We study the case of DM self annihilation , in order to asses its importance as an energy injection mechanism , to the IGM in general , and to the medium within particular DM haloes .
We explain the fact that for thermal relic WIMPS , the annihilation cross section is model independent ( except for possible low velocity enhancements ) , and we consider two well motivated WIMP candidates , the SUSY neutralino and the first KK excited state of the B electroweak boson ( also called the KK-photon ) , that have masses in the range favoured by both , indirect searches and accelerator constraints ( m _ { \chi } \gtrsim 100 GeV ) .
We give an overview of the physical scenarios in which these particles arise , mentioning the motivations and general aspects of the underlying physical theories .
We then analyse in detail the clustering properties of CDM , on all hierarchy levels , from haloes to subhaloes and DM density profiles within them .
In this analysis , we use the Press-Schechter formalism to compute the DM halo mass function , we consider the subhalo mass function calibrated from N-body simulations , and we also consider the process of adiabatical compression by the presence of a SMBH for our computations .
We then explicitly compute the energy output ( or luminosity ) of DM haloes due to annihilations , and compare the obtained luminosities with the standard AGN feedback process , concluding that DM annihilation does not provide the necessary output as to constitute an important feedback mechanism .
We then compute the energy injection rate per baryon of annihilations on the IGM , in order to calculate the effects that it has on its temperature and ionization fraction .
We find significant deviations in the evolutions of the temperature and ionization fraction of the IGM with respect to the adiabatic cooling case , in scenarios that take into account the clustering of DM at all levels , but mainly at z \lesssim 20 , where the IGM evolution would be already driven by PopIII stars .
We conclude that although the DM annihilation can have a significant impact on the properties of the IGM , it can not be regarded as an alternative reionization scenario .
Regarding the detectability of the WIMP through the modifications to the 21 cm differential brightness temperature signal ( \delta T _ { b } ) , we conclude that even considering the adiabatic compression and the substructure , and assuming a maximal absorption fraction of f _ { abs } = 1 , it is not likely that a 1 TeV WIMP with thermal relic cross section may be detected .
However , a lighter 10 GeV WIMP could in principle be detected at the \lesssim 10 mK level at a redshift of \sim 45 , corresponding to a frequency of around 30 MHz .