Breaking the Single Clock Symmetry: measuring single-field inflation
  non-Gaussian features
  The Universe is not just cold dark matter and dark energy, it also contains
baryons, radiation and neutrinos. The presence of these components, beyond the
pressure-less cold dark matter and the quasi-uniform dark energy ones, imply
that the single clock assumption from inflation is no longer preserved. Here we
quantify this effect and show that the single-clock symmetry is ensured only on
scales where baryonic effects, neutrinos effects, or sound speed are zero.
These scales depend on the cosmic epoch and the Universe composition. Hence for
all use and purposes of interpreting state-of-the-art and possibly forthcoming
surveys, in the accessible scales, single clock symmetry cannot be said to be
satisfied. Breaking the single-clock symmetry has key consequences for the
study of non-Gaussian features generated by pure single-field inflation which
arise from non-linearities in the metric yielding non-Gaussianities of the
local type: the $n_{s}-1$ and the relativistic $-5/3$ term.
