Improving The Primordial Helium Abundance Measurement

The primordial helium abundance (Y_p) is one of the fundamental products of the early universe and, correspondingly, offers a unique window into the content and interactions of the universe in the first minutes after the big bang. The primordial helium abundance is sensitive to several cosmological parameters, and, most importantly, the effective number of relativistic degrees of freedom in the early universe, often parameterized in terms of the effective number of neutrino flavors. Using measurements from the cosmic microwave background and assuming the standard model of particle physics and cosmology, big bang nucleosynthesis now predicts the initial elemental composition of the universe with high precision. A high precision, accurate measurement of Y_p is required to test the prediction. However, observational determinations based on spectral observations of H II regions are complicated by systematic effects. I will discuss recent improvements in these determinations. These include improving our methodologies, expanding and updating our physical model, improving self-consistency, and employing Markov Chain Monte Carlo to facilitate more rigorous statistical treatment of the uncertainty. Enabled by higher resolution and broader wavelength coverage spectra, recent efforts have shown significant gains in reducing uncertainties from the incorporation of additional emission lines, including higher order Balmer lines, Paschen lines, and the IR emission line He I λ10380.