Novel mechanism for CMB modulation in the Standard Model
  We demonstrate that light spectator fields can source sizeable CMB
anisotropies through modulated reheating even in the absence of direct
couplings to the inflaton. The effect arises when the phase space of the
inflaton decay is modulated by the spectator which generates masses for the
decay products. We call the mechanism \textit{indirect modulation} and show
that it can source perturbations even four orders of magnitude larger than the
observed. Importantly, the indirect mechanism is present in the Standard Model
extended with right-handed neutrinos. For a minimally coupled Higgs boson this
leads to a novel lower bound on the quartic coupling and constrains the
neutrino Yukawas below unity.
