The evolution of CMB spectral distortions in the early Universe

By J. Chluba, R. Sunyaev, R. Sunyaev. 2011

345 citations recorded by the source corpus.

The energy spectrum of the cosmic microwave background (CMB) allows us to constrain episodes of energy release in the early Universe. In this paper, we revisit and refine computations of the cosmological thermalization problem. For this purpose a new code, called CosmoTherm, was developed that allows us to solve the coupled photon–electron Boltzmann equation in the expanding, isotropic Universe for a small spectral distortion in the CMB. We explicitly compute the shape of the spectral distortions caused by energy release due to (i) annihilating dark matter; (ii) decaying relict particles; (iii) dissipation of acoustic waves; and (iv) quasi-instantaneous heating. We also demonstrate that (v) the continuous interaction of CMB photons with adiabatically cooling non-relativistic electrons and baryons causes a negativeμ-type CMB spectral distortion of ΔIν/Iν∼ 10−8 in the GHz spectral band. We solve the thermalization problem including improved approximations for the double Compton and Bremsstrahlung emissivities, as well as the latest treatment of the cosmological recombination process. At redshifts z≲ 103, the matter starts to cool significantly below the temperature of the CMB so that at very low frequencies, free–free absorption alters the shape of primordial distortions significantly. In addition, the cooling electrons down-scatter CMB photons, introducing a small late negative y-type distortion at high frequencies. We also discuss our results in the light of the recently proposed CMB experiment PIXIE, for which CosmoTherm should allow detailed forecasting. Our current computations show that for energy injection because of points (ii) and (iv), PIXIE should allow us to improve existing limits, while the CMB distortions caused by the other processes seem to remain unobservable with the currently proposed sensitivities and spectral bands of PIXIE.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/15ea29821527ee0cfbcffafa942fd7a5eb689a6d

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Citations in the corpus

Gravitational waves at interferometer scales and primordial black holes in axion inflation (2016, background): “μ−distortions are mostly affected by primordial perturbations of wavenumbers 50 Mpc−1 <∼ k <∼ 10 4 Mpc−1 [62, 64], which roughly corresponds to modes that left the horizon at 45 <∼ N <∼ 50 e-folds before the end of inflation (as in the rest of the paper, this assumes that the Planck pivot scale k = ”
CMB at 2 × 2 order: the dissipation of primordial acoustic waves and the observable part of the associated energy release (2012, methodology): “Although acoustic dissipation creates a mixture of µ andy-type distortions (Chluba & Sunyaev 2012), theµ-type contribution is especially important since it can only be introduced at redshifts 5× 104 . z .”
PRISM (Polarized Radiation Imaging and Spectroscopy Mission): an extended white paper (2013, background): “ [13,162,200]. This observation places very tight constraints on the thermal history of our universe, ruling out cosmologies with extended periods of signiﬁcant energy release at redshifts z. few 106 [26,33,43,57,99,105,111,203,222]. However a large number of astrophysical and cosmological processes”
PROBING THE INFLATON: SMALL-SCALE POWER SPECTRUM CONSTRAINTS FROM MEASUREMENTS OF THE COSMIC MICROWAVE BACKGROUND ENERGY SPECTRUM (2012, methodology): “An interpretation of a detection of CMB spectral distortion therefore requires more careful consideration of the differences (e.g., the mixture betweenµ andy; the detailed shape of the distortion at low frequencies) in the distortions foreach case, which in principle can be accurately computed using”
The landscape of QCD axion models (2020, background): “Early energy release from decays with lifetimes ∼ (10 ÷ 10) s is strongly constrained also by limits on CMB spectral distortions [530–532].”
Cosmological constraints on exotic injection of electromagnetic energy (2016, background): “The visibility functions are given by [38]”
Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, neutral): “…the cyclotron process, which, depending on the amplitude of PMFs, could in principle play a role in the generation and evolution of spectral distortions and in particular in the thermalization process (for a general overview see Burigana et al. 1991; Hu & Silk 1993; and Chluba & Sunyaev 2012).”