Big Bang Nucleosynthesis

Cosmology and particle physics have recently experienced a revolutionary golden age of discovery. This period has enlightened us to a Universe that is filled with a mix of exotic components. The relative composition of these components is now pinned down to a precision of a few per cent. This effort represents our best current physical description of the Universe; the so-called Standard Model of particle physics and cosmology. Despite this, we currently lack an understanding of the origin of about 99.8% of the current mass-energy budget of the Universe.

An artist's rendering of Big Bang Nucleosynthesis. The temperature and density of the early Universe was so hot that nuclei were fused together for the first time.

Clues about these missing pieces can be found by measuring the relative abundances of the light elements that were forged in the first few minutes after the Big Bang. This process, which is often referred to as Big Bang Nucleosynthesis (BBN), is governed by a competition between the expansion rate of the Universe and the rate at which elements are generated. BBN is one of the only known processes that depends on all four of the known fundamental forces of nature, including gravity, electromagnetism, and the strong and weak interactions. This feature makes BBN a natural testing ground to uncover physics beyond the Standard Model, and to learn the identity of this new physics.

The primordial elements that have received the most attention include the abundances of deuterium (D/H), helium-4 (He/H), helium-3 (3He/H) and lithium-7 (7Li/H). We are acquiring new observations of near-pristine environments to measure some of these abundances to a precision of better than 1 per cent (D/H and He/H).

We are also investigating new avenues to solve the cosmic lithium problem. The current observationally inferred value of the primordial lithium-7 abundance significantly disagrees with the Standard Model value. This could be interpreted as new physics beyond the Standard Model, but could also indicate systematic problems with the current methodology. We are currently performing novel measurements of the lithium abundance to help shed light on this long-standing problem in cosmology.

Staff involved with this topic at Durham include Ryan Cooke.