Recently the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) reported the detection of a 21cm absorption signal stronger than astrophysical expectations. In this paper we study the impact of radiation from dark matter (DM) decay and primordial black holes (PBH) on the 21cm radiation temperature in the reionization epoch, and impose a constraint on the decaying dark matter and PBH energy injection in the intergalactic medium, which can heat up neutral hydrogen gas and weaken the 21cm absorption signal. We consider decay channels DM→ e + e − , γγ, µ + µ − , bb and the 10 15−17 g mass range for primordial black holes, and require the heating of the neutral hydrogen does not negate the 21cm absorption signal. For e + e − , γγ final states and PBH cases we find strong 21cm bounds that can be more stringent than the current extragalactic diffuse photon bounds. For the DM→ e + e − channel, the lifetime bound is τDM > 10 27 s for sub-GeV dark matter. The bound is τDM ≥ 10 26 s for sub-GeV DM→ γγ channel and reaches 10 27 s at MeV DM mass. For bb and µ + µ − cases, the 21 cm constraint is better than all the existing constraints for mDM < 20 GeV where the bound on τDM ≥ 10 26 s. For both DM decay and primordial black hole cases, the 21cm bounds significantly improve over the CMB damping limits from Planck

We investigate constraints on the abundance of primordial black holes (PBHs) in the mass range 10 15 − 10 17 g using data from the Cosmic Microwave Background (CMB) and MeV extragalactic gamma-ray background (EGB). Hawking radiation from PBHs with lifetime greater than the age of the universe leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses ∼ 10 15 − 10 16 g, while the EGB dominates for masses 10 16 g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses ∼ 10 16 − 10 17 g. Planned MeV gamma-ray observatories are ideal for further improving constraints on PBHs in this mass range.

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