Upper Bounds on the Mass of Fundamental Fields from the Primordial Universe

Abstract We study the fluctuations in the vacuum zero-point energy associated with quantum fields and their statistical distributions during inflation. It is shown that the perturbations in the vacuum zero-point energy have large amplitudes that are highly non-Gaussian. The effects of vacuum zero-point fluctuations can be interpreted as the loop corrections in the primordial power spectrum and bispectrum. Requiring that the primordial curvature perturbation remains nearly Gaussian and the loop corrections are under perturbative control imposes strong upper bounds on the mass of fundamental fields during inflation. These bounds depend on the hierarchy of the masses in the theory, such as whether or not the masses are at similar orders. While the mass of the heaviest field in the hierarchy may not be constrained, it is shown that a combination of the masses of the fields cannot be much heavier than the Hubble scale during inflation, otherwise their vacuum zero-point fluctuations induce large non-Gaussianities in primordial perturbations. Considering the observational upper bound on the tensor to scalar ratio, we conclude that this combined mass scale is lighter than 10 14 GeV.