Catalyzing Primordial Nuclear Chemistry

One of the principal predictions of the standard big bang model is the creation of light nuclei-heavy hydrogen (deuterium), helium-3 and -4 and lithium-6 and -7, in the minutes and hours after the big bang itself. Understanding big bang nucleosynthesis (BBN) is important since it corresponds to the earliest epoch in the early universe for which observation and theory can be tested against each other (the creation of the first stable compound nuclei comes long before the first creation of stable atoms).

Agreement between observations and predictions has been pretty good so far, with the predictions being sharpened in recent years by high-precision maps of the cosmic microwave background. Furthermore, the measurements of elemental abundances can be used to look for phenomena beyond known physics. Indeed, some cosmic abundance studies have already set limits on the number of additional light particles and most recently on the nature of hypothetical extra spatial dimensions.

But a remaining puzzle is the amount of primordial lithium; both Li-6 and Li-7 are unexpectedly abundant in metal-poor stars (those with very few heavier elements). For example, a much higher than expected level of Li-6 might be pointing to a primordial origin (that is, not made later in stellar cores or in supernovas), in which case the BBN model would need to be amended. Maxim Pospelov (pospelov@uvic.ca) of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, and University of Victoria, British Columbia suggests that the anomaly can be explained if early nucleosynthesis was aided---catalyzed---by the presence of charged heavy particles, which are common in many models of particle physics.

In fact such particles are suggested in supersymmetry (SUSY for short) theories. In the SUSY scenario every known fermi (possessing a half-integral spin) particle such as quarks would have a boson counterpart, and every known boson (integral-spin) such as photons would have fermi counterparts. Pospelov argues that charged SUSY particles long-lived enough (more than a thousand seconds) to survive into the BBN era would bind with light nuclei and enhance (by a factor as large as 10^8) the buildup to heavier nuclei before the SUSY particle itself would decay. Pospelov says that his theory should be testable at the Large Hadron Collider (LHC) now under construction in Geneva. (Physical Review Letters, upcoming article