Do We Need Stars to Reionize the Universe at High Redshifts? Early Reionization by Decaying Heavy Sterile Neutrinos

Details Do We Need Stars to Reionize the Universe at High Redshifts? Early Reionization by Decaying Heavy Sterile Neutrinos Do We Need Stars to Reionize the Universe at High Redshifts? Early Reionization by Decaying Heavy Sterile Neutrinos

2003-05-08

arxiv.org/abs/astro-ph/0305126v3

Astrophys.J.600:26-31,2004

Astronomy and Astrophysics

Astrophysics

Improved the discussion of electron-CMB interaction; describe the reionization process in more detail; conclusions unchanged;

Scientific paper

10.1086/379636

A remarkable result of the Wilkinson Microwave Anisotropy Probe (WMAP) observations is that the universe was significantly reionized at large redshifts. The standard explanation is that massive stars formed early and reionized the universe around redshift z=17. Here we explore an alternative possibility, in which the universe was reionized in two steps. An early boost of reionization is provided by a decaying sterile neutrino, whose decay products, relativistic electrons, result in partial ionization of the smooth gas. We demonstrate that a neutrino with a mass of m_nu ~ 200 MeV and a decay time of t ~ 4 * 10^{15} s can account for the electron scattering optical depth tau=0.16 measured by WMAP without violating existing astrophysical limits on the cosmic microwave and gamma ray backgrounds. Reionization is then completed by subsequent star formation at lower redshifts. This scenario alleviates constraints on structure formation models with reduced small-scale power, such as those with a running or tilted scalar index, or warm dark matter models.

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