Title: Planck 2014 Constraints on the Cosmic Neutrino(-like) Background"


The Planck 2014 results include the tightest measurements to-date of cosmic microwave background (CMB) temperature and polarization anisotropies up to few-arcminute angular scales. I will give a broad overview of the cosmology results from these data, with particular focus on what we have learned about the cosmic neutrino background (CNB). The new data allow more precise answers to questions such as 1) how much energy, parameterized by N_eff, is contained in the CNB? 2) what is the sum of the masses of the particles making up the CNB? and 3) are these particles really neutrinos, i.e. do they free-stream like neutrinos? One possibility I will explore is if some component of the CNB actually comes from axions or axion-like particles. Recent improvements in CMB and BBN data are shedding new light on this scenario. Finally, I will discuss the status of agreement between Planck results and other cosmological probes such as BAO, H0, and low redshift structure measurements, and how the CNB may play a role in resolving tensions between some of them. `