Cosmological constraints on exotic injection of electromagnetic energy

By V. Poulin, Julien Lesgourgues, P. Serpico. 2016

242 citations recorded by the source corpus.

We compute cosmic microwave background (CMB) anisotropy constraints on exotic forms of energy injection in electromagnetic (e.m.) channels over a large range of timescales. We show that these constraints are very powerful around or just after recombination, although CMB keeps some sensitivity e.g. to decaying species with lifetimes as long as 1025 s. These bounds are complementary to CMB spectral distortions and primordial nucleosynthesis ones, which dominate at earlier timescales, as we also review here. For the first time, we describe the effects of the e.m. energy injection on the CMB power spectra as a function of the injection epoch, using the lifetime of a decaying particle as proxy. We also identify a suitable on-the-spot approximation, that can be used to derive accurate constraints, and describe its differences with the most up-to-date treatment. Our results are of interest not only for early universe relics constituting (a fraction of) the dark matter, but also for other exotic injection of e.m. radiation. For illustration, we apply our formalism to: i) Primordial black holes of mass 1013.5 g ≲ M ≲ 1016.8 g, showing that the constraints are comparable to the ones obtained from gamma-ray background studies and even dominate below ∼ 1014 g. ii) To a peculiar mass-mixing range in the sterile neutrino parameter space, complementary to other astrophysical and laboratory probes. iii) Finally, we provide a first estimate of the room for improvement left for forthcoming 21 cm experiments, comparing it with the reach of proposed CMB spectral distortion (PiXiE) and CMB angular power spectrum (CORE) missions. We show that the best and most realistic opportunity to look for this signal (or to improve over current constraints) in the 21 cm probe is to focus on the Cosmic Dawn epoch, 15 ≲ z ≲ 30, where the qualitatively unambiguous signature of a spectrum in emission can be expected for models that evade all current constraints.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/3ead7816a43823b79c1f9e008e5e33af6db37cdf

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Citations in the corpus

A Brief Review on Primordial Black Holes as Dark Matter (2021, background): “On the other hand, the energy injection from PBHs evaporation would produce anisotropies and spectral distortions in the CMB spectrum, which would also limit the maximum abundance, leading to similar costraints to those obtained from the extra-galactic c-ray background commented above (Clark et al.,”
The Dawn of FIMP Dark Matter: A Review of Models and Constraints (2017, background): “In the absence of DM thermalization with the visible sector, any such primordial perturbations in the DM density spectrum are not washed out but remain physically observable, leaving an imprint in the CMB.”