* Astronomy

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RE: BICEP2 experiment

Blobrana · L

Title: BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
Author: P. A. R. Ade (1), Z. Ahmed (2), R. W. Aikin (3), K. D. Alexander (4), D. Barkats (5), S. J. Benton (6), C. A. Bischoff (4), J. J. Bock (3,7), J. A. Brevik (3), I. Buder (4), E. Bullock (8), V. Buza (4), J. Connors (4), B. P. Crill (3,7), C. D. Dowell (7), C. Dvorkin (4), L. Duband (9), J. P. Filippini (3,10), S. Fliescher (11), S. R. Golwala (3), M. Halpern (12), M. Hasselfield (12), S. R. Hildebrandt (3,7), G. C. Hilton (13), V. V. Hristov (3), H. Hui (3), K. D. Irwin (2,13,14), K. S. Karkare (4), J. P. Kaufman (15), B. G. Keating (15), S. Kefeli (3), S. A. Kernasovskiy (2), J. M. Kovac (4), C. L. Kuo (2,14), E. M. Leitch (16,17), M. Lueker (3), P. Mason (3), K. G. Megerian (7), C. B. Netterfield (6,18), H. T. Nguyen (7), R. O'Brient (7), R. W. Ogburn IV (2,14), A. Orlando (15), C. Pryke (11,8), et al. (15 additional authors not shown)

The Keck Array is a system of cosmic microwave background (CMB) polarimeters, each similar to the BICEP2 experiment. In this paper we report results from the 2012 and 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as BICEP2. We again find an excess of B-mode power over the lensed-Lambda CDM expectation of >5 sigma in the range 30<\ell<150 and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with BICEP2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 K arcmin) over an effective area of 400 deg² for an equivalent survey weight of 250,000 K^-2. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of >6 sigma.

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Scientists abandon highly publicized claim about cosmic find

Scientists who made headlines last March by announcing that they'd found long-sought evidence about the early universe are now abandoning that claim.
New data show that their cosmic observations no longer back up that conclusion, they say.
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Leak suggests big bang find was a dusty mistake

Last year's big bang breakthrough has finally bitten the dust. In March last year, researchers using a telescope called BICEP2 at the South Pole made a splash when they claimed to have discovered primordial gravitational waves, a signal from the very early universe.
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Cosmic inflation: Leak suggests BICEP detection was wrong

Scientists who claimed last year to have found a pattern in the sky left by the super-rapid expansion of space just fractions of a second after the Big Bang were mistaken.
The signal had been confounded by light emission from dust in our own galaxy.
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Title: Planck intermediate results. XXX. The angular power spectrum of polarised dust emission at intermediate and high Galactic latitudes
Author: Planck Collaboration: R. Adam, P. A. R. Ade, N. Aghanim, M. Arnaud, J. Aumont, C. Baccigalupi, A. J. Banday, R. B. Barreiro, J. G. Bartlett, N. Bartolo, E. Battaner, K. Benabed, A. Benoit-Lévy, J.-P. Bernard, M. Bersanelli, P. Bielewicz, A. Bonaldi, L. Bonavera, J. R. Bond, J. Borrill, F. R. Bouchet, F. Boulanger, A. Bracco, M. Bucher, C. Burigana, R. C. Butler, E. Calabrese, J.-F. Cardoso, A. Catalano, A. Challinor, A. Chamballu, R.-R. Chary, H. C. Chiang, P. R. Christensen, D. L. Clements, S. Colombi, L. P. L. Colombo, C. Combet, F. Couchot, A. Coulais, A. Curto, F. Cuttaia, L. Danese, R. D. Davies, R. J. Davis, P. de Bernardis, G. de Zotti, J. Delabrouille, J.-M. Delouis, F.-X. Désert, C. Dickinson, J. M. Diego, K. Dolag, H. Dole, S. Donzelli, O. Doré, M. Douspis, A. Ducout, et al. (171 additional authors not shown)

