142 research outputs found
The cut-sky cosmic microwave background is not anomalous
The observed angular correlation function of the cosmic microwave background
has previously been reported to be anomalous, particularly when measured in
regions of the sky uncontaminated by Galactic emission. Recent work by
Efstathiou et al. presents a Bayesian comparison of isotropic theories, casting
doubt on the significance of the purported anomaly. We extend this analysis to
all anisotropic Gaussian theories with vanishing mean ( = 0), using
the much wider class of models to confirm that the anomaly is not likely to
point to new physics. On the other hand if there is any new physics to be
gleaned, it results from low-l alignments which will be better quantified by a
full-sky statistic.
We also consider quadratic maximum likelihood power spectrum estimators that
are constructed assuming isotropy. The underlying assumptions are therefore
false if the ensemble is anisotropic. Nonetheless we demonstrate that, for
theories compatible with the observed sky, these estimators (while no longer
optimal) remain statistically superior to pseudo-C_l power spectrum estimators.Comment: PRD in press. Extremely minor updates, mirroring typographical
changes made in proo
No new cosmological concordance with massive sterile neutrinos
It has been claimed recently that massive sterile neutrinos could bring about
a new concordance between observations of the cosmic microwave background
(CMB), the large-scale structure (LSS) of the Universe, and local measurements
of the Hubble constant, . We demonstrate that this apparent concordance
results from combining datasets which are in significant tension, even within
this extended model, possibly indicating remaining systematic biases in the
measurements. We further show that this tension remains when the cosmological
model is further extended to include significant tensor modes, as suggested by
the recent BICEP2 results. Using the Bayesian evidence, we show that the
minimal CDM model is strongly favoured over its neutrino extensions by
various combinations of datasets. Robust data combinations yield stringent
limits of eV and eV at CL for the sum of active and sterile neutrinos,
respectively.Comment: 6 pages, version accepted by PR
Accretion of a Symmetry Breaking Scalar Field by a Schwarzschild Black Hole
We simulate the behaviour of a Higgs-like field in the vicinity of a
Schwarzschild black hole using a highly accurate numerical framework. We
consider both the limit of the zero-temperature Higgs potential, and a toy
model for the time-dependent evolution of the potential when immersed in a
slowly cooling radiation bath. Through these numerical investigations, we aim
to improve our understanding of the non-equilibrium dynamics of a symmetry
breaking field (such as the Higgs) in the vicinity of a compact object such as
a black hole. Understanding this dynamics may suggest new approaches for
studying properties of scalar fields using black holes as a laboratory.Comment: 16 pages, 5 figure
Is there evidence for additional neutrino species from cosmology?
It has been suggested that recent cosmological and flavor-oscillation data
favor the existence of additional neutrino species beyond the three predicted
by the Standard Model of particle physics. We apply Bayesian model selection to
determine whether there is indeed any evidence from current cosmological
datasets for the standard cosmological model to be extended to include
additional neutrino flavors. The datasets employed include cosmic microwave
background temperature, polarization and lensing power spectra, and
measurements of the baryon acoustic oscillation scale and the Hubble constant.
We also consider other extensions to the standard neutrino model, such as
massive neutrinos, and possible degeneracies with other cosmological
parameters. The Bayesian evidence indicates that current cosmological data do
not require any non-standard neutrino properties.Comment: 17 pages, 7 figures. v3: replaced with version published in JCAP
(typo fixes, including Figure 1 units
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