90 research outputs found
Objective Bayesian analysis of neutrino masses and hierarchy
Given the precision of current neutrino data, priors still impact noticeably
the constraints on neutrino masses and their hierarchy. To avoid our
understanding of neutrinos being driven by prior assumptions, we construct a
prior that is mathematically minimally informative. Using the constructed
uninformative prior, we find that the normal hierarchy is favoured but with
inconclusive posterior odds of 5.1:1. Better data is hence needed before the
neutrino masses and their hierarchy can be well constrained. We find that the
next decade of cosmological data should provide conclusive evidence if the
normal hierarchy with negligible minimum mass is correct, and if the
uncertainty in the sum of neutrino masses drops below 0.025 eV. On the other
hand, if neutrinos obey the inverted hierarchy, achieving strong evidence will
be difficult with the same uncertainties. Our uninformative prior was
constructed from principles of the Objective Bayesian approach. The prior is
called a reference prior and is minimally informative in the specific sense
that the information gain after collection of data is maximised. The prior is
computed for the combination of neutrino oscillation data and cosmological data
and still applies if the data improve.Comment: 15 pages. Minor changes to match accepted version in JCA
On the insufficiency of arbitrarily precise covariance matrices: non-Gaussian weak lensing likelihoods
We investigate whether a Gaussian likelihood, as routinely assumed in the
analysis of cosmological data, is supported by simulated survey data. We define
test statistics, based on a novel method that first destroys Gaussian
correlations in a dataset, and then measures the non-Gaussian correlations that
remain. This procedure flags pairs of datapoints which depend on each other in
a non-Gaussian fashion, and thereby identifies where the assumption of a
Gaussian likelihood breaks down. Using this diagnostic, we find that
non-Gaussian correlations in the CFHTLenS cosmic shear correlation functions
are significant. With a simple exclusion of the most contaminated datapoints,
the posterior for is shifted without broadening, but we find no
significant reduction in the tension with derived from Planck Cosmic
Microwave Background data. However, we also show that the one-point
distributions of the correlation statistics are noticeably skewed, such that
sound weak lensing data sets are intrinsically likely to lead to a
systematically low lensing amplitude being inferred. The detected
non-Gaussianities get larger with increasing angular scale such that for future
wide-angle surveys such as Euclid or LSST, with their very small statistical
errors, the large-scale modes are expected to be increasingly affected. The
shifts in posteriors may then not be negligible and we recommend that these
diagnostic tests be run as part of future analyses.Comment: Replacement to match accepted MNRAS versio
Recovering galaxy star formation and metallicity histories from spectra using VESPA
We introduce VErsatile SPectral Analysis (VESPA): a new method which aims to
recover robust star formation and metallicity histories from galactic spectra.
VESPA uses the full spectral range to construct a galaxy history from synthetic
models. We investigate the use of an adaptative parametrization grid to recover
reliable star formation histories on a galaxy-by-galaxy basis. Our goal is
robustness as opposed to high resolution histories, and the method is designed
to return high time resolution only where the data demand it. In this paper we
detail the method and we present our findings when we apply VESPA to synthetic
and real Sloan Digital Sky Survey (SDSS) spectroscopic data. We show that the
number of parameters that can be recovered from a spectrum depends strongly on
the signal-to-noise, wavelength coverage and presence or absence of a young
population. For a typical SDSS sample of galaxies, we can normally recover
between 2 to 5 stellar populations. We find very good agreement between VESPA
and our previous analysis of the SDSS sample with MOPED.Comment: In press MNRAS, minor revisions to match accepted version by the
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