出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Recent spectroscopic observations of metal poor stars have indicated that both 7Li and 6Li have
abundance plateaus with respect to the metallicity. Abundances of 7Li are about a factor three
lower than the primordial abundance predicted by standard big-bang nucleosynthesis (SBBN),
and 6Li abundances are
120 of 7Li, whereas SBBN predicts negligible amounts of 6Li compared
to the detected level. These discrepancies suggest that 6Li has another cosmological or
Galactic origin than the SBBN. Furthermore, it could appear that 7Li (and also 6Li) has been
depleted from its primordial abundance by some post-BBN processes. We study the possibility
that the radiative decay of long-lived particles has affected the cosmological lithium abundances.
We calculate the non-thermal nucleosynthesis associated with the radiative decay, and explore the
allowed region of the parameters specifying the properties of long-lived particles. We also impose
constraints from observations of the CMB energy spectrum. It is found that non-thermal nucleosynthesis
produces 6Li at the level detected in metal poor halo stars (MPHSs), when the lifetime
of the unstable particles is of the order
108
1012 s and their initial abundance with respect
to that of the photons is
10
13
10
12 GeV
Eg 0, where Eg 0 is the emitted photon energy in
the radiative decay. We conclude that a combination of two different processes could explain the
lithium isotopic abundances in MPHSs. First, a non-thermal cosmological nucleosynthesis associated
with the radiative decay of unstable particles; and second, about the same degree of stellar
depletion of both primordial lithium isotopic abundances. If MPHSs experience 6Li depletion of
factor much greater than
3, the simple radiative decay process can not be the cause of large 6Li
abundances in MPHSs.
