1,190 research outputs found
Bayesian model comparison applied to the Explorer-Nautilus 2001 coincidence data
Bayesian reasoning is applied to the data by the ROG Collaboration, in which
gravitational wave (g.w.) signals are searched for in a coincidence experiment
between Explorer and Nautilus. The use of Bayesian reasoning allows, under well
defined hypotheses, even tiny pieces of evidence in favor of each model to be
extracted from the data. The combination of the data of several experiments can
therefore be performed in an optimal and efficient way. Some models for
Galactic sources are considered and, within each model, the experimental result
is summarized with the likelihood rescaled to the insensitivity limit value
(`` function''). The model comparison result is given in in terms of
Bayes factors, which quantify how the ratio of beliefs about two alternative
models are modified by the experimental observationComment: 16 pages, 4 figures. Presented at the GWDAW2002 conference, held in
Kyoto on Dec.,2002. This version includes comments by the referees of CQG,
which has accepted the paper for pubblication in the special issue of the
conference. In particular, note that in Eq. 12 there was a typeset error. As
suggested by one of the referees, a uniform prior in Log(alpha) has also been
considere
The history of mass assembly of faint red galaxies in 28 galaxy clusters since z=1.3
We measure the relative evolution of the number of bright and faint (as faint
as 0.05 L*) red galaxies in a sample of 28 clusters, of which 16 are at 0.50<=
z<=1.27, all observed through a pair of filters bracketing the 4000 Angstrom
break rest-frame. The abundance of red galaxies, relative to bright ones, is
constant over all the studied redshift range, 0<z<1.3, and rules out a
differential evolution between bright and faint red galaxies as large as
claimed in some past works. Faint red galaxies are largely assembled and in
place at z=1.3 and their deficit does not depend on cluster mass, parametrized
by velocity dispersion or X-ray luminosity. Our analysis, with respect to
previous one, samples a wider redshift range, minimizes systematics and put a
more attention to statistical issues, keeping at the same time a large number
of clusters.Comment: MNRAS, 386, 1045. Half a single sentence (in sec 4.4) change
Bayesian Inference in Processing Experimental Data: Principles and Basic Applications
This report introduces general ideas and some basic methods of the Bayesian
probability theory applied to physics measurements. Our aim is to make the
reader familiar, through examples rather than rigorous formalism, with concepts
such as: model comparison (including the automatic Ockham's Razor filter
provided by the Bayesian approach); parametric inference; quantification of the
uncertainty about the value of physical quantities, also taking into account
systematic effects; role of marginalization; posterior characterization;
predictive distributions; hierarchical modelling and hyperparameters; Gaussian
approximation of the posterior and recovery of conventional methods, especially
maximum likelihood and chi-square fits under well defined conditions; conjugate
priors, transformation invariance and maximum entropy motivated priors; Monte
Carlo estimates of expectation, including a short introduction to Markov Chain
Monte Carlo methods.Comment: 40 pages, 2 figures, invited paper for Reports on Progress in Physic
Neural Network Parametrization of Deep-Inelastic Structure Functions
We construct a parametrization of deep-inelastic structure functions which
retains information on experimental errors and correlations, and which does not
introduce any theoretical bias while interpolating between existing data
points. We generate a Monte Carlo sample of pseudo-data configurations and we
train an ensemble of neural networks on them. This effectively provides us with
a probability measure in the space of structure functions, within the whole
kinematic region where data are available. This measure can then be used to
determine the value of the structure function, its error, point-to-point
correlations and generally the value and uncertainty of any function of the
structure function itself. We apply this technique to the determination of the
structure function F_2 of the proton and deuteron, and a precision
determination of the isotriplet combination F_2[p-d]. We discuss in detail
these results, check their stability and accuracy, and make them available in
various formats for applications.Comment: Latex, 43 pages, 22 figures. (v2) Final version, published in JHEP;
Sect.5.2 and Fig.9 improved, a few typos corrected and other minor
improvements. (v3) Some inconsequential typos in Tab.1 and Tab 5 corrected.
