Abstract

Neutrinos and new light particles, which arise in many extensions of the Standard Model of particle physics, are an important probe of the (thermal) history of the universe. However, they are hard to detect in terrestrial experiments due to their weak couplings to ordinary matter. The high temperatures in the early universe allow an efficient production of even very weakly-coupled particles which makes it possible to measure their gravitational effects in cosmological observations. I will discuss the sensitivity of future cosmic microwave background and large-scale structure observations to constrain the radiation density and detect these particles, which will probe the universe when it was younger than one second. In addition, I will present the first measurement of the cosmic neutrino background as imprinted in the baryon acoustic oscillation spectrum obtained by BOSS .