Methods of Discovering New Physics from the Cosmic Neutrino Background

Neutrinos play a significant role in the thermal history of the early universe. The standard cosmological model predicts a relic sea of neutrinos, often referred to as the Cosmic Neutrino Background (CNB). The effects of CNB are parameterized as the effective number of neutrino flavors N eff, which could be measured by indirect astronomy observations. The numerical calculations of the neutrino decoupling process give a result of N eff = 3.046. To measure it with astronomy observations, the primordial abundance of elements from the Big Bang Nucleosynthesis (BBN) and the anisotropies in the distribution of the Cosmic Microwave Background (CMB) are investigated. The observation results basically match the prediction. Direct detection methods are also proposed via capturing neutrinos on a tritium target, which could be practical assuming a large-neutrino-mass cosmological model.