Searching for sterile neutrinos in dynamical dark energy cosmologies
  We investigate how the dark energy properties change the cosmological limits
on sterile neutrino parameters by using recent cosmological observations. We
consider the simplest dynamical dark energy models, the $w$CDM model and the
holographic dark energy (HDE) model, to make an analysis. The cosmological
observations used in this work include the Planck 2015 CMB temperature and
polarization data, the baryon acoustic oscillation data, the type Ia supernova
data, the Hubble constant direct measurement data, and the Planck CMB lensing
data. We find that, $m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.2675$ eV and $N_{\rm
eff}<3.5718$ for $\Lambda$CDM cosmology,
$m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.5313$ eV and $N_{\rm eff}<3.5008$ for
$w$CDM cosmology, and $m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.1989$ eV and $N_{\rm
eff}<3.6701$ for HDE cosmology, from the constraints of the combination of
these data. Thus, without the addition of measurements of growth of structure,
only upper limits on both $m_{\nu,{\rm{sterile}}}^{\rm{eff}}$ and $N_{\rm eff}$
can be derived, indicating that no evidence of the existence of a sterile
neutrino species with eV-scale mass is found in this analysis. Moreover,
compared to the $\Lambda$CDM model, in the $w$CDM model the limit on
$m_{\nu,{\rm{sterile}}}^{\rm{eff}}$ becomes much looser, but in the HDE model
the limit becomes much tighter. Therefore, the dark energy properties could
significantly influence the constraint limits of sterile neutrino parameters.
