Cosmological perturbations from inhomogeneous reheating, freeze-out, and mass domination

We generalize a recently proposed mechanism for the origin of primordial metric perturbations in inflationary models. Quantum fluctuations of light scalar fields during inflation gives rise to superhorizon fluctuations of masses and reaction rates of various particles. Reheating, freeze-out, and matter-domination processes become inhomogeneous and generate superhorizon metric perturbations. We also calculate the degree of non-Gaussianity ${f}_{\mathrm{nl}}$ for this new model of cosmological perturbations. The precise value of ${f}_{\mathrm{nl}}$ depends on the specific models, but $|{f}_{\mathrm{nl}}|\ensuremath{\sim}\mathrm{few}$ is a natural lower bound for our mechanisms. This is much larger than the currently assumed theoretical value ${f}_{\mathrm{nl}}\ensuremath{\sim}\mathrm{tilt}\ensuremath{\lesssim}0.05,$ and is thought to be observable. In a particularly attractive model of inhomogeneous mass domination, the non-Gaussianity of perturbations generated by our mechanism is simply ${f}_{\mathrm{nl}}=5,$ irrespective of the detailed structure of the underlying field theory.