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 \rightarrow e ^ { + } e ^ { - } , \gamma \gamma , \mu ^ { + } \mu ^ { - } , b \bar { b } 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 ^ { - } , \gamma \gamma 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 \rightarrow e ^ { + } e ^ { - } channel , the lifetime bound is \tau _ { DM } > 10 ^ { 27 } s for sub-GeV dark matter .
The bound is \tau _ { DM } \geq 10 ^ { 26 } s for sub-GeV DM \rightarrow \gamma \gamma channel and reaches 10 ^ { 27 } s at MeV DM mass .
For b \bar { b } and \mu ^ { + } \mu ^ { - } cases , the 21 cm constraint is better than all the existing constraints for m _ { DM } < 20 GeV where the bound on \tau _ { DM } \geq 10 ^ { 26 } s. For both DM decay and primordial black hole cases , the 21cm bounds significantly improve over the CMB damping limits from Planck data .