J. Dunkley

Initial conditions of the universe: How much isocurvature is allowed?

We investigate the constraints imposed by current data on correlated mixtures of adiabatic and nonadiabatic primordial perturbations. We discover subtle flat directions in parameter space that tolerate large (approximately 60%) fractions of nonadiabatic fluctuations. In particular, larger values of the baryon density and a spectral tilt are allowed. The cancellations in the degenerate directions are explored and the role of priors is elucidated.

Constraining thermal dust emission in distant galaxies with number counts and angular power spectra

We perform a joint fit to differential number counts from Spitzers MIPS and Herschels SPIRE instruments, and angular power spectra of cosmic infrared background (CIB) anisotropies from SPIRE, Planck, the Atacama Cosmology Telescope, and the South Pole Telescope, which together span 220 < \nu / GHz < 4300 (70 < \lambda / \mu m < 1400). We simultaneously constrain the dust luminosity function, thermal dust spectral energy distribution (SED) and clustering properties of CIB sources, and the evolution of these quantities over cosmic time. We find that the data strongly require redshift evolution in the thermal dust SED. In our adopted parametrization, this evolution takes the form of an increase in graybody dust temperature at high redshift, but it may also be related to a temperature - dust luminosity correlation or evolution in dust opacity. The counts and spectra together constrain the evolution of the thermal dust luminosity function up to z ~ 2.5-3, complementing approaches relying on rest-frame mid-infrared observations of the rarest bright objects. We are able to fit the power spectra without requiring a complex halo model approach, and show that neglecting scale-dependent halo bias may be impairing analyses that do use this framework.

Measuring the geometry of the universe in the presence of isocurvature modes.

The cosmic microwave background (CMB) anisotropy constrains the geometry of the Universe because the positions of the acoustic peaks of the angular power spectrum depend strongly on the curvature of three-dimensional space. In this Letter we exploit current observations to determine the geometry in the presence of isocurvature modes. Most previous analyses assumed that the primordial perturbations were adiabatic. A priori one might expect that allowing isocurvature modes would substantially degrade constraints on the curvature. We find, however, that with additional data sets, the geometry remains well constrained. When the most general isocurvature perturbation is allowed, the CMB alone can only poorly constrain the geometry to . Including large-scale structure data, one obtains Ohm(0) = 1.07 +/- 0.03, and 1.06 +/- 0.02 when supplemented by supernova data and the determination of H(0).

Future CMB tests of dark matter: Ultralight axions and massive neutrinos

Measurements of cosmic microwave background (CMB) anisotropies provide strong evidence for the existence of dark matter and dark energy. They can also test its composition, probing the energy density and particle mass of different dark-matter and dark-energy components. CMB data have already shown that ultralight axions (ULAs) with mass in the range 10 − 32     eV → 10 − 26     eV compose a fraction ≲ 0.01 of the cosmological critical density. The next Stage-IV CMB experiment (CMB-S4) (assuming a 1 arcmin beam and ∼ 1     μ K − arcmin noise levels over a sky fraction of 0.4) to the density of ULAs and other dark-sector components is assessed. CMB-S4 data should be ∼ 10 times more sensitive to the ULA energy density than Planck data alone, across a wide range of ULA masses 10 − 32 ≲ m a ≲ 10 − 23     eV , and will probe axion decay constants of f a ≈ 1 0 16     GeV , at the grand unified scale. CMB-S4 could improve the CMB lower bound on the ULA mass from ∼ 10 − 25     eV to 10 − 23     eV , nearing the mass range probed by dwarf galaxy abundances and dark-matter halo density profiles. These improvements will allow for a multi- σ detection of percent-level departures from CDM over a wide range of masses. Much of this improvement is driven by the effects of weak gravitational lensing on the CMB, which breaks degeneracies between ULAs and neutrinos. We also find that the addition of ULA parameters does not significantly degrade the sensitivity of the CMB to neutrino masses. These results were obtained using the axionCAMB code (a modification to the CAMB Boltzmann code), presented here for public use.

