We calculate the reionization history for different models of the stellar population and explore the effects of primordial magnetic fields , dark matter decay and dark matter annihilation on reionization .
We find that stellar populations based on a Scalo-type initial mass function for Population II stars can be ruled out as sole sources for reionization , unless star formation efficiencies of more than 10 \% or very high photon escape fractions from the parental halo are adopted .
When considering primordial magnetic fields , we find that the additional heat injection from ambipolar diffusion and decaying MHD turbulence has significant impact on the thermal evolution and the ionization history of the post-recombination universe and on structure formation .
The magnetic Jeans mass changes the typical mass scale of the star forming halos , and depending on the adopted stellar model we derive upper limits to the magnetic field strength between 0.7 and 5 nG ( comoving ) .
For dark matter annihilation , we find an upper limit to the thermally averaged mass-weighted cross section of \langle \sigma v \rangle / m _ { DM } \leq 10 ^ { -33 } \mathrm { cm } ^ { 3 } \mathrm { / s / eV } .
For dark matter decay , our calculations yield a lower limit to the lifetime of dark matter particles of \tau \geq 3 \times 10 ^ { 23 } s. These limits are in agreement with constraints from recombination and provide an independent confirmation at a much later epoch .