The Effective Planck Mass and the Scale of Inflation
  Observable quantities in cosmology are dimensionless, and therefore
independent of the units in which they are measured. This is true of all
physical quantities associated with the primordial perturbations that source
cosmic microwave background anisotropies such as their amplitude and spectral
properties. However, if one were to try and infer an absolute energy scale for
inflation-- a priori, one of the more immediate corollaries of detecting
primordial tensor modes-- one necessarily makes reference to a particular
choice of units, the natural choice for which is Planck units. In this note, we
discuss various aspects of how inferring the energy scale of inflation is
complicated by the fact that the effective strength of gravity as seen by
inflationary quanta necessarily differs from that seen by gravitational
experiments at presently accessible scales. The uncertainty in the former
relative to the latter has to do with the unknown spectrum of universally
coupled particles between laboratory scales and the putative scale of
inflation. These intermediate particles could be in hidden as well as visible
sectors or could also be associated with Kaluza-Klein resonances associated
with a compactification scale below the scale of inflation. We discuss various
implications for cosmological observables.
