Prospects for measuring cosmic microwave background spectral distortions in the presence of foregrounds

Abstract

Measurements of cosmic microwave background spectral distortions have profound implications for our understanding of physical processes taking place over a vast window in cosmological history. Foreground contamination is unavoidable in such measurements and detailed signal-foreground separation will be necessary to extract cosmological science. In this paper, we present MCMC-based spectral distortion detection forecasts in the presence of Galactic and extragalactic foregrounds for a range of possible experimental configurations, focusing on the Primordial Inflation Explorer (PIXIE) as a fiducial concept. We consider modifications to the baseline PIXIE mission (operating 12 months in distortion mode), searching for optimal configurations using a Fisher approach. Using only spectral information, we forecast an extended PIXIE mission to detect the expected average non-relativistic and relativistic thermal Sunyaev-Zeldovich distortions at high significance (194σ and 11σ, respectively), even in the presence of foregrounds. The ΛCDM Silk damping µ-type distortion is not detected without additional modifications of the instrument or external data. Galactic synchrotron radiation is the most problematic source of contamination in this respect, an issue that could be mitigated by combining PIXIE data with future ground-based observations at low frequencies (ν 15 − 30 GHz). Assuming moderate external information on the synchrotron spectrum, we project an upper limit of |µ| < 3.6 × 10 −7 (95% c.l.), slightly more than one order of magnitude above the fiducial ΛCDM signal from the damping of small-scale primordial fluctuations, but a factor of 250 improvement over the current upper limit from COBE/FIRAS. This limit could be further reduced to |µ| < 9.4 × 10 −8 (95% c.l.) with more optimistic assumptions about extra low-frequency information and would rule out many alternative inflation models as well as provide new constraints on decaying particle scenarios.

Polarized anisotropic spectral distortions of the CMB: galactic and extragalactic constraints on photon-axion conversion

“…Upcoming proposed CMB missions like PIXIE [42] would have an instrumental noise of nearly 3 − 4 orders of magnitude better than FIRAS and hence would be able to measure the CMB spectral distortions with an unprecedented accuracy [43]. Measurement of the spectral distortions signal will also depend upon the successful cleaning of the foreground contaminations [41,[44][45][46][47]. Other CMB missions like CORE [48] and LiteBIRD [49] would be able to measure the spatially fluctuating part of the spectral distortions [50] at a much better precision compared to Planck.…”

Primordial non-Gaussianity with μ-type andy-type spectral distortions: exploiting Cosmic Microwave Background polarization and dealing with secondary sources

“…Here we do not account for galactic foregrounds. In [38] it has been shown that the error on the measurement of the spectral distortion monopole can degrade as much as one order of magnitude with respect to earlier, more optimistic estimates. The spatially varying part of these foregrounds will have to be modelled with more accuracy in order to give an actual estimate of how much the estimates will degrade in our case.…”

Exponentially light dark matter from coannihilation

“…Decays of the heavier states can also leave CMB spectral distortions detectable by the proposed PIXIE satellite [154][155][156][157]. Spectral distortions are a generic signal of sterile coannihilation, 1 For the DM mass chosen in the right panel of figure 13, DM annihilations into hadronic final states play an important role and are not treated by MicrOMEGASv4, which works in the partonic limit.…”

“…The bounds are discussed in the text and come from BaBar [150,151], E137 [152], LSND [153], BBN [77,78], and the CMB [154]. The reach for BDX and MiniBooNe adapted from [61], and PIXIE [154][155][156][157] (corresponding to µ < 5 × 10 −8 ) are shown. LDMX [158] can probe the entire allowed region of the left panel, but is not sensitive to the heavier dark photon mass on the right panel.…”