Complementing the ground-based CMB-S4 experiment on large scales with the PIXIE satellite

We present forecasts for cosmological parameters from future cosmic microwave background (CMB) data measured by the stage-4 (S4) generation of ground-based experiments in combination with large-scale anisotropy data from the PIXIE satellite. We demonstrate the complementarity of the two experiments and focus on science targets that benefit from their combination. We show that a cosmic-variance-limited measurement of the optical depth to reionization provided by PIXIE, with error σ(τ)=0.002, is vital for enabling a 5σ detection of the sum of the neutrino masses when combined with a CMB-S4 lensing measurement and with lower-redshift constraints on the growth of structure and the distance-redshift relation. Parameters characterizing the epoch of reionization will also be tightly constrained; PIXIE’s τ constraint converts into σ(zre)=0.2 for the mean time of reionization, and a kinematic Sunyaev-Zel’dovich measurement from S4 gives σ(Δzre)=0.03 for the duration of reionization. Both PIXIE and S4 will put strong constraints on primordial tensor fluctuations, vital for testing early-Universe models, and will do so at distinct angular scales. We forecast σ(r)≈5×10−4 for a signal with a tensor-to-scalar ratio r=10−3, after accounting for diffuse foreground removal and delensing. The wide and dense frequency coverage of PIXIE results in an expected foreground-degradation factor on r of only ≈25%. By measuring large and small scales PIXIE and S4 will together better limit the energy injection at recombination from dark matter annihilation, with pann<0.09×10−6  m3/s/kg projected at 95% confidence. Cosmological parameters measured from the damping tail with S4 will be best constrained by polarization, which has the advantage of minimal contamination from extragalactic emission.

The Python Sky Model: software for simulating the Galactic microwave sky

We present a numerical code to simulate maps of Galactic emission in intensity and polarization at microwave frequencies, aiding in the design of cosmic microwave background experiments. This python code builds on existing efforts to simulate the sky by providing an easy-to-use interface and is based on publicly available data from the WMAP (Wilkinson Microwave Anisotropy Probe) and Planck satellite missions. We simulate synchrotron, thermal dust, free–free and anomalous microwave emission over the whole sky, in addition to the cosmic microwave background, and include a set of alternative prescriptions for the frequency dependence of each component, for example, polarized dust with multiple temperatures and a decorrelation of the signals with frequency, which introduce complexity that is consistent with current data. We also present a new prescription for adding small-scale realizations of these components at resolutions greater than current all-sky measurements. The usefulness of the code is demonstrated by forecasting the impact of varying foreground complexity on the recovered tensor-to-scalar ratio for the LiteBIRD satellite. The code is available at: https://github.com/bthorne93/PySM_public.

Survey strategy optimization for the Atacama Cosmology Telescope

In recent years there have been significant improvements in the sensitivity and the angular resolution of the instruments dedicated to the observation of the Cosmic Microwave Background (CMB). ACTPol is the first polarization receiver for the Atacama Cosmology Telescope (ACT) and is observing the CMB sky with arcmin resolution over 2000 sq. deg. Its upgrade, Advanced ACTPol (AdvACT), will observe the CMB in five frequency bands and over a larger area of the sky. We describe the optimization and implementation of the ACTPol and AdvACT surveys. The selection of the observed fields is driven mainly by the science goals, that is, small angular scale CMB measurements, B-mode measurements and cross-correlation studies. For the ACTPol survey we have observed patches of the southern galactic sky with low galactic foreground emissions which were also chosen to maximize the overlap with several galaxy surveys to allow unique cross-correlation studies. A wider field in the northern galactic cap ensured significant additional overlap with the BOSS spectroscopic survey. The exact shapes and footprints of the fields were optimized to achieve uniform coverage and to obtain cross-linked maps by observing the fields with different scan directions. We have maximized the efficiency of the survey by implementing a close to 24 hour observing strategy, switching between daytime and nighttime observing plans and minimizing the telescope idle time. We describe the challenges represented by the survey optimization for the significantly wider area observed by AdvACT, which will observe roughly half of the low-foreground sky. The survey strategies described here may prove useful for planning future ground-based CMB surveys, such as the Simons Observatory and CMB Stage IV surveys.