397 research outputs found
Testable polarization predictions for models of CMB isotropy anomalies
Anomalies in the large-scale CMB temperature sky measured by WMAP have been
suggested as possible evidence for a violation of statistical isotropy on large
scales. In any physical model for broken isotropy, there are testable
consequences for the CMB polarization field. We develop simulation tools for
predicting the polarization field in models that break statistical isotropy
locally through a modulation field. We study two different models: dipolar
modulation, invoked to explain the asymmetry in power between northern and
southern ecliptic hemispheres, and quadrupolar modulation, posited to explain
the alignments between the quadrupole and octopole. For the dipolar case, we
show that predictions for the correlation between the first 10 multipoles of
the temperature and polarization fields can typically be tested at better than
the 98% CL. For the quadrupolar case, we show that the polarization quadrupole
and octopole should be moderately aligned. Such an alignment is a generic
prediction of explanations which involve the temperature field at recombination
and thus discriminate against explanations involving foregrounds or local
secondary anisotropy. Predicted correlations between temperature and
polarization multipoles out to l = 5 provide tests at the ~ 99% CL or stronger
for quadrupolar models that make the temperature alignment more than a few
percent likely. As predictions of anomaly models, polarization statistics move
beyond the a posteriori inferences that currently dominate the field.Comment: 17 pages, 15 figures; published in PRD; references adde
Stochastic and resolvable gravitational waves from ultralight bosons
Ultralight scalar fields around spinning black holes can trigger superradiant instabilities, forming a long-lived bosonic condensate outside the horizon. We use numerical solutions of the perturbed field equations and astrophysical models of massive and stellar-mass black hole populations to compute, for the first time, the stochastic gravitational-wave background from these sources. In optimistic scenarios the background is observable by Advanced LIGO and LISA for field masses ms in the range 3c[2
710-13,10-12] and 3c5
7[10-19,10-16] eV, respectively, and it can affect the detectability of resolvable sources. Our estimates suggest that an analysis of the stochastic background limits from LIGO O1 might already be used to marginally exclude axions with mass 3c10-12.5 eV. Semicoherent searches with Advanced LIGO (LISA) should detect 3c15(5) to 200(40) resolvable sources for scalar field masses 3
710-13 (10-17) eV. LISA measurements of massive BH spins could either rule out bosons in the range 3c[10-18,2
710-13] eV, or measure ms with 10% accuracy in the range 3c[10-17,10-13] eV
BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
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-CDM expectation of in the range
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 deg for an equivalent survey weight of 250,000
K. 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 .Comment: 13 pages, 9 figure
BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization
We present measurements of polarization lensing using the 150 GHz maps which
include all data taken by the BICEP2 & Keck Array CMB polarization experiments
up to and including the 2014 observing season (BK14). Despite their modest
angular resolution (), the excellent sensitivity (K-arcmin) of these maps makes it possible to directly reconstruct the
lensing potential using only information at larger angular scales (). From the auto-spectrum of the reconstructed potential we measure an
amplitude of the spectrum to be (Planck
CDM prediction corresponds to ), and reject
the no-lensing hypothesis at 5.8, which is the highest significance
achieved to date using an EB lensing estimator. Taking the cross-spectrum of
the reconstructed potential with the Planck 2015 lensing map yields
. These direct measurements of
are consistent with the CDM cosmology, and with
that derived from the previously reported BK14 B-mode auto-spectrum (). We perform a series of null tests and consistency
checks to show that these results are robust against systematics and are
insensitive to analysis choices. These results unambiguously demonstrate that
the B-modes previously reported by BICEP / Keck at intermediate angular scales
() are dominated by gravitational lensing. The
good agreement between the lensing amplitudes obtained from the lensing
reconstruction and B-mode spectrum starts to place constraints on any
alternative cosmological sources of B-modes at these angular scales.Comment: 12 pages, 8 figure
The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin
of our cosmic habitat. The age-old questions have been transformed into two
pressing issues primed for attack in the coming decade: How did the Universe
begin? and What physical laws govern the Universe at the highest energies? The
clearest window onto these questions is the pattern of polarization in the
Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial
gravity waves. A detection of the special pattern produced by gravity waves
would be not only an unprecedented discovery, but also a direct probe of
physics at the earliest observable instants of our Universe. Experiments which
map CMB polarization over the coming decade will lead us on our first steps
towards answering these age-old questions.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 212 author available at http://cmbpol.uchicago.ed
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