642 research outputs found
Are Compact Hyperbolic Models Observationally Ruled Out?
We revisit the observational constraints on compact(closed) hyperbolic(CH)
models from cosmic microwave background(CMB). We carry out Bayesian analyses
for CH models with volume comparable to the cube of the present curvature
radius using the COBE-DMR data and show that a slight suppression in the
large-angle temperature correlations owing to the non-trivial topology explains
rather naturally the observed anomalously low quadrupole which is incompatible
with the prediction of the standard infinite Friedmann-Robertson-Walker models.
While most of positions and orientations are ruled out, the likelihoods of CH
models are found to be much better than those of infinite counterparts for some
specific positions and orientations of the observer, leading to less stringent
constraints on the volume of the manifolds. Even if the spatial geometry is
nearly flat as , suppression of the angular power on
large angular scales is still prominent for CH models with volume much less
than the cube of the present curvature radius if the cosmological constant is
dominant at present.Comment: 25 pages, 16 EPS figures Version accepted for publication in PT
Systematic errors in cosmic microwave background polarization measurements
We investigate the impact of instrumental systematic errors on the potential
of cosmic microwave background polarization experiments targeting primordial
B-modes. To do so, we introduce spin-weighted Muller matrix-valued fields
describing the linear response of the imperfect optical system and receiver,
and give a careful discussion of the behaviour of the induced systematic
effects under rotation of the instrument. We give the correspondence between
the matrix components and known optical and receiver imperfections, and compare
the likely performance of pseudo-correlation receivers and those that modulate
the polarization with a half-wave plate. The latter is shown to have the
significant advantage of not coupling the total intensity into polarization for
perfect optics, but potential effects like optical distortions that may be
introduced by the quasi-optical wave plate warrant further investigation. A
fast method for tolerancing time-invariant systematic effects is presented,
which propagates errors through to power spectra and cosmological parameters.
The method extends previous studies to an arbitrary scan strategy, and
eliminates the need for time-consuming Monte-Carlo simulations in the early
phases of instrument and survey design. We illustrate the method with both
simple parametrized forms for the systematics and with beams based on
physical-optics simulations. Example results are given in the context of
next-generation experiments targeting tensor-to-scalar ratios r ~ 0.01.Comment: 19 pages, 7 figures; Minor changes to match version accepted by MNRA
The shape of the CMB lensing bispectrum
Lensing of the CMB generates a significant bispectrum, which should be
detected by the Planck satellite at the 5-sigma level and is potentially a
non-negligible source of bias for f_NL estimators of local non-Gaussianity. We
extend current understanding of the lensing bispectrum in several directions:
(1) we perform a non-perturbative calculation of the lensing bispectrum which
is ~10% more accurate than previous, first-order calculations; (2) we
demonstrate how to incorporate the signal variance of the lensing bispectrum
into estimates of its amplitude, providing a good analytical explanation for
previous Monte-Carlo results; and (3) we discover the existence of a
significant lensing bispectrum in polarization, due to a previously-unnoticed
correlation between the lensing potential and E-polarization as large as 30% at
low multipoles. We use this improved understanding of the lensing bispectra to
re-evaluate Fisher-matrix predictions, both for Planck and cosmic variance
limited data. We confirm that the non-negligible lensing-induced bias for
estimation of local non-Gaussianity should be robustly treatable, and will only
inflate f_NL error bars by a few percent over predictions where lensing effects
are completely ignored (but note that lensing must still be accounted for to
obtain unbiased constraints). We also show that the detection significance for
the lensing bispectrum itself is ultimately limited to 9 sigma by cosmic
variance. The tools that we develop for non-perturbative calculation of the
lensing bispectrum are directly relevant to other calculations, and we give an
explicit construction of a simple non-perturbative quadratic estimator for the
lensing potential and relate its cross-correlation power spectrum to the
bispectrum. Our numerical codes are publicly available as part of CAMB and
LensPix.Comment: 32 pages, 10 figures; minor changes to match JCAP-accepted version.
