Cosmological Backgrounds of Gravitational Waves and eLISA/NGO: Phase
  Transitions, Cosmic Strings and Other Sources
  We review several cosmological backgrounds of gravitational waves accessible
to direct-detection experiments, with a special emphasis on those backgrounds
due to first-order phase transitions and networks of cosmic (super-)strings.
For these two particular sources, we revisit in detail the computation of the
gravitational wave background and improve the results of previous works in the
literature. We apply our results to identify the scientific potential of the
NGO/eLISA mission of ESA regarding the detectability of cosmological
backgrounds.
