2,151 research outputs found
Multiple inflation and the WMAP 'glitches' II. Data analysis and cosmological parameter extraction
Detailed analyses of the WMAP data indicate possible oscillatory features in
the primordial curvature perturbation, which moreover appears to be suppressed
beyond the present Hubble radius. Such deviations from the usual inflationary
expectation of an approximately Harrison-Zeldovich spectrum are expected in the
supergravity-based 'multiple inflation' model wherein phase transitions during
inflation induce sudden changes in the mass of the inflaton, thus interrupting
its slow-roll. In a previous paper we calculated the resulting curvature
perturbation and showed how the oscillations arise. Here we perform a Markov
Chain Monte Carlo fitting exercise using the 3-year WMAP data to determine how
the fitted cosmological parameters vary when such a primordial spectrum is used
as an input, rather than the usually assumed power-law spectrum. The
'concordance' LCDM model is still a good fit when there is just a 'step' in the
spectrum. However if there is a 'bump' in the spectrum (due e.g. to two phase
transitions in rapid succession), the precision CMB data can be well-fitted by
a flat Einstein-de Sitter cosmology without dark energy. This however requires
the Hubble constant to be h ~ 0.44 which is lower than the locally measured
value. To fit the SDSS data on the power spectrum of galaxy clustering requires
a ~10% component of hot dark matter, as would naturally be provided by 3
species of neutrinos of mass ~0.5 eV. This CHDM model cannot however fit the
position of the baryon acoustic peak in the LRG redshift two-point correlation
function. It may be possible to overcome these difficulties in an inhomogeneous
Lemaitre-Tolman-Bondi cosmological model with a local void, which can
potentially also account for the SN Ia Hubble diagram without invoking cosmic
acceleration.Comment: 27 pages, 18 figures (RevTex); Tables revised to include the \chi^2
and "Akaike information criterion" in comparison of cosmological models; Fits
to WMAP3 EE spectrum shown; Additional references added; Accepted for
publication in in Phys Rev
Search for features in the spectrum of primordial perturbations using Planck and other datasets
We reconstruct the power spectrum of primordial curvature perturbations by applying a well-validated non-parametric technique employing Tikhonov regularisation to the first data release from the Planck satellite. To improve the reconstruction on small spatial scales we include data from the ground-based ACT and SPT experiments, the WiggleZ galaxy redshift survey, the CFHTLenS tomographic weak lensing survey, and spectral analysis of the Lyman-Îą forest. The reconstructed scalar spectrum (assuming the standard ÎCDM cosmology) is not scale-free but has an infrared cutoff at k Ⲡ5 Ă 10-4 Mpc-1 and several (2-3)Ď features, of which two at wavenumber k/Mpc-1 0.0018 and 0.057 had been seen already in WMAP data. A higher significance feature at k âź 0.12 Mpc-1 is indicated by Planck data, but may be sensitive to the systematic uncertainty around multipole â âź 1800 in the 217Ă217 GHz cross-spectrum. In any case accounting for the 'look elsewhere' effect decreases its global significance to âź2Ď
Synthesis and Characterization of MnO2 as Electrocatalytic Energy Material for Fuel Cell Electrode
Development Inexpensive non Pt based high electrocatalytic energy materials is the need of hour for fuel cell electrode to produce clean alternative green energy from synthesized Bio alcohol from Biomass. MnO2 electro synthesized at different current density is found to be well performed electrocatalytic material, comparable to Pt, with higher current density, very low over voltage for electrochemical oxidation of methanol . From EIS study, the polarization resistance of the coated MnO2 is found to be much low and electrical double layer capacitance is high, the effect increases with increase in current density of electro deposition. XRD , EDX and AAS analysis confirm the MnO2 deposition, the amount increases with current density. SEM morphology exhibits enhanced 3D effective substrate area for electro oxidation of the fuel and a few nano structured grains of deposited MnO2 at higher current density. The fact supports an improved electro catalytic property to be applied as high energetic materials for fuel cell Electrode. Keywords: Electro catalytic ; Energy Material; Fuel Cell: Impedance; Polarization; Electro coatin
Using cosmic neutrinos to search for non-perturbative physics at the Pierre Auger Observatory
The Pierre Auger (cosmic ray) Observatory provides a laboratory for studying
fundamental physics at energies far beyond those available at colliders. The
Observatory is sensitive not only to hadrons and photons, but can in principle
detect ultrahigh energy neutrinos in the cosmic radiation. Interestingly, it
may be possible to uncover new physics by analyzing characteristics of the
neutrino flux at the Earth. By comparing the rate for quasi-horizontal, deeply
penetrating air showers triggered by all types of neutrinos, with the rate for
slightly upgoing showers generated by Earth-skimming tau neutrinos, we
determine the ratio of events which would need to be detected in order to
signal the existence of new non-perturbative interactions beyond the TeV-scale
in which the final state energy is dominated by the hadronic component. We use
detailed Monte Carlo simulations to calculate the effects of interactions in
the Earth and in the atmosphere. We find that observation of 1 Earth-skimming
and 10 quasi-horizontal events would exclude the standard model at the 99%
confidence level. If new non-perturbative physics exists, a decade or so would
be required to find it in the most optimistic case of a neutrino flux at the
Waxman-Bahcall level and a neutrino-nucleon cross-section an order of magnitude
above the standard model prediction.Comment: 8 pages revtex, 4 eps figure
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