CMB lensing and primordial local bispectrum codes available as part of CAMB
(http://camb.info/
Effective equations of motion and initial conditions for inflation in quantum cosmology
We obtain effective equations of inflationary dynamics for the mean inflaton
and metric fields in the no-boundary and tunneling quantum states of the
Universe. In the slow roll approximation (taking the form of the local
Schwiger-DeWitt expansion) effective equations follow from the Euclidean
effective action on the DeSitter gravitational instanton. Effective equations
are applied in the model of the inflaton scalar field coupled to the GUT sector
of matter fields and also having a strong nonminimal coupling to the curvature.
The inverse of its big negative nonminimal coupling constant, serves as a small
parameter of the slow roll expansion and semiclassical expansion of quantum
gravitational effects. As a source of initial conditions we use a sharp
probability peak recently obtained in the one-loop approximation for the
no-boundary and tunneling quantum states and belonging (in virtue of a strong
nonminimal coupling) to the GUT energy scale much below the Planck scale. The
obtained equations in the tunneling quantum state predict a finite duration of
inflationary stage compatible with the observational status of inflation
theory, whereas for the no-boundary state they lead to the infinite
inflationary epoch with a constant inflaton field.Comment: 23 pages, LaTe
Detectability of Microwave Background Polarization
[NOTE: Previous versions of this paper (both on astro-ph and published in
Phys. Rev. D) contain results that are in error. The power spectra C_l were
normalized incorrectly by a factor of 2 pi. All observing times in
detector-years in those versions are too large by a factor of 2 pi. The main
place these numbers appear is on the vertical axes of Figures 4 and 5. Note
that because all calculations were based on the same power spectra, all
conclusions pertaining to comparisons of different techniques remain unchanged.
This error has been corrected in the present version of the paper. An erratum
is being sent to Phys. Rev. D. I apologize for the error.]
Using a Fisher-matrix formalism, we calculate the required sensitivities and
observing times for an experiment to measure the amplitudes of both E and B
components as a function of sky coverage, taking full account of the fact that
the two components cannot be perfectly separated in an incomplete sky map. We
also present a simple approximation scheme that accounts for mixing of E and B
components in computing predicted errors in the E-component power spectrum
amplitude. In an experiment with small sky coverage, mixing of the two
components increases the difficulty of detecting the subdominant B component by
a factor of two or more in observing time; however, for larger survey sizes the
effect of mixing is less pronounced. Surprisingly, mixing of E and B components
can enhance the detectability of the E component by increasing the effective
number of independent modes that probe this componentComment: Previous versions of this paper contained results that were in error.
The present version on astro-ph has been corrected, and an erratum is being
submitted. See abstract for detail
Quantification of the performance of iterative and non-iterative computational methods of locating partial discharges using RF measurement techniques
Partial discharge (PD) is an electrical discharge phenomenon that occurs when the insulation materialof high voltage equipment is subjected to high electric field stress. Its occurrence can be an indication ofincipient failure within power equipment such as power transformers, underground transmission cableor switchgear. Radio frequency measurement methods can be used to detect and locate discharge sourcesby measuring the propagated electromagnetic wave arising as a result of ionic charge acceleration. Anarray of at least four receiving antennas may be employed to detect any radiated discharge signals, thenthe three dimensional position of the discharge source can be calculated using different algorithms. These algorithms fall into two categories; iterative or non-iterative. This paper evaluates, through simulation, the location performance of an iterative method (the standardleast squares method) and a non-iterative method (the Bancroft algorithm). Simulations were carried outusing (i) a "Y" shaped antenna array and (ii) a square shaped antenna array, each consisting of a four-antennas. The results show that PD location accuracy is influenced by the algorithm's error bound, thenumber of iterations and the initial values for the iterative algorithms, as well as the antenna arrangement for both the non-iterative and iterative algorithms. Furthermore, this research proposes a novel approachfor selecting adequate error bounds and number of iterations using results of the non-iterative method, thus solving some of the iterative method dependencies
Observational Constraints on Open Inflation Models
We discuss observational constraints on models of open inflation. Current
data from large-scale structure and the cosmic microwave background prefer
models with blue spectra and/or Omega_0 >= 0.3--0.5. Models with minimal
anisotropy at large angles are strongly preferred.Comment: 4 pages, RevTeX, with 2 postscript figures included. Second Figure
correcte
Characterization of two receptors for TRAIL.
