Exploring cosmic origins with CORE: Survey requirements and mission design

Abstract

Future observations of cosmic microwave background (CMB) polarisation have the potential to answer some of the most fundamental questions of modern physics and cosmology, including: What physical process gave birth to the Universe we see today? What are the dark matter and dark energy that seem to constitute 95% of the energy density of the Universe? Do we need extensions to the standard model of particle physics and fundamental interactions? Is the ΛCDM cosmological scenario correct, or are we missing an essential piece of the puzzle? In this paper, we list the requirements for a future CMB polarisation survey addressing these scientific objectives, and discuss the design drivers of the CORE space mission proposed to ESA in answer to the "M5" call for a medium-sized mission. The rationale and options, and the methodologies used to assess the mission's performance, are of interest to other future CMB mission design studies. CORE has 19 frequency channels, distributed over a broad frequency range, spanning the 60-600 GHz interval, to control astrophysical foreground emission. The angular resolution ranges from 2 to 18 , and the aggregate CMB sensitivity is about 2 µK.arcmin. The observations are made with a single integrated focal-plane instrument, consisting of an array of 2100 cryogenically-cooled, linearly-polarised detectors at the focus of a 1.2-m aperture cross-Dragone telescope. The mission is designed to minimise all sources of systematic effects, which must be controlled so that no more than 10 −4 of the intensity leaks into polarisation maps, and no more than about 1% of E-type polarisation leaks into B-type modes. CORE observes the sky from a large Lissajous orbit around the Sun-Earth L2 point on an orbit that offers stable observing conditions and avoids contamination from sidelobe pick-up of stray radiation originating from the Sun, Earth, and Moon. The entire sky is observed repeatedly during four years of continuous scanning, with a combination of three rotations of the spacecraft over different timescales. With about 50% of the sky covered every few days, this scan strategy provides the mitigation of systematic effects and the internal redundancy that are needed to convincingly extract the primordial B-mode signal on large angular scales, and check with adequate sensitivity the consistency of the observations in several independent data subsets. CORE is designed as a "near-ultimate" CMB polarisation mission which, for optimal complementarity with ground-based observations, will perform the observations that are known to be essential to CMB polarisation science and cannot be obtained by any other means than a dedicated space mission. It will provide well-characterised, highly-redundant multi-frequency observations of polarisation at all the scales where foreground emission and cosmic variance dominate the final uncertainty for obtaining precision CMB science, as well as 2 angular resolution maps of high-frequency foreground emission in the 300-600 GHz frequency range, essential for complementarity w...

Cornering the Planck Alens tension with future CMB data

“…We have considered several future experiments with technical specifications listed in Table II. In particular, we have considered three possible CMB satellite experiments, CORE [23,26], LiteBIRD [27] and PIXIE [28]. A stage-III experiment in two possible configurations as in [24], i.e., a wide experiment similar to AdvACT and a deep experiment similar to SPT-3G.…”

Status of Neutrino Properties and Future Prospects—Cosmological and Astrophysical Constraints

“…Measurements of the power spectrum of CMB anisotropies in temperature are cosmic-variance limited down to very small scales (ℓ ∼ 1, 500) and the quality of current CMB data in polarization is already good enough to tighten constraints on cosmological parameters [14,16,17,19,20]. The next generation of CMB experiments will further improve our knowledge of CMB polarization anisotropies [21,[30][31][32][33]. The main systematics involved in CMB measurements are due to foreground contamination (atmospheric, galactic, extragalactic), calibration uncertainties and spurious effects induced by an Bounds given in this table are 95% CL.…”

“…The mission, named Cosmic ORigin Explorer (CORE), is designed to have 19 frequency channels in the range 60 − 600 GHz for simultaneously solving for CMB and foreground signals, angular resolution in the range 2 ′ − 18 ′ depending on the frequency channel and aggregate sensitivity of 2 µK · arcmin [32] (for comparison, the Planck satellite has 9 frequency channels in the range 30 − 900 GHz, angular resolution in the range 5 ′ − 33 ′ and the most sensitive channel shows a temperature noise of 0.55 µK · deg at 143 GHz [135]). This experimental setup would enable to constrain m ν = (0.072 +0.037 −0.051 ) eV at 68% CL assuming a CDM model with a fiducial value of the sum of the neutrino masses m ν = 0.06 eV, for the combination of CORE TT,TE,EE,PP (temperature and E-polarization auto and cross spectra and lensing power spectrum PP) [132].…”

“…The greatest contaminant for a ground-based experiment is the atmospheric noise, which highly reduces the accessible frequencies for CMB observations to a total of four windows, roughly 35, 90, 150, and 250 GHz. The main advantages with respect to a spaceborne mission are a larger collecting area with an incredibly higher number of detectors (for a comparison, the CORE proposal accounts for a total of 2,100 detectors [32], the Planck satellite has 74 detectors [135]) and subsequent suppression of experimental noise. At large scales, the Stage-IV target is the recombination bump at ℓ > 20.…”

“…Future CMB missions-including Advanced ACTPol [28], SPT-3G [29], CMB Stage-IV [30], Simons Observatory 1 , Simons Array [31], CORE [32], LiteBIRD [33], PIXIE [34]-will test the Universe over a wide range of scales with unprecedented accuracy. The same accuracy will enable the reconstruction of the weak lensing signal from the CMB maps down to the smallest scales and with high sensitivity, providing an additional probe of the distribution and evolution of structures in the universe.…”