1,580 research outputs found
Finslerian dipolar modulation of the CMB power spectra at scales
A common explanation for the CMB power asymmetry is to introduce a dipolar
modulation at the stage of inflation, where the primordial power spectrum is
spatially varying. If the universe in the stage of inflation is Finslerian, and
if the Finsler spacetime is non-reversible under parity flip, ,
then a three dimensional spectrum which is the function of wave vector and
direction is valid. In this paper, a three dimensional primordial power
spectrum with preferred direction is derived in the framework of Finsler
spacetime. It is found that the amplitude of dipolar modulation is related to
the Finslerian parameter, which in turn is a function of wave vector. The
angular correlation coefficients are presented, and the numerical results for
the anisotropic correlation coefficients over the multipole range are
given.Comment: 13 pages, 1 figure, accepted by EPJ
Two-Photon-Exchange Effects and Deformation
The two-photon-exchange (TPE) contribution in with
and small is calculated and its corrections to the ratios
of electromagnetic transition form factors and ,
are analysed. A simple hadronic model is used to estimate the TPE amplitude.
Two phenomenological models, MAID2007 and SAID, are used to approximate the
full cross sections which contain both the TPE and the
one-photon-exchange (OPE) contributions. The genuine the OPE amplitude is then
extracted from an integral equation by iteration. We find that the TPE
contribution is not sensitive to whether MAID or SAID is used as input in the
region with GeV.
It gives small correction to while for , the correction is
about -10\% at small and about at large for
GeV. The large correction from TPE at small must
be included in the analysis to get a reliable extraction of .Comment: Talk given at Conference:C16-07-2
Multiple Testing for Neuroimaging via Hidden Markov Random Field
Traditional voxel-level multiple testing procedures in neuroimaging, mostly
-value based, often ignore the spatial correlations among neighboring voxels
and thus suffer from substantial loss of power. We extend the
local-significance-index based procedure originally developed for the hidden
Markov chain models, which aims to minimize the false nondiscovery rate subject
to a constraint on the false discovery rate, to three-dimensional neuroimaging
data using a hidden Markov random field model. A generalized
expectation-maximization algorithm for maximizing the penalized likelihood is
proposed for estimating the model parameters. Extensive simulations show that
the proposed approach is more powerful than conventional false discovery rate
procedures. We apply the method to the comparison between mild cognitive
impairment, a disease status with increased risk of developing Alzheimer's or
another dementia, and normal controls in the FDG-PET imaging study of the
Alzheimer's Disease Neuroimaging Initiative.Comment: A MATLAB package implementing the proposed FDR procedure is available
with this paper at the Biometrics website on Wiley Online Librar
Testing the homogeneity of the Universe using gamma-ray bursts
In this paper, we study the homogeneity of the GRB distribution using a
subsample of the Greiner GRB catalogue, which contains 314 objects with
redshift (244 of them discovered by the Swift GRB Mission). We try to
reconcile the dilemma between the new observations and the current theory of
structure formation and growth. To test the results against the possible biases
in redshift determination and the incompleteness of the Greiner sample, we also
apply our analysis to the 244 GRBs discovered by Swift and the subsample
presented by the Swift Gamma-Ray Burst Host Galaxy Legacy Survey (SHOALS). The
real space two-point correlation function (2PCF) of GRBs, is
calculated using a Landy-Szalay estimator. We perform a standard least-
fit to the measured 2PCFs of GRBs. We use the best-fit 2PCF to deduce a
recently defined homogeneity scale. The homogeneity scale, , is defined as
the comoving radius of the sphere inside which the number of GRBs is
proportional to within , or equivalently above which the correlation
dimension of the sample is within of . For the Swift
subsample of 244 GRBs, the correlation length and slope are Mpc and (at confidence level).
The corresponding scale for a homogeneous distribution of GRBs is Mpc. The results help to alleviate the tension between the new
discovery of the excess clustering of GRBs and the cosmological principle of
large-scale homogeneity. It implies that very massive structures in the
relatively local Universe do not necessarily violate the cosmological principle
and could conceivably be present.Comment: 7 pages, 5 figures, accepted by Astronomy & Astrophysics. The data
used in this work (e.g. Tables 1 and 2) are publicly available online in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A
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