Thermal Perturbations from Cosmological Constant Relaxation
  We probe the cosmological consequences of a recently proposed class of
solutions to the cosmological constant problem. In these models, the universe
undergoes a long period of inflation followed by a contraction and a bounce
that sets the stage for the hot big bang era. A requirement of any successful
early universe model is that it must reproduce the observed scale-invariant
density perturbations at CMB scales. While these class of models involve a long
period of inflation, the inflationary Hubble scale during their observationally
relevant stages is at or below the current Hubble scale, rendering the de
Sitter fluctuations too weak to seed the CMB anisotropies. We show that
sufficiently strong perturbations can still be sourced thermally if the
relaxion field serving as the inflaton interacts with a thermal bath, which can
be generated and maintained by the same interaction. We present a simple model
where the relaxion field is derivatively (i.e. technically naturally) coupled
to a non-abelian gauge sector, which gets excited tachyonically and
subsequently thermalizes due to its nonlinear self-interactions. This model
explains both the smallness of the cosmological constant and the amplitude of
CMB anisotropies.
