Probing the primordial helium abundance and the effective number of neutrino species with CMB

          @misc{ pirsa_PIRSA:08060175,
            doi = {10.48660/08060175},
            url = {https://pirsa.org/08060175},
            author = {},
            keywords = {Quantum Fields and Strings, Particle Physics, Cosmology},
            language = {en},
            title = {Probing the primordial helium abundance and the effective number of neutrino species with CMB},
            publisher = {Perimeter Institute},
            year = {2008},
            month = {jun},
            note = {PIRSA:08060175 see, \url{https://pirsa.org}}
          }
          

Abstract

We point out that light scalar fields with symmetries generically generate non-Gaussianity in the density fluctuations. Our observation makes the presence of the non-Gaussianity ubiquitous. When the inflationary scale and the properties of the scalar fields satisfy a certain relation, the non-Gaussianity becomes large enough to be observed by the ongoing and planned observations. We name such a particle responsible for a large non-Gaussianity as an \'ungaussiton\', and give explicit examples to realize the ungaussiton mechanism. We also derive a consistency relation between the bispectrum and the trispectrum, tau_NL = 10^3 f_NL^(4/3), which, if confirmed, will strongly support this mechanism.