The polarised thermal emission from Galactic dust is the main foreground present in measurements of the polarisation of the cosmic microwave background (CMB) at frequencies above 100GHz. We exploit the Planck HFI polarisation data from 100 to 353GHz to measure the dust angular power spectra C^EE,BBl over the range 40<l<600. These will bring new insights into interstellar dust physics and a precise determination of the level of contamination for CMB polarisation experiments. We show that statistical properties of the emission can be characterised over large fractions of the sky using Cl. For the dust, they are well described by power laws in l with exponents alpha^EE,BB=-2.42±0.02. The amplitudes of the polarisation Cl vary with the average brightness in a way similar to the intensity ones. The dust polarisation frequency dependence is consistent with modified blackbody emission with Beta_d=1.59 and T_d=19.6K. We find a systematic ratio between the amplitudes of the Galactic B- and E-modes of 0.5. We show that even in the faintest dust-emitting regions there are no "clean" windows where primordial CMB B-mode polarisation could be measured without subtraction of dust emission. Finally, we investigate the level of dust polarisation in the BICEP2 experiment field. Extrapolation of the Planck 353GHz data to 150GHz gives a dust power l(l+1)CBBl/(2pi) of 1.32 x 10^-²K²_CMB over the 40< l<120 range; the statistical uncertainty is ±0.29 and there is an additional uncertainty (+0.28,-0.24) from the extrapolation, both in the same units. This is the same magnitude as reported by BICEP2 over this l range, which highlights the need for assessment of the polarised dust signal. The present uncertainties will be reduced through an ongoing, joint analysis of the Planck and BICEP2 data sets.

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Title: Tensors, BICEP2, prior dependence, and dust
Author: Marina Cortês, Andrew R Liddle, David Parkinson

We investigate the prior dependence on the inferred spectrum of primordial tensor perturbations, in light of recent results from BICEP2 and taking into account a possible dust contribution to polarised anisotropies. We highlight an optimised parameterisation of the tensor power spectrum, and adoption of a logarithmic prior on its amplitude AT, leading to results that transform more evenly under change of pivot scale. In the absence of foregrounds the tension between the results of BICEP2 and Planck drives the tensor spectral index nT to be blue-tilted in a joint analysis, which would be in contradiction to the standard inflation prediction (nT<0). When foregrounds are accounted for, the BICEP2 results no longer require non-standard inflationary parameter regions. We present limits on primordial AT and nT, adopting foreground scenarios put forward by Mortonson & Seljak and motivated by Planck 353 GHz observations, and assess what dust contribution leaves a detectable cosmological signal. We find that if there is sufficient dust for the signal to be compatible with standard inflation, then the primordial signal is too weak to be robustly detected by BICEP2 if Planck+WMAP upper limits from temperature and E-mode polarisation are correct.

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Cosmic inflation: BICEP 'underestimated' dust problem

In a paper published on the arXiv pre-print server, Planck's researchers find that the part of the sky being observed by the BICEP team contained significantly more dust than it had assumed.
This new information does not mean the original claim is now dead. Not immediately, anyway.
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Blobrana · L

As time passed, however, and folks had time to digest some of the details presented by the BICEP2 team, there has been a growing unease about the possibility that the measurements may have been misinterpreted. The problem - the Achilles Heel of BICEP, so to speak - is that it operates at a single frequency, 150 GHz. That means that it is not possible for this experiment on its own to determine the spectrum of the detected signal
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Title: Toward an Understanding of Foreground Emission in the BICEP2 Region
Author: Raphael Flauger, J. Colin Hill, David N. Spergel

BICEP2 has reported the detection of a degree-scale B-mode polarisation pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyse the BICEP2 results and show that the 100x150 GHz and 150x150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarisation signal. We give independent estimates of the dust polarisation signal in the BICEP2 region using four different approaches. While these approaches are consistent with each other, the expected amplitude of the dust polarisation power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarisation angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin.

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Title: Simple Inflationary Models in Light of BICEP2: an Update
Author: Nobuchika Okada, Vedat Nefer Senoguz, Qaisar Shafi

The BICEP2 (CMB polarimeter) experiment has recently announced the discovery of inflationary gravitational waves in the B-mode power spectrum, with the tensor to scalar ratio r = 0.20+0.07-0.05. If confirmed, this provides a tremendous boost for a class of inflationary models in which the energy scale during inflation is on the order of 10^16 GeV. Inspired by this discovery, we provide an update on five relatively well motivated inflationary models in which the inflaton is a Standard Model singlet scalar field. These include i) the textbook quadratic and quartic potential models but with additional couplings of the inflaton to fermions and bosons, which enable reheating and also modify the naive predictions for the scalar spectral index n_s and r, ii) models with Higgs and Coleman-Weinberg potentials, and finally iii) a quartic potential model with non-minimal coupling of the inflaton to gravity. For n_s values close to 0.96, as determined by the WMAP9 and Planck experiments, the all-important parameter r in these models is nicely compatible with the BICEP2 measurements. The running of the scalar spectral index, quantified by |dn_s/dlnk|, is predicted in these models to be of order 10^-4-10^-3.

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