Light elements were produced in the first minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis.
Among these, deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of relativistic species permeating the early Universe (photons and 3 neutrino families in the standard model).
Although astronomical observations of primordial deuterium abundance have reached percent accuracy, theoretical predictions based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)3He reaction.
The recent measurement of the D(p,γ)3He cross section performed at LUNA lead to a much more accurate BBN prediction of deuterium abundance, improving the BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent cosmic microwave background (CMB) analysis. The LUNA measurement also constrain the amount of “dark radiation”, i.e. relativistic particles not foreseen in the standard model such as sterile neutrinos or hot axions.
In this talk the BBN theory is briefly reviewed and the LUNA results and their consequences in cosmology are discussed.