Detecting the Neutrinos Mass Hierarchy from Cosmological Data
  We propose a new parameterization to measure the neutrino mass hierarchy,
namely $\Delta=(m_3-m_1)/(m_1+m_3)$ which is dimensionless and varies in the
range $[-1,1]$. Taking into account the results of neutrino oscillation
experiments, $\Delta$ is the unique parameter for determining all the masses of
neutrinos, and a positive (negative) sign of $\Delta$ denotes the normal
(inverted) mass hierarchy. Adopting the currently available cosmic
observations, we find that the normal mass hierarchy is slightly favored, and
the mass of lightest neutrino is less than $0.030$ eV for the normal mass
hierarchy and $0.024$ eV for the inverted mass hierarchy at $95\%$ confidence
level.
