New BBN limits on physics beyond the standard model from 4He

A recent analysis of the 4He abundance determined from observations of extragalactic HII regions indicates a significantly greater uncertainty for the 4He mass fraction. Furthermore, due to a different treatment of systematic effects such as underlying stellar absorption, the derived value of the 4He abundance is slightly higher. As a result, the predicted value of the primordial 4He abundance is now in line with calculations from big bang nucleosynthesis when the baryon density determined by WMAP is assumed. Analysis based on prior estimates of the 4He abundance will necessarily lead to constraints which are overly restrictive. Based on this new analysis of 4He, we derive constraints on a host of particle properties which include: limits on the number of relativistic species at the time of BBN (commonly taken to be the limit on neutrino flavors), limits on the variations of fundamental couplings such as αem and GN, and limits on decaying particles.