511 research outputs found
SCoPE: An efficient method of Cosmological Parameter Estimation
Markov Chain Monte Carlo (MCMC) sampler is widely used for cosmological
parameter estimation from CMB and other data. However, due to the intrinsic
serial nature of the MCMC sampler, convergence is often very slow. Here we
present a fast and independently written Monte Carlo method for cosmological
parameter estimation named as Slick Cosmological Parameter Estimator (SCoPE),
that employs delayed rejection to increase the acceptance rate of a chain, and
pre-fetching that helps an individual chain to run on parallel CPUs. An
inter-chain covariance update is also incorporated to prevent clustering of the
chains allowing faster and better mixing of the chains. We use an adaptive
method for covariance calculation to calculate and update the covariance
automatically as the chains progress. Our analysis shows that the acceptance
probability of each step in SCoPE is more than and the convergence of
the chains are faster. Using SCoPE, we carry out some cosmological parameter
estimations with different cosmological models using WMAP-9 and Planck results.
One of the current research interests in cosmology is quantifying the nature of
dark energy. We analyze the cosmological parameters from two illustrative
commonly used parameterisations of dark energy models. We also asses primordial
helium fraction in the universe can be constrained by the present CMB data from
WMAP-9 and Planck. The results from our MCMC analysis on the one hand helps us
to understand the workability of the SCoPE better, on the other hand it
provides a completely independent estimation of cosmological parameters from
WMAP-9 and Planck data.Comment: 22 pages, 10 figures, 2 table
Suppressing CMB low multipoles with ISW effect
Recent results of Planck data reveal that the power in the low multipoles of
the CMB angular power spectrum, approximately up to , is significantly
lower than the theoretically predicted in the best fit CDM model. In
this paper we investigate the possibility of invoking the Integrated
Sachs-Wolfe (ISW) effect to explain this power deficit at low multipoles. The
ISW effect that originates from the late time expansion history of the universe
is rich in possibilities given the limited understanding of the origin of dark
energy (DE). It is a common understanding that the ISW effect adds to the power
at the low multipoles of the CMB angular power spectrum. In this paper we carry
out an analytic study to show that there are some expansion histories in which
the ISW effect, instead of adding power, provides negative contribution to the
power at low multipoles. Guided by the analytic study, we present examples of
the features required in the late time expansion history of the universe that
could explain the power deficiency through the ISW effect. We also show that an
ISW origin of power deficiency is consistent, at present, with other
cosmological observations that probe the expansion history such as distance
modulus, matter power spectrum and the evolution of cluster number count. We
also show that the ISW effect may be distinguished from power deficit
originating from features in the PPS using the measurements of the CMB
polarization spectrum at low multipoles expected from Planck. We conclude that
the power at low multipoles of the CMB anisotropy could well be closely linked
to Dark Energy puzzle in cosmology and this observation could be actually
pointing to richer phenomenology of DE beyond the cosmological constant
. (abbreviated)Comment: 20 pages, 7 figure
Revised cosmological parameters after BICEP 2 and BOSS
Estimation of parameters of the \lq standard\rq \,model of cosmology have
dramatically improved over past few decades due to increasingly exquisite
measurements made by Cosmic Microwave Background (CMB) experiments. Recent data
from Planck matches well with the minimal CDM model. A likelihood
analysis using Planck, WMAP and a selection of high resolution experiments
(highL), tensor to scalar ratio is found to be when
. Planck also imposes an upper bound on neutrino mass eV using Planck+WMAP+highL+BAO likelihood. However, recently
results from BICEP 2 claims the detection of from
polarization spectra. Further, results from SDSS-III BOSS large scale galaxy
survey constrains the total neutrino mass to eV. It
is important to study the consequences of these new measurements on other
cosmological parameters. In this paper we assess the revised constraints on
cosmological parameters in light of these two measurements that are in some
tension with the constraints from Planck. Using the prior on as
measured by SDSS-III BOSS and BICEP 2 likelihood, we find that the model with
running spectral index () leads to a value of at
. But, the model with makes consistent
with , at and also shows that is consistent with
its theoretical value of at around . Therefore, the analysis
in this paper shows that the model with gives consistency
with other cosmological parameters ( and ) when the current
limits on and are considered. However, on reducing the
value of , the model with non-zero gives consistent
result of [abridged].Comment: 14 pages, 10 figures. Matches the published versio
ISW effect as probe of features in the expansion history of the Universe
In this paper, using and implementing a new line of sight CMB code, called
CMBAns [1], that allows us to modify H(z) for any given feature at any redshift
we study the effect of changes in the expansion history of the Universe on the
CMB power spectrum. Motivated by the detailed analytical calculations of the
effects of the changes in H(z) on ISW plateau and CMB low multipoles, we study
two phenomenological parametric form of the expansion history using WMAP data
and through MCMC analysis. Our MCMC analysis shows that the standard LCDM
cosmological model is consistent with the CMB data allowing the expansion
history of the Universe vary around this model at different redshifts. However,
our analysis also shows that a decaying dark energy model proposed in [2] has
in fact a marginally better fit than the standard cosmological constant model
to CMB data. Concordance of our studies here with the previous analysis showing
that Baryon Acoustic Oscillation (BAO) and supernovae data (SN Ia) also prefer
mildly this decaying dark energy model to LCDM, makes this finding interesting
and worth further investigation.Comment: 20 pages, 11 figures, 2 tables, discussions extended, references
added, results unchanged, matches final version published in JCA
The Status and Impact of Technostress on Library Professionals: A Study among the Professionals of the Selected Private College Libraries in North Bengal
The article sought to examine the causes, symptoms and reducing strategies of technostress among the library professionals of the selected Private College Libraries in North Bengal. The descriptive survey method was employed using the questionnaire to collect data from the 52 respondents in ten higher education institutions in the northern region of West Bengal. The gathered data were analyzed by using the Likert scale and mean value calculation. The findings of the investigation show that library professionals experience technostress to a great extent. It was identified that the major cause of technostress was information overload. Different reducing strategies of technostress also revealed through this study
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