The Planck satellite and cosmic concordance

In 2013, the Planck satellite, the third generation Cosmic Microwave Background (CMB) satellite following COBE and WMAP, took its last observations and was flung out from L2 orbit where it had been collecting data since 2009. The final release of data and papers from the Planck collaboration will take place this fall of 2017. Planck's high fidelity maps of the CMB temperature and polarization have taught us an enormous amount about our universe, and I will review some of what we have learned, with a focus on giving simple explanations of the way in which these observations have constrained and confirmed the ΛCDM model. Despite the good agreement with ΛCDM, much attention has been given to possible hints of new physics in the Planck data, and I will describe our endeavor to confirm or deny them using the computational resources from citizen scientists at Cosmology@Home. Part of these hints could be explained as an excess gravitational lensing distortion of the CMB beyond that expected. The gravitational lensing effect will be pristinely measured by future CMB experiments, and I will describe my recent work developing methods to optimally infer the gravitational lensing potential from CMB observations

Using CMB lensing to constrain the multiplicative bias of cosmic shear

Weak gravitational lensing is one of the key probes of cosmology. Cosmic shear surveys aimed at measuring the distribution of matter in the universe are currently being carried out (Pan-STARRS) or planned for the coming decade (DES, LSST, EUCLID, WFIRST). Crucial to the success of these surveys is the control of systematics. In this work a new method to constrain one such family of systematics, known as multiplicative bias, is proposed. This method exploits the cross-correlation between weak lensing measurements from galaxy surveys and the ones obtained from high resolution CMB experiments. This cross-correlation is shown to have the power to break the degeneracy between the normalization of the matter power spectrum and the multiplicative bias of cosmic shear and to be able to constrain the latter to a few percent.Comment: 5 pages, 1 figur

How Massless Neutrinos Affect the Cosmic Microwave Background Damping Tail

We explore the physical origin and robustness of constraints on the energy density in relativistic species prior to and during recombination, often expressed as constraints on an effective number of neutrino species, Neff. Constraints from current data combination of Wilkinson Microwave Anisotropy Probe (WMAP) and South Pole Telescope (SPT) are almost entirely due to the impact of the neutrinos on the expansion rate, and how those changes to the expansion rate alter the ratio of the photon diffusion scale to the sound horizon scale at recombination. We demonstrate that very little of the constraining power comes from the early Integrated Sachs-Wolfe (ISW) effect, and also provide a first determination of the amplitude of the early ISW effect. Varying the fraction of baryonic mass in Helium, Yp, also changes the ratio of damping to sound-horizon scales. We discuss the physical effects that prevent the resulting near-degeneracy between Neff and Yp from being a complete one. Examining light element abundance measurements, we see no significant evidence for evolution of Neff and the baryon-to-photon ratio from the epoch of big bang nucleosynthesis to decoupling. Finally, we consider measurements of the distance-redshift relation at low to intermediate redshifts and their implications for the value of Neff.Comment: 11 pages. Replaced version extends our discussion of origin of constraints and updates for current data, submitted to PR

Schottky Barriers on GaAs

The forward current of Schottky barriers on n-type GaAs is investigated as a function of electron concentration in the range of 8×10^17 to 8×10^18 cm^−3 at temperatures 297-4.2°K. Both vacuum-cleaved and chemically polished surfaces are used. The majority of the junctions studied are gold Schottky barriers, but tin and lead contacts are also examined. The predominant current mechanism is field emission at liquid-nitrogen temperature and below for the range of electron concentrations used. These data are in excellent quantitative agreement at 77°K with the field-emission analysis of Padovani and Stratton if one uses a two-band model for the imaginary wave number kn. At 297°K, thermionic field emission predominates, but for an electron density above 3×1018 cm−3 the field-emission mechanism with a two-band model still gives reasonable agreement