptom resulting from involuntary eye movement most commonly associated with acquired nystagmus. Investigating and documenting the efects of oscillopsia severity on visual acuity (VA) is challenging. This paper aims to further understanding of the efects of oscillopsia using a virtual reality simulation.
Methods: Fifteen right-beat horizontal nystagmus waveforms, with diferent amplitude (1°, 3°, 5°, 8° and 11°) and frequency (1.25 Hz, 2.5 Hz and 5 Hz) combinations, were produced and imported into virtual reality to simulate diferent severities of oscillopsia. Fifty participants without ocular pathology were recruited to read logMAR charts in virtual reality under stationary conditions (no oscillopsia) and subsequently while experiencing simulated oscillopsia. The change in VA (logMAR) was calculated for each oscillopsia simulation (logMAR VA with oscillopsia â logMAR VA with no oscillopsia), removing the inluence of diferent baseline VAs between participants. A one-tailed paired t-test was used to assess statistical signiicance in the worsening in VA caused by the oscillopsia simulations.
Results: VA worsened with each incremental increase in simulated oscillopsia intensity (frequency x amplitude), either by increasing frequency or amplitude, with the exception of statistically insigniicant changes at lower intensity simulations. Theoretical understanding predicted a linear relationship between increasing oscillopsia intensity and worsening VA. This was supported by observations at lower intensity simulations but not at higher intensities, with incremental changes in VA gradually levelling of. A potential reason for the diference at higher intensities is the inluence of frame rate when using digital simulations in virtual reality.
Conclusions: The frequency and amplitude were found to equally afect VA, as predicted. These results not only consolidate the assumption that VA degrades with oscillopsia but also provide quantitative information that relates these changes to amplitude and frequency of oscillopsia
Variable-Speed-of-Light Cosmology from Brane World Scenario
We argue that the four-dimensional universe on the TeV brane of the
Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat,
with gravitons traveling faster than photons instead, while the radion varies
with time. We show that such brane world bimetric model can thereby solve the
flatness and the cosmological constant problems, provided the speed of a
graviton decreases to the present day value rapidly enough. The resolution of
other cosmological problems such as the horizon problem and the monopole
problem requires supplementation by inflation, which may be achieved by the
radion field provided the radion potential satisfies the slow-roll
approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.
Stabilization of internal spaces in multidimensional cosmology
Effective 4-dimensional theories are investigated which were obtained under
dimensional reduction of multidimensional cosmological models with a minimal
coupled scalar field as matter source. Conditions for the internal space
stabilization are considered and the possibility for inflation in the external
space is discussed. The electroweak as well as the Planck fundamental scale
approaches are investigated and compared with each other. It is shown that
there exists a rescaling for the effective cosmological constant as well as for
gravitational exciton masses in the different approaches.Comment: 12 pages, LaTeX2e, to appear in Phys.Rev.D, note adde
Conformally Invariant Gauge Theory of 3-Branes in 6D and the Cosmological Constant
It is shown that the gauge theory of relativistic 3-Branes can be formulated
in a conformally invariant way if the embedding space is six-dimensional. The
implementation of conformal invariance requires the use of a modified measure,
independent of the metric in the action. Brane-world scenarios without the need
of a cosmological constant in 6D are constructed. Thus, no ``old'' cosmological
constant problem appears at this level.Comment: 12 pages, Latex, no figures; final version accepted for publication
in Phys.Rev. D; Sect.II expande
The Deformable Universe
The concept of smooth deformations of a Riemannian manifolds, recently
evidenced by the solution of the Poincar\'e conjecture, is applied to
Einstein's gravitational theory and in particular to the standard FLRW
cosmology. We present a brief review of the deformation of Riemannian geometry,
showing how such deformations can be derived from the Einstein-Hilbert
