* Astronomy

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RE: BICEP2 experiment

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Title: The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?
Author: Kevork N. Abazajian, Grigor Aslanyan, Richard Easther, Layne C. Price

An inflationary gravitational wave background consistent with BICEP2 is difficult to reconcile with a simple power-law spectrum of primordial scalar perturbations. Tensor modes contribute to the temperature anisotropies at multipoles with l\lesssim 100, and this effect --- together with a prior on the form of the scalar perturbations --- was the source of previous bounds on the tensor-to-scalar ratio. We compute Bayesian evidence for combined fits to BICEP2 and Planck for three nontrivial primordial spectra: a) a running spectral index, b) a cutoff at fixed wavenumber, and c) a spectrum described by a linear spline with a single internal knot. We find no evidence for a cutoff, weak evidence for a running index, and significant evidence for a "broken" spectrum. Taken at face-value, the BICEP2 results require two new inflationary parameters in order to describe both the broken scale invariance in the perturbation spectrum and the observed tensor-to-scalar ratio. Alternatively, this tension may be resolved by additional data and more detailed analyses.

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Title: Did BICEP2 see vector modes? First B-mode constraints on cosmic defects
Author: Adam Moss, Levon Pogosian

Scaling networks of cosmic defects, such as strings and textures, actively generate scalar, vector and tensor metric perturbations throughout the history of the universe. In particular, vector modes sourced by defects are an efficient source of the CMB B-mode polarization. We use the recently released BICEP2 and POLARBEAR CMB B-mode polarization spectra to constrain properties of a wide range of different types of cosmic strings networks. We find that in order for strings to provide a satisfactory fit on their own, the effective inter-string distance needs to be extremely large -- spectra that fit the data best are more representative of global strings and textures. When a local string contribution is considered together with the inflationary B-mode spectrum, the fit is improved. We discuss implications of these results for theories that predict cosmic defects.

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Title: The challenge for single field inflation with BICEP2 result
Author: Yungui Gong

The detection of B-mode power spectrum by the BICEP2 collaboration constrains the tensor-to-scalar ratio r=0.20^{+0.07}_{-0.05} for the lensed-\LambdaCDM model. The consistency of this big value with the Planck results require a large running of the spectral index. The large values of the tensor-to-scalar ratio and the running of the spectral index put a challenge to single field inflation. For the chaotic inflation, the larger the value of the tensor-to-scalar ratio is, the smaller the value of running of the spectral index is. For the nature inflation, the absolute value of the running of the spectral index has an upper limit.

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Title: BICEP2 II: Experiment and Three-Year Data Set
Author: BICEP2 Collaboration: P. A. R Ade (1), R. W. Aikin (2), M. Amiri (3), D. Barkats (4), S. J. Benton (5), C. A. Bischoff (6), J. J. Bock (2,7), J. A. Brevik (2), I. Buder (6), E. Bullock (8), G. Davis (3), C. D. Dowell (7), L. Duband (9), J. P. Filippini (2), S. Fliescher (10), S. R. Golwala (2), M. Halpern (3), M. Hasselfield (3), S. R. Hildebrandt (2,7), G. C. Hilton (11), V. V. Hristov (2), K. D. Irwin (12,13,11), K. S. Karkare (6), J. P. Kaufman (14), B. G. Keating (14), S. A. Kernasovskiy (12), J. M. Kovac (6), C. L. Kuo (12,13), E. M. Leitch (15), N. Llombart (7), M. Lueker (2), C. B. Netterfield (5), H. T. Nguyen (7), R. O'Brient (7), R. W. Ogburn IV (12,13), A. Orlando (14), C. Pryke (10), C. D. Reintsema (11), S. Richter (6), R. Schwarz (10), C. D. Sheehy (10,15), Z. K. Staniszewski (2), et al. (9 additional authors not shown)

The BICEP2 instrument was designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 1 to 5 degrees (l=40-200), near the expected peak of the B-mode polarization signature of primordial gravitational waves from cosmic inflation. Measuring B-modes requires dramatic improvement in sensitivity combined with exquisite control of systematics. We have built on the successful strategy of BICEP1, which achieved the most sensitive limit on B-modes at these scales. The telescope had a 26 cm aperture and cold, on-axis, refractive optics, and it observed from a three-axis mount at the South Pole. BICEP2 adopted a new detector design in which beam-defining slot antenna arrays couple to transition-edge sensor (TES) bolometers, all fabricated monolithically on a common substrate. BICEP2 took advantage of this design's scalable fabrication and multiplexed SQUID readout to field more detectors than BICEP1, improving mapping speed by more than a factor of ten. In this paper we report on the design and performance of the instrument and on the three-year data set. BICEP2 completed three years of observation with 500 detectors at 150 GHz. After optimization of detector and readout parameters BICEP2 achieved an instrument noise equivalent temperature of 17.0 K sqrt(s) and the full data set reached Stokes Q and U map depths of 87.8 nK in square-degree pixels (5.3 K arcmin) over an effective area of 390.3 square degrees within a 1000 square degree field. These are the deepest CMB polarization maps at degree angular scales.

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Big bang scientist on a groundbreaking discovery - Newsnight

Spoiler

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Stephen Hawking on new Big Bang evidence

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Title: BICEP2 I: Detection Of B-mode Polarization at Degree Angular Scales
Author: BICEP2 Collaboration: P. A. R Ade (1), R. W. Aikin (2), D. Barkats (3), S. J. Benton (4), C. A. Bischoff (5), J. J. Bock (2,6), J. A. Brevik (2), I. Buder (5), E. Bullock (7), C. D. Dowell (6), L. Duband (8), J. P. Filippini (2), S. Fliescher (9), S. R. Golwala (2), M. Halpern (10), M. Hasselfield (10), S. R. Hildebrandt (2,6), G. C. Hilton (11), V. V. Hristov (2), K. D. Irwin (12,13,11), K. S. Karkare (5), J. P. Kaufman (14), B. G. Keating (14), S. A. Kernasovskiy (12), J. M. Kovac (5), C. L. Kuo (12,13), E. M. Leitch (15), M. Lueker (2), P. Mason (2), C. B. Netterfield (4), H. T. Nguyen (6), R. O'Brient (6), R. W. Ogburn IV (12,13), A. Orlando (14), C. Pryke (9,7), C. D. Reintsema (11), S. Richter (5), R. Schwarz (9), C. D. Sheehy (9,15), Z. K. Staniszewski (2,6), R. V. Sudiwala (1), et al. (6 additional authors not shown)

We report results from the BICEP2 experiment, a Cosmic Microwave Background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around l=80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor (TES) 150 GHz bolometers each with temperature sensitivity of approx. 300 uk.sqrt(s). BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square degrees was observed to a depth of 87 nK-degrees in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations and results. We find an excess of B-mode power over the base lensed-LCDM expectation in the range 30<l<150, inconsistent with the null hypothesis at a significance of >5\sigma. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. We also estimate potential foreground signals and find that available models predict these to be considerably smaller than the observed signal. These foreground models possess no significant cross-correlation with our maps. Additionally, cross-correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3\sigma significance and its spectral index is found to be consistent with that of the CMB, disfavoring synchrotron or dust at 2.3\sigma and 2.2\sigma, respectively. The observed B-mode power spectrum is well-fit by a lensed-LCDM + tensor theoretical model with tensor/scalar ratio r=0.20+0.07-0.05, with r=0 disfavored at 7.0\sigma. Subtracting the best available estimate for foreground dust modifies the likelihood slightly so that r=0 is disfavored at 5.9\sigma.

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