Constraints on Dark Matter annihilations from reionization and heating of the intergalactic gas
Jul, 2009
22 pages
Published in:
- JCAP 10 (2009) 009
e-Print:
- 0907.0719 [astro-ph.CO]
Report number:
- SACLAY-T09-065
View in:
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Abstract: (arXiv)
Dark Matter annihilations after recombination and during the epoch of structure formation deposit energy in the primordial intergalactic medium, producing reionization and heating. We investigate the constraints that are imposed by the observed optical depth of the Universe and the measured temperature of the intergalactic gas. We find that the bounds are significant, and have the power to rule out large portions of the `DM mass/cross section' parameter space. The optical depth bound is generally stronger and does not depend significantly on the history of structure formation. The temperature bound can be competitive in some cases for small masses or the hadronic annihilation channels (and is affected somewhat by the details of structure formation). We find in particular that DM particles with a large annihilation cross section into leptons and a few TeV mass, such as those needed to explain the PAMELA and FERMI+HESS cosmic ray excesses in terms of Dark Matter, are ruled out as they produce too many free electrons. We also find that low mass particles (<~ 10 GeV) tend to heat too much the gas and are therefore disfavored.Note:
- 22 pages, 5 figures
- dark matter: annihilation
- lepton: production
- dark matter: mass
- gas: ionization
- gas: temperature
- PAMELA
- HESS
- galaxy: formation
- parameter space
- numerical calculations
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