Cosmological constraints on exotic injection of electromagnetic energy

• Published in: Journal of cosmology and astroparticle physics Vol. 2017; no. 3; p. 43
• Main Authors: Poulin, Vivian, Lesgourgues, Julien, Serpico, Pasquale D.
• Format: Journal Article
• Language: English
• Published: United States Institute of Physics (IOP) 21.03.2017
• Subjects: ANISOTROPY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; COMPARATIVE EVALUATIONS; COSMOLOGICAL MODELS; Cosmology and Extra-Galactic Astrophysics; EMISSION; GAMMA RADIATION; INJECTION; LIFETIME; MASS; NONLUMINOUS MATTER; NUCLEOSYNTHESIS; Physics; RECOMBINATION; RELICT RADIATION; SENSITIVITY; SPACE; SPECTRA; STERILE NEUTRINOS; UNIVERSE
• ISSN: 1475-7516; 1475-7508; 1475-7516
• DOI: 10.1088/1475-7516/2017/03/043

We compute cosmic microwave background (CMB) anisotropy constraints on exoticforms of energy injection in electromagnetic (e.m.) channels over a large rangeof timescales. These constraints are very powerful around or just afterrecombination, although CMB keeps some sensitivity e.g. to decaying specieswith lifetimes as long as $10^{25}\,$s. We review here complementary with CMBspectral distortions and primordial nucleosynthesis bounds, which dominate atearlier timescales. 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 identify a suitableon-the-spot approximation. Our results are of interest not only for earlyuniverse relics constituting (a fraction of) the dark matter, but also forother exotic injection of e.m. radiation. For illustration, we apply ourformalism to: i) Primordial black holes of mass $\in [10^{13.5},10^{16.8}]$ g,showing that the constraints are comparable to the ones obtained from gamma-raybackground studies and even dominate below $\sim 10^{14}$g. ii) To a peculiarmass-mixing range in the sterile neutrino parameter space, complementary toother astrophysical and laboratory probes. iii) Finally, we provide a firstestimate of the room for improvement left for forthcoming 21 cm experiments,comparing it with the reach of proposed CMB spectral distortion (PiXiE) and CMBangular power spectrum (CORE) missions. We show that the best and mostrealistic opportunity to look for this signal (or to improve over currentconstraints) in the 21 cm probe is to focus on the Cosmic Dawn epoch,$15\lesssim z\lesssim30$, where the qualitatively unambiguous signature of aspectrum in emission can be expected for models that evade all currentconstraints.