603 research outputs found
Self-interacting dark matter and Higgs bosons in the SU(3)_C x SU(3)_L x U(1)_N model with right-handed neutrinos
We investigate the possibility that dark matter could be made from CP-even
and CP- odd Higgs bosons in the SU(3)_C X SU(3)_L X U(1)_N (3-3-1) model with
right-handed neutrinos. This self-interacting dark matters are stable without
imposing of new symmetry and should be weak-interacting.Comment: 7 pages, Latex, To appear in Europhys. Let
Crinkles in the last scattering surface: Non-Gaussianity from inhomogeneous recombination
The perturbations in the electron number density during recombination
contributes to the Cosmic Microwave Background bispectrum through second order
terms. Perturbations in the electron density can be a factor of ~5 larger than
the baryon density fluctuations on large scales as shown in the calculations by
Novosyadlyj. This raises the possibility that the contribution to bispectrum
arising from perturbations in the optical depth may be non-negligible. We
calculate this bispectrum and find it to peak for squeezed triangles and of
peak amplitude of the order of primordial non-Gaussianity of local type with
fNL of 0.05 ~ -1 depending on the l-modes being considered. This is because the
shape of the bispectrum is different from the primordial one although it peaks
for squeezed configurations, similar to the local type primordial
non-Gaussianity.Comment: minor typos fixed, acknowledgement and reference adde
Halo detection via large-scale Bayesian inference
We present a proof-of-concept of a novel and fully Bayesian methodology
designed to detect halos of different masses in cosmological observations
subject to noise and systematic uncertainties. Our methodology combines the
previously published Bayesian large-scale structure inference algorithm, HADES,
and a Bayesian chain rule (the Blackwell-Rao Estimator), which we use to
connect the inferred density field to the properties of dark matter halos. To
demonstrate the capability of our approach we construct a realistic galaxy mock
catalogue emulating the wide-area 6-degree Field Galaxy Survey, which has a
median redshift of approximately 0.05. Application of HADES to the catalogue
provides us with accurately inferred three-dimensional density fields and
corresponding quantification of uncertainties inherent to any cosmological
observation. We then use a cosmological simulation to relate the amplitude of
the density field to the probability of detecting a halo with mass above a
specified threshold. With this information we can sum over the HADES density
field realisations to construct maps of detection probabilities and demonstrate
the validity of this approach within our mock scenario. We find that the
probability of successful of detection of halos in the mock catalogue increases
as a function of the signal-to-noise of the local galaxy observations. Our
proposed methodology can easily be extended to account for more complex
scientific questions and is a promising novel tool to analyse the cosmic
large-scale structure in observations.Comment: 17 pages, 13 figures. Accepted for publication in MNRAS following
moderate correction
Bayesian Power Spectrum Analysis of the First-Year WMAP data
We present the first results from a Bayesian analysis of the WMAP first year
data using a Gibbs sampling technique. Using two independent, parallel
supercomputer codes we analyze the WMAP Q, V and W bands. The analysis results
in a full probabilistic description of the information the WMAP data set
contains about the power spectrum and the all-sky map of the cosmic microwave
background anisotropies. We present the complete probability distributions for
each C_l including any non-Gaussianities of the power spectrum likelihood.
While we find good overall agreement with the previously published WMAP
spectrum, our analysis uncovers discrepancies in the power spectrum estimates
at low l multipoles. For example we claim the best-fit Lambda-CDM model is
consistent with the C_2 inferred from our combined Q+V+W analysis with a 10%
probability of an even larger theoretical C_2. Based on our exact analysis we
can therefore attribute the "low quadrupole issue" to a statistical
fluctuation.Comment: 5 pages. 4 figures. For additional information and data see
http://www.astro.uiuc.edu/~iodwyer/research#wma
Bayesian analysis of the low-resolution polarized 3-year WMAP sky maps
We apply a previously developed Gibbs sampling framework to the foreground
corrected 3-yr WMAP polarization data and compute the power spectrum and
residual foreground template amplitude posterior distributions. We first
analyze the co-added Q- and V-band data, and compare our results to the
likelihood code published by the WMAP team. We find good agreement, and thus
verify the numerics and data processing steps of both approaches. However, we
also analyze the Q- and V-bands separately, allowing for non-zero EB
cross-correlations and including two individual foreground template amplitudes
tracing synchrotron and dust emission. In these analyses, we find tentative
evidence of systematics: The foreground tracers correlate with each of the Q-
and V-band sky maps individually, although not with the co-added QV map; there
is a noticeable negative EB cross-correlation at l <~ 16 in the V-band map; and
finally, when relaxing the constraints on EB and BB, noticeable differences are
observed between the marginalized band powers in the Q- and V-bands. Further
studies of these features are imperative, given the importance of the low-l EE
spectrum on the optical depth of reionization tau and the spectral index of
scalar perturbations n_s.Comment: 5 pages, 4 figures, submitted to ApJ
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