Neural parametrization available at http://sophia.ecm.ub.es/f2neura
The Bjorken sum rule with Monte Carlo and Neural Network techniques
Determinations of structure functions and parton distribution functions have
been recently obtained using Monte Carlo methods and neural networks as
universal, unbiased interpolants for the unknown functional dependence. In this
work the same methods are applied to obtain a parametrization of polarized Deep
Inelastic Scattering (DIS) structure functions. The Monte Carlo approach
provides a bias--free determination of the probability measure in the space of
structure functions, while retaining all the information on experimental errors
and correlations. In particular the error on the data is propagated into an
error on the structure functions that has a clear statistical meaning. We
present the application of this method to the parametrization from polarized
DIS data of the photon asymmetries and from which we determine
the structure functions and , and discuss the
possibility to extract physical parameters from these parametrizations. This
work can be used as a starting point for the determination of polarized parton
distributions.Comment: 24 pages, 6 figure
Can Old Galaxies at High Redshifts and Baryon Acoustic Oscillations Constrain H_0?
A new age-redshift test is proposed in order to constrain with basis on
the existence of old high redshift galaxies (OHRG). As should be expected, the
estimates of based on the OHRG are heavily dependent on the cosmological
description. In the flat concordance model (CDM), for example, the
value of depends on the mass density parameter . Such a degeneracy can be broken trough a joint analysis
involving the OHRG and baryon acoustic oscillation (BAO) signature. In the
framework of the model our joint analysis yields a value of
H_0=71^{+4}_{-4}\kms Mpc () with the best fit density
parameter . Such results are in good agreement with
independent studies from the {\it{Hubble Space Telescope}} key project and the
recent estimates of WMAP, thereby suggesting that the combination of these two
independent phenomena provides an interesting method to constrain the Hubble
constant.Comment: 16 pages, 6 figures, 1 tabl
Effects of age and gender on neural correlates of emotion imagery
Mental imagery is part of people's own internal processing and plays an important role in everyday life, cognition and pathology. The neural network supporting mental imagery is bottom-up modulated by the imagery content. Here, we examined the complex associations of gender and age with the neural mechanisms underlying emotion imagery. We assessed the brain circuits involved in emotion mental imagery (vs. action imagery), controlled by a letter detection task on the same stimuli, chosen to ensure attention to the stimuli and to discourage imagery, in 91 men and women aged 14–65 years using fMRI. In women, compared with men, emotion imagery significantly increased activation within the right putamen, which is involved in emotional processing. Increasing age, significantly decreased mental imagery-related activation in the left insula and cingulate cortex, areas involved in awareness of ones' internal states, and it significantly decreased emotion verbs-related activation in the left putamen, which is part of the limbic system. This finding suggests a top-down mechanism by which gender and age, in interaction with bottom-up effect of type of stimulus, or directly, can modulate the brain mechanisms underlying mental imagery
Statistical coverage for supersymmetric parameter estimation: a case study with direct detection of dark matter
Models of weak-scale supersymmetry offer viable dark matter (DM) candidates.
Their parameter spaces are however rather large and complex, such that pinning
down the actual parameter values from experimental data can depend strongly on
the employed statistical framework and scanning algorithm. In frequentist
parameter estimation, a central requirement for properly constructed confidence
intervals is that they cover true parameter values, preferably at exactly the
stated confidence level when experiments are repeated infinitely many times.
Since most widely-used scanning techniques are optimised for Bayesian
statistics, one needs to assess their abilities in providing correct confidence
intervals in terms of the statistical coverage. Here we investigate this for
the Constrained Minimal Supersymmetric Standard Model (CMSSM) when only
constrained by data from direct searches for dark matter. We construct
confidence intervals from one-dimensional profile likelihoods and study the
coverage by generating several pseudo-experiments for a few benchmark sets of
pseudo-true parameters. We use nested sampling to scan the parameter space and
evaluate the coverage for the benchmarks when either flat or logarithmic priors
are imposed on gaugino and scalar mass parameters. The sampling algorithm has
been used in the configuration usually adopted for exploration of the Bayesian
posterior. We observe both under- and over-coverage, which in some cases vary
quite dramatically when benchmarks or priors are modified. We show how most of
the variation can be explained as the impact of explicit priors as well as
sampling effects, where the latter are indirectly imposed by physicality
conditions. For comparison, we also evaluate the coverage for Bayesian credible
intervals, and observe significant under-coverage in those cases.Comment: 30 pages, 5 figures; v2 includes major updates in response to
referee's comments; extra scans and tables added, discussion expanded, typos
corrected; matches published versio
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