Description
Fields that couple to the visible sector only gravitationally remain firmly out of reach of all collider and direct detection experiments for the foreseeable future. Unless these so called hidden fields influence the expansion and clustering history of the universe (i.e. constitute dark matter), the same might seem to be true for cosmological observations as well. In this talk we will review how this is not entirely the case. Hidden fields (even if they are energetically subdominant) can exert a range of effects in the early universe through their influence on the effective strength of gravitational interactions at high energies. In the context of inflationary cosmology, we show how their presence can affect the inferred energy scale of inflation, and if present in large numbers can also generate large non-Gaussianties in the context of single field inflation (away from the so-called squeezed configuration). Thus, one can convert ever more precise bounds on the amount of primordial non-Gaussianity present in the CMB into bounds on the hidden field content of the universe.
