COrE (Cosmic Origins Explorer) A White Paper

TL;DR

COrE seeks to advance cosmology and Galactic astrophysics by performing full-sky, multi-band polarization measurements with unprecedented sensitivity and angular resolution. Its core strategy combines broad spectral coverage across 15 bands, a rotating polarization modulator, and large detector arrays to enable robust separation of CMB from foregrounds, enabling detection of primordial B-modes down to $r\sim 10^{-3}$ and precise CMB lensing measurements. The mission framework encompasses inflationary physics, neutrino masses, non-Gaussianity, reionization history, magnetic fields, and extragalactic source populations, while delivering transformative Galactic maps of dust and synchrotron polarization. If realized, COrE would provide a near-complete laboratory for early-Universe physics and a detailed, Faraday-rotation-free view of the Galaxy, with broad implications for fundamental physics and cosmology.

Abstract

COrE (Cosmic Origins Explorer) is a fourth-generation full-sky, microwave-band satellite recently proposed to ESA within Cosmic Vision 2015-2025. COrE will provide maps of the microwave sky in polarization and temperature in 15 frequency bands, ranging from 45 GHz to 795 GHz, with an angular resolution ranging from 23 arcmin (45 GHz) and 1.3 arcmin (795 GHz) and sensitivities roughly 10 to 30 times better than PLANCK (depending on the frequency channel). The COrE mission will lead to breakthrough science in a wide range of areas, ranging from primordial cosmology to galactic and extragalactic science. COrE is designed to detect the primordial gravitational waves generated during the epoch of cosmic inflation at more than $3σ$ for $r=(T/S)>=10^{-3}$. It will also measure the CMB gravitational lensing deflection power spectrum to the cosmic variance limit on all linear scales, allowing us to probe absolute neutrino masses better than laboratory experiments and down to plausible values suggested by the neutrino oscillation data. COrE will also search for primordial non-Gaussianity with significant improvements over Planck in its ability to constrain the shape (and amplitude) of non-Gaussianity. In the areas of galactic and extragalactic science, in its highest frequency channels COrE will provide maps of the galactic polarized dust emission allowing us to map the galactic magnetic field in areas of diffuse emission not otherwise accessible to probe the initial conditions for star formation. COrE will also map the galactic synchrotron emission thirty times better than PLANCK. This White Paper reviews the COrE science program, our simulations on foreground subtraction, and the proposed instrumental configuration.

Figures (30)

• Figure 1: Inflationary prediction for the CMB temperature and polarization anisotropies for the scalar and tensor modes. The horizontal axis indicates the multipole number $\ell$ and the vertical axis indicates $\ell (\ell +1)C_\ell ^{AB}/(2\pi )$ in units of $(\mu K)^2$, which is roughly equivalent to the derivative of the power spectrum with respect to $\ln\ell$. The green curves indicate the TT, TE, and EE power spectra (from top to bottom) generated by the scalar mode assuming the parameters from the best-fit model from WMAP seven-year data ($H_0=71.4\,{\rm km~s^{-1}~Mpc^{-1}}$, $\Omega_b=0.045$, $\Omega_{cdm}=0.220$, $\Omega_{\Lambda }=0.73$, $\tau =0.086$, and $n_s=0.969$). The BB scalar component (indicated by the heavy red curve) results from the gravitational lensing of the EE polarized CMB anisotropy at the last scattering surface $z\approx 1100$ by structures situated mainly around redshift $z\approx 2$. The top three blue curves (from top to bottom on the left) indicate the TT, TE, BB, and EE spectra resulting from the tensor mode assuming a scale-invariant ($n_T=0$) primordial spectrum and a tensor-to-scalar ratio $(T/S)$ of $0.1$, and the solid black curves indicate the BB spectra for the descending values of $(T/S)=r=0.1, 0.01, 0.001$ and $0.0001.$ For the TE cross-correlations we have plotted the log of the absolute value, hence the downward spikes which correspond to sign changes.
• Figure 2: CMB scalar and tensor anisotropies relative to PLANCK and COrE sensitivities We show again the scalar (blue and red) and tensor (black) anisotropies but now together with the PLANCK and CORE instrument noise in brown and magenta, respectively. The scalar anisotropies are the TT (top) and EE (bottom) spectra in blue and a BB lensing contribution (in red). These are relatively certain. The BB is shown for $r$ of $0.1,$$0.01$ and $0.001$ in black (top to bottom). The solid brown and magenta curves show the instrument noise power spectra for PLANCK and COrE, and the dashed counterparts below indicate what sensitivity can be obtained by wide binning $(\Delta \ell )/\ell \approx 1.$ Modes of the CMB spectra lying above the solid noise curves are detected with $(S/N)\mathrel{\hbox{$>$}\mkern-14mu \hbox{$\sim$}} 1,$ implying that measurements at higher instrumental sensitivity would result in marginal additional science value. On the other hand, CMB spectra lying between the solid and dashed sensitivity give a signal detectable when many modes are combined in the analysis. We see that for $\ell \mathrel{\hbox{$<$}\mkern-14mu \hbox{$\sim$}} 800$ PLANCK the $C_{EE}$ measurements oscillate in and out of the $(S/N)=1$ threshold while for COrE modes up to $\ell \approx 2000$ are resolved with $(S/N)\gg 1.$ This means that for studies of non-Gaussianity one has about ten times as many resolution elements.
• Figure 3: Constraints on inflation from COrE. For a broad range of inflationary models COrE can be expected to detect primordial gravitational waves from inflation. The large contours on the left panel show the present constraints from WMAP seven-year data in the $r$-$n_S$ plane. A few parameterized families of inflationary models give an idea of representative model predictions. The small contours illustrate what a COrE detection would look like if $r >5\times 10^{-3}$. The part of parameter space still allowed at 2$\sigma$ in the case of a non-detection is shown in grey. The right panel shows the 'main sequence' of inflationary models generated using a model independent approach.
• Figure 4: Forecast $1$, $2$ and $3\sigma$ joint constraints in the $r$-$n_S$ plane including the effects of foreground subtraction errors. The consistency relation has been imposed. All other cosmological parameters have been marginalized over. The ellipses on the left side correspond to component separation with a large galactic mask blanking out the galaxy at galactic latitudes $|b| \leq 20^\circ$ ($f_{\rm sky} = 65$%), for $r=0.001$ and $n_s=0.96$. Ellipses centered around $r=0.005$ and $n_s=0.96$ correspond to a case with five times larger B modes, analyzed with a smaller galactic mask ($f_{\rm sky} = 70$%, dotted contours) or with the same mask as in the case $r=0.001$ ($f_{\rm sky} = 65$%, solid contours).
• Figure 5: Lensing reconstruction noise on the deflection power spectrum for an extended PLANCK mission (24 months; left) and COrE (right) using temperature alone (red) and temperature and polarization (blue). For COrE, we also show the approximate noise level (green) for an improved iterative version of the reconstruction estimator following Ref. lens:cmbpol_stud. The deflection power spectrum is also plotted based on the linear matter power spectrum (black solid) and with non-linear corrections (black dashed). The maximum multipole used in the reconstruction is $l_{\mathrm{max}}=2500$.