The extragalactic background light revisited and the cosmic
  photon-photon opacity
  In addition to its relevant astrophysical and cosmological significance, the
Extragalactic Background Light (EBL) is a fundamental source of opacity for
cosmic high energy photons, as well as a limitation for the propagation of
high-energy particles in the Universe. We review our previously published
determinations of the EBL photon density in the Universe and its evolution with
cosmic time, in the light of recent surveys of IR sources at long wavelengths.
We exploit deep survey observations by the Herschel Space Observatory and the
Spitzer telescope, matched to optical and near-IR photometric and spectroscopic
data, to re-estimate number counts and luminosity functions longwards of a few
microns, and the contribution of resolved sources to the EBL. These new data
indicate slightly lower photon densities in the mid- and far-infrared and
sub-millimeter compared to previous determinations. This implies slightly lower
cosmic opacity for photon-photon interactions. The new data do not modify
previously published EBL modeling in the UV-optical and near-IR up to several
microns, while reducing the photon density at longer wavelengths. This improved
model of the EBL alleviates some tension that had emerged in the interpretation
of the highest-energy TeV observations of local \textit{blazar}s, reducing the
case for new physics beyond the standard model (like violations of the Lorenz
Invariance, LIV, at the highest particle energies), or for exotic astrophysics,
that had sometimes been called for to explain it. Applications of this improved
EBL model on current data are considered, as well as perspectives for future
instrumentation, the Cherenkov Telescope Array (CTA) in particular.