dynamical principle. We show that such deformations of space-times of general
relativity produce observable effects that can be measured by four-dimensional
observers. In the case of the FLRW cosmology, one such observable effect is
shown to be consistent with the accelerated expansion of the universe.Comment: 20 pages, LaTeX, 3 figure
Quantum self-consistency of brane models
Continuing on our previous work, we consider a class of higher dimensional
brane models with the topology of , where
is a one-parameter compact manifold and two branes of codimension 1 are located
at the orbifold fixed points. We consider a set-up where such a solution arises
from Einstein-Yang-Mills theory and evaluate the one-loop effective potential
induced by gauge fields and by a generic bulk scalar field. We show that this
type of brane models resolves the gauge hierarchy between the Planck and
electroweak scales through redshift effects due to the warp factor . The value of is then fixed by minimizing the effective potential. We
find that, as in the Randall Sundrum case, the gauge field contribution to the
effective potential stabilises the hierarchy without fine-tuning as long as the
laplacian on has a zero eigenvalue. Scalar fields can
stabilise the hierarchy depending on the mass and the non-minimal coupling. We
also address the quantum self-consistency of the solution, showing that the
classical brane solution is not spoiled by quantum effects.Comment: 10 page
Mini viral RNAs act as innate immune agonists during influenza virus infection
We thank the High-Throughput Genomics Group at the Wellcome Trust Centre for Human Genetics (funded by Wellcome Trust grant 090532/Z/09/Z) for the generation of adapter-ligated mvRNA sequencing data. This work was supported by the Wellcome Trust grant 098721/Z/12/Z, the joint Wellcome Trust and Royal Society grant 206579/Z/17/Z and a Netherlands Organization for Scientific Research (NWO) grant 825.11.029 to A.J.W.t.V.; EPA Cephalosporin Junior Research Fellowship to D.L.V.B.; support by the Intramural Research Program of NIAID, NIH, to E.d.W.; Research Grants Council of the Hong Kong Special Administrative Region, China, project no. T11-705/14N and a Croucher Senior Research Fellowship to L.L.M.P.; and Medical Research Council (MRC) programme grants MR/K000241/1 and MR/R009945/1 to E.F. and studentship to J.C.L.The molecular processes that determine the outcome of influenza virus infection in humans are multifactorial and involve a complex interplay between host, viral and bacterial factors1. However, it is generally accepted that a strong innate immune dysregulation known as âcytokine stormâ contributes to the pathology of infections with the 1918 H1N1 pandemic or the highly pathogenic avian influenza viruses of the H5N1 subtype2,3,4. The RNA sensor retinoic acid-inducible gene I (RIG-I) plays an important role in sensing viral infection and initiating a signalling cascade that leads to interferon expression5. Here, we show that short aberrant RNAs (mini viral RNAs (mvRNAs)), produced by the viral RNA polymerase during the replication of the viral RNA genome, bind to and activate RIG-I and lead to the expression of interferon-ÎČ. We find that erroneous polymerase activity, dysregulation of viral RNA replication or the presence of avian-specific amino acids underlie mvRNA generation and cytokine expression in mammalian cells. By deep sequencing RNA samples from the lungs of ferrets infected with influenza viruses, we show that mvRNAs are generated during infection in vivo. We propose that mvRNAs act as the main agonists of RIG-I during influenza virus infection.PostprintPeer reviewe
Non-Minimal Warm Inflation and Perturbations on the Warped DGP Brane with Modified Induced Gravity
We construct a warm inflation model with inflaton field non-minimally coupled
to induced gravity on a warped DGP brane. We incorporate possible modification
of the induced gravity on the brane in the spirit of -gravity. We study
cosmological perturbations in this setup. In the case of two field inflation
such as warm inflation, usually entropy perturbations are generated. While it
is expected that in the case of one field inflation these perturbations to be
removed, we show that even in the absence of the radiation field, entropy
perturbations are generated in our setup due to non-minimal coupling and
modification of the induced gravity.Comment: 29 pages, 7 figures, Accepted by Gen. Rel Gravi
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