A new determination of the primordial helium abundance

Resumen

We present new Y values for five H II regions, from these values we determine the primordial helium abundance, Y_P, and obtain that Y_P = 0.2446 ± 0.0029, (Peimbert, A. et al. 2016, RMxAA, 52, 419). The main difference of our new value with the Y_P value by Peimbert, M. et al. (2007, ApJ , 666, 633) is due to the use of updated atomic physics parameters. Our Y_P value is consistent with that by Aver, E. et al. (2015, JCAP, 7, 11), that amounts to Y_P = 0.2449 ± 0.0040, but in disagreement by more than 3σ with that by Izotov, Y. I. et al. (2014, MNRAS, 443, 778), that amounts to Y_P = 0.2551 ± 0.0022. Y_P together with Big Bang Nucleosynthesis, BBN, can be used to put constraints on the number of neutrino families, N_ν, and the neutron mean life, τ_n. The adoption of a neutron mean life of τ_n = 880.3 ± 1.1 (s) (Olive, K. A et al. 2014, Chinese Physics C, 38, 090001) and our Y_P value imply that N_eff = 2.90 ± 0.22, consistent with 3 neutrino families but not with 4 neutrino families. The adoption of N_eff = 3.046 (Mangano, G. and Serpico, P. D. 2011, PhLB, 701, 296) and our Y_P value imply that τ_n = 872 ± 14 (s), consistent with both high and low values of τ_n in the literature. An increase on the quality of the Y_P determination from H II regions will provide stronger constraints on the N_ν and τ_n values.