Thursday, July 16, 2009

Primordial Lithium Problem

A Bitter Pill: The Primordial Lithium Problem Worsens
The lithium problem arises from the significant discrepancy between the primordial 7Li abundance as predicted by BBN theory and the WMAP baryon density, and the pre-Galactic lithium abundance inferred from observations of metal-poor (Population II) stars. This problem has loomed for the past decade, with a persistent discrepancy of a factor of 2--3 in 7Li/H.

Effect of quark-mass variation on big bang nucleosynthesis
Measurements of the primordial baryon-to-photon ratio
η from the cosmic microwave background from
WMAP [1], coupled with precise measurements of the
neutron half-life [2], have made big bang nucleosynthesis
(BBN) an essentially parameter-free theory [2, 3, 4]. In
this paradigm excellent agreement has been obtained between
predicted and observed abundances of deuterium
and 4He (see, e.g. the Particle Data Group review [2] and
references therin). However there is some disagreement
for 7Li, the only other element for which the abundance
has been measured to an accuracy at which fruitful comparison
with theory can be made. While the “lithium
problem” has been known for some time, it has been exacerbated
by recent measurements of the 3He(α, γ)7Be
reaction [5]. Standard BBN theory with η provided
by WMAP 5 overproduces 7Li by a factor of 2.4 – 4.3
(around 4 – 5σ) [4].

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