Dark Radiation and Decaying Matter
  Recent cosmological measurements favour additional relativistic energy
density beyond the one provided by the three active neutrinos and photons of
the Standard Model (SM). This is often referred to as "dark radiation",
suggesting the need of new light states in the theory beyond those of the SM.
In this paper, we study and numerically explore the alternative possibility
that this increase comes from the decay of some new form of heavy matter into
the SM neutrinos. We study the constraints on the decaying matter density and
its lifetime, using data from the Wilkinson Microwave Anisotropy Probe, the
South Pole Telescope, measurements of the Hubble constant at present time, the
results from high-redshift Type-I supernovae and the information on the Baryon
Acoustic Oscillation scale. We, moreover, include in our analysis the
information on the presence of additional contributions to the expansion rate
of the Universe at the time of Big Bang Nucleosynthesis. We compare the results
obtained in this decaying matter scenario with those obtained with the standard
analysis in terms of a constant $N_{\rm eff}$.
