Session J8: Cosmic Microwave Background and Analysis Techniques

Primordial Non-Gaussianity (fNL) in WMAP data

We present evidence for the detection of primordial non- Gaussianity of the local type ($f_{NL}$), using the temperature information of the Cosmic Microwave Background (CMB) from the WMAP 3-year data. We employ the bispectrum estimator of non- Gaussianity described in Yadav et al. 2007 which allows us to analyze the entirety of the WMAP data without an arbitrary cut- off in angular scale. Using the combined information from WMAP's two main science channels up to $\ell_{max}=750$ and the conservative Kp0 foreground mask we find $26.9 < \mathbf {f_ {\rm NL}} < 146.7$ at $95 \%$ C.L., with a central value of $f_ {NL}=86.8$. This corresponds to a rejection of $f_{NL}=0$ at more than 99.5\% significance. We find that this detection is robust to variations in $l_{max}$, frequency and masks. We conclude that the WMAP 3-year data disfavors single field slow- roll inflation.   

Effects of a Primordial Magnetic Field on Low and High Multipoles of the CMB

The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies of the cosmic microwave background (CMB). It also provides a plausible explanation for the possible disparity between observations and theoretical fits to the CMB power spectrum. Here we report on numerical calculations of the CMB power spectrum and analyze the correlations between the CMB power spectrum from the PMF and the primary curvature perturbations. We deduce a precise estimate of the PMF effect on all modes of perturbations. We find that the PMF affects not only the CMB TT and TE modes on small angular scales, but also on large angular scales. The introduction of a PMF leads to a better fit to the CMB power spectrum for the higher multipoles, and the fit at lowest multipoles can be used to constrain the correlation of the PMF with density fluctuations for large negative values of the spectral index. Our prediction for the BB mode for a PMF average field strength of $|B_\lambda| =4.0 $ nG is consistent with the upper limit on the BB mode deduced from the latest CMB observations. We find that the BB mode is dominated by the vector mode of the PMF for higher multipoles. We also show that by fitting the complete power spectrum one can break the degeneracy between the PMF amplitude and its power spectral index.   

A search for Lorentz violation in the CMB.

Cosmic microwave background radiation provides an excellent opportunity for searches for vacuum birefringence. Rotation in the polarization of electromagnetic radiation is one consequence of birefringence and provides a signature for violations of Lorentz invariance. The extreme distances involved imply that tiny defects in propagation might accumulate to appreciable levels, yielding high sensitivities to possible Lorentz violations.   

Pico: Parameters for the Impatient Cosmologist

We present a fast, accurate and robust method of accelerating cosmological parameter estimation. The algorithm, called Pico, can compute the CMB power spectrum, matter transfer function and WMAP likelihood in about 20 milliseconds. This is approximately 1500 times faster than CAMB at default accuracies and 250,000 times faster at high accuracy. For the 9 parameter nonflat case presented here Pico can on average compute the TT, TE and EE spectra to better than 1\% of cosmic standard deviation for nearly all $\ell$ values over a large region of parameter space. By removing the major bottlenecks in parameter estimation codes, Pico decreases the computational time required to explore the parameter posterior by 1 or 2 orders of magnitude. Performing a cosmological parameter analysis of current CMB and large scale structure data, we show that these power spectra give very accurate 1 and 2 dimensional parameter posteriors. Training Pico can be done using massively parallel computing resources, including distributed computing projects such as Cosmology@Home.   

Bayesian Forecasting of Cosmological Parameter Constraints for Future Experiments.

In the era of precision cosmology, observational efforts are driven by expensive well planned missions. As we move towards more precise measurements, it is thus imperetive to estimate the constraints from the Proposed Observational Survey, more accurately. Here, we propose a method of forecasting cosmological parameter constraints from future surveys which go beyond the usual method of Fisher Analysis.   

Astronomical Data Analysis on Graphics Cards

Increasing detector sizes and advanced algorithms make astronomical data analysis tasks computationally demanding. Tools are therefore needed that simplify the development of parallel data analysis algorithms. Modern graphics cards offer a large amount of processing power at low cost and therefore have the potential to benefit these analyzes. However, the massively parallel nature of these devices makes them difficult to develop for. In this talk, we present a library of general purpose vector operations that can run on graphics cards. Bindings to widely used data analysis tools, including IDL and Matlab are provided, enabling scientists to take advantage of the enhanced processing power from within a familiar environment. We will present the programming interface and performance results for example applications.