Cosmological parameter estimation with a joint-likelihood analysis of the cosmic microwave background and big bang nucleosynthesis

We present a joint-likelihood analysis of big bang nucleosynthesis (BBN) and cosmic microwave background (CMB) data, consistently combining likelihoods and taking into account uncertainties in nuclear reaction rates for the first time. Bayesian inference is performed on the baryon abundance and the effective number of neutrino species, Neff, using a CMB Boltzmann solver in combination with LINX, a new flexible and efficient BBN code.We marginalize over Planck nuisance parameters and nuclear rates to find N_eff = 3.08^+0.15_−0.14, 2.94 ^+0.16 _−0.15, or 2.96 ^+0.13 _−0.14, for three separate reaction networks. This framework enables robust testing of the lambda cold dark matter paradigm and its variants with CMB and BBN data.