Two receptors for TRAIL, designated TRAIL-R2 and TRAIL-R3, have been identified. Both are members of the tumor necrosis factor receptor family. TRAIL-R2 is structurally similar to the death-domain-containing receptor TRAIL-R1 (DR-4), and is capable of inducing apoptosis. In contrast, TRAIL-R3 does not promote cell death. TRAIL-R3 is highly glycosylated and is membrane bound via a putative phosphatidylinositol anchor. The extended structure of TRAIL-R3 is due to the presence of multiple threonine-, alanine-, proline- and glutamine-rich repeats (TAPE repeats). TRAIL-R2 shows a broad tissue distribution, whereas the expression of TRAIL-R3 is restricted to peripheral blood lymphocytes (PBLs) and skeletal muscle. All three TRAIL receptors bind TRAIL with similar affinity, suggesting a complex regulation of TRAIL-mediated signals
Analysis of CMB polarization on an incomplete sky
The full sky cosmic microwave background polarization field can be decomposed
into 'electric' and 'magnetic' components. Working in harmonic space we
construct window functions that allow clean separation of the electric and
magnetic modes from observations over only a portion of the sky. Our
construction is exact for azimuthally symmetric patches, but should continue to
perform well for arbitrary patches. From the window functions we obtain
variables that allow for robust estimation of the magnetic component without
risk of contamination from the probably much larger electric signal. For
isotropic, uncorrelated noise the variables have a very simple diagonal noise
correlation, and further analysis using them should be no harder than analysing
the temperature field. For an azimuthally-symmetric patch, such as that
obtained from survey missions when the galactic region is removed, the
exactly-separated variables are fast to compute allowing us to estimate the
magnetic signal that could be detected by the Planck satellite in the absence
of non-galactic foregrounds. We also discuss the sensitivity of future
experiments to tensor modes in the presence of a magnetic signal generated by
weak lensing, and give lossless methods for analysing the electric polarization
field in the case that the magnetic component is negligible.Comment: 27 pages, 8 figures. New appendix on weak signal detection and
revised plots using a better statistic. Other changes to match version
accepted by PRD. Sample source code now available at
http://cosmologist.info/pola
Forecasting neutrino masses from galaxy clustering in the Dark Energy Survey combined with the Planck Measurements
We study the prospects for detecting neutrino masses from the galaxy angular
power spectrum in photometric redshift shells of the Dark Energy Survey (DES)
over a volume of 20 (Gpc/h)^3 combined with the Cosmic Microwave Background
(CMB) angular fluctuations expected to be measured from the Planck satellite.
We find that for a Lambda-CDM concordance model with 7 free parameters in
addition to a fiducial neutrino mass of M_nu = 0.24 eV, we recover from DES
&Planck the correct value with uncertainty of +- 0.12 eV (95 % CL), assuming
perfect knowledge of the galaxy biasing. If the fiducial total mass is close to
zero, then the upper limit is 0.11 eV (95 % CL). This upper limit from DES
&Planck is over 3 times tighter than using Planck alone, as DES breaks the
parameter degeneracies in a CMB-only analysis. The analysis utlilizes spherical
harmonics up to 300, averaged in bin of 10 to mimic the DES sky coverage. The
results are similar if we supplement DES bands (grizY) with the VISTA
Hemisphere Survey (VHS) near infrared band (JHK). The result is robust to
uncertainties in non-linear fluctuations and redshift distortions. However, the
result is sensitive to the assumed galaxy biasing schemes and it requires
accurate prior knowledge of the biasing. To summarize, if the total neutrino
mass in nature greater than 0.1eV, we should be able to detect it with DES
&Planck, a result with great importance to fundamental Physics.Comment: Submitted to MNRAS, 9 pages, 10 figure
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