Amit P. S. Yadav

Evidence of Primordial Non-Gaussianity (f(NL)) in the Wilkinson Microwave Anisotropy Probe 3-Year Data at 2.8sigma

We present evidence for the detection of primordial non-Gaussianity of the local type (fNL), 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 [1] 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 lmax = 750 and the conservative Kp0 foreground mask we find 27 < fNL < 147 at 95% C.L., with a central value of fNL = 87. This corresponds to a rejection of fNL = 0 at more than 99.5% significance. We find that this detection is robust to variations in lmax, frequency and masks, and that no known foreground, instrument systematic, or secondary anisotropy explains our signal while passing our suite of tests. We explore the impact of several analysis choices on the stated significance and find 2.5 σ for the most conservative view. We conclude that the WMAP 3-year data disfavors canonical single field slow-roll inflation.

Fast Estimator of Primordial Non-Gaussianity from Temperature and Polarization Anisotropies in the Cosmic Microwave Background

Measurements of primordial non-Gaussianity (fNL) open a new window onto the physics of inflation. We describe a fast cubic (bispectrum) estimator of fNL, using a combined analysis of temperature and polarization observations. The speed of our estimator allows us to use a sufficient number of Monte Carlo simulations to characterize its statistical properties in the presence of real-world issues such as instrumental effects, partial sky coverage, and foreground contamination. We find that our estimator is optimal, where optimality is defined by saturation of the Cramer-Rao bound, if noise is homogeneous. Our estimator is also computationally efficient, scaling as O(N3/2), compared to the O(N5/2) scaling of the brute-force bispectrum calculation for sky maps with N pixels. For Planck this translates into a speedup by factors of millions, reducing the required computing time from thousands of years to just hours and thus making fNL estimation feasible for future surveys.

Primordial Non-Gaussianity in the Cosmic Microwave Background

In the last few decades, advances in observational cosmology have given us a standard model of cosmology. We know the content of the universe to within a few percent. With more ambitious experiments on the way, we hope to move beyond the knowledge of what the universe is made of, to why the universe is the way it is. In this paper we focus on primordial non-Gaussianity as a probe of the physics of the dynamics of the universe at the very earliest moments. We discuss (1) theoretical predictions from inflationary models and their observational consequences in the cosmic microwave background (CMB) anisotropies; (2) CMB-based estimators for constraining primordial non-Gaussianity with an emphasis on bispectrum templates (3) current constraints on non-Gaussianity and what we can hope to achieve in the near future and (4) nonprimordial sources of non-Gaussianities in the CMB such as bispectrum due to second order effects, three way crosscorrelation between primary-lensing-secondary CMB, and possible instrumental effects.

Fast Estimator of Primordial Non-Gaussianity from Temperature and Polarization Anisotropies in the Cosmic Microwave Background II: Partial Sky Coverage and Inhomogeneous Noise

In the recent paper by Yadav and coworkers we described a fast cubic (bispectrum) estimator of the amplitude of primordial non-Gaussianity of local type, fNL, from a combined analysis of the cosmic microwave background (CMB) temperature and E-polarization observations. In this paper we generalize the estimator to deal with a partial sky coverage as well as inhomogeneous noise. Our generalized estimator is still computationally efficient, scaling as O(Npix3/2) compared to the O(Npix5/2) scaling of the brute-force bispectrum calculation for sky maps with Npix pixels. Upcoming CMB experiments are expected to yield high-sensitivity temperature and E-polarization data. Our generalized estimator will allow us to optimally utilize the combined CMB temperature and E-polarization information from these realistic experiments and to constrain primordial non-Gaussianity.

CMBPol Mission Concept Study: Probing Inflation with CMB Polarization

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of ination. We focus on the prospects for using CMB measurementsWe summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B‐mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super‐Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale‐dependence and non‐Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.

Probing inflation with CMB polarization

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of ination. We focus on the prospects for using CMB measurementsWe summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B‐mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super‐Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale‐dependence and non‐Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.

The Simons Array: expanding POLARBEAR to three multi-chroic telescopes

The Simons Array is an expansion of the POLARBEAR cosmic microwave background (CMB) polarization experiment currently observing from the Atacama Desert in Northern Chile. This expansion will create an array of three 3.5m telescopes each coupled to a multichroic bolometric receiver. The Simons Array will have the sensitivity to produce a ≥ 5σ detection of inationary gravitational waves with a tensor-to-scalar ratio r ≥ 0:01, detect the known minimum 58 meV sum of the neutrino masses with 3σ confidence when combined with a next-generation baryon acoustic oscillation measurement, and make a lensing map of large-scale structure over the 80% of the sky available from its Chilean site. These goals require high sensitivity and the ability to extract the CMB signal from contaminating astrophysical foregrounds; these requirements are met by coupling the three high-throughput telescopes to novel multichroic lenslet-coupled pixels each measuring CMB photons in both linear polarization states over multiple spectral bands. We present the status of this instrument already under construction, and an analysis of its capabilities.

Primordial magnetism in the CMB: Exact treatment of Faraday rotation and WMAP7 bounds

Faraday rotation induced B modes can provide a distinctive signature of primordial magnetic fields because of their characteristic frequency dependence and because they are only weakly damped on small scales, allowing them to dominate B modes from other sources. By numerically solving the full cosmic microwave background radiative transport equations, we study the B-mode power spectrum induced by stochastic magnetic fields that have significant power on scales smaller than the thickness of the last scattering surface. Constraints on the magnetic field energy density and inertial scale are derived from WMAP 7-year data, and are stronger than the big bang nucleosynthesis bound for a range of parameters. Observations of the cosmic microwave background polarization at smaller angular scales are crucial to provide tighter constraints or a detection.

Probing primordial magnetism with off-diagonal correlators of CMB polarization

Primordial magnetic fields (PMF) can create polarization

CMB tomography: Reconstruction of adiabatic primordial scalar potential using temperature and polarization maps

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