Abstract: We point out that the existence of metastable, [tau] > 103 s, negatively charged electroweak-scale particles ([X.sup.-]) alters the predictions for lithium and other primordial elemental abundances for A > 4 via the formation of bound states with nuclei during Big-Bang nucleosynthesis (BBN). In particular, we show that the bound states of [X.sup.-] with helium, formed at temperatures of about T = [10.sup.8] K, lead to the catalytic enhancement of [sup.6]Li production, which is eight orders of magnitude more efficient than the standard channel. In particle physics models, where subsequent decay of [X.sup.-] does not lead to large nonthermal BBN effects, this directly translates to the level of sensitivity to the number density of longlived [X.sup.-] particles ([tau] > [10.sup.5] s) relative to entropy of [n.sub.X]- /s [??] 3 x [10.sup.-17], which is one of the most stringent probes of electroweak scale remnants known to date. It is also argued that unstable charged particles with lifetime of order ~2000 s may naturally lead to the depletion of [sup.7]Li by a factor of two, making it consistent with observationally determined abundances.
PACS No.: 98.80.Ft
Resume : Nous soulignons que l'existence de particules electro-faibles negativement chargees ([X.sup.-]) et metastables ([tau] > 103 s) modifie nos predictions pour la formation originale de lithium et d'autres elements avec A > 4, via la formation d'etats lies pendant la BBN. Nous montrons en particulier que la formation d'etats lies de [X.sup.-] avec de l'helium, formes a une temperature de T = [10.sup.8] K, mene a une augmentation catalytique de la production de [sup.6]Li qui est huit ordres de grandeur plus efficace que le modele standard. Dans les modeles de particules elementaires ou la desintegration subsequente de [X.sup.-] ne mene pas a des effets non thermiques importants de BBN, ceci se traduit directement en niveau de sensibilite sur le nombre de particules [X.sup.-] de longue vie ([tau] > [10.sup.5] s) relativement a l'entropie s, [n.sub.X]- /s [??] 3 x [10.sup.-17], qui est parmi les tests les plus severes connus du vestige de l'echelle electro-faible. Nous pouvons aussi dire que l'existence de particules chargees instables (~2000 s) menerait naturellement a une diminution par un facteur 2 du [sup.7]Li, ce qui correspond precisement a la situation observee.
[Traduit par la Redaction]
1. Introduction
This paper is based on two recentworks, [1, 2]. Standard BigBang nucleosynthesis (SBBN) is a well-established theory that makes predictions for elemental abundances of light elements, H, D, He, and Li, as functions of only one free parameter, the ratio of baryon-number to photon-number densities.Agreement of the observed abundances for D and [sup.4]He with the SBBN predictions that use an additional cosmic microwave background (CMB)-derived [3] input value of [n.sub.b]/s = 0.9 x [10.sup.-10] serves as a sensitive probe of New Physics.
Perhaps the most exciting prospect of studying the primordial abundances is the possibility of testing the combination of Standard Model and general relativity, which we call SBBN, or standard BBN. To this end, it is important to understand how the nonstandard physics can affect the outcome of nuclear reactions (see, for example, ref. 4 for a review). Schematically, the BBN equations can be represented as
d[Y.sub.i]/[d.sub.t] = -H(T) Td[Y.sub.i]/[d.sub.T] = [SIGMA]([[TAU].sub.ij][Y.sub.j] + [[TAU].sub.ikl][Y.sub.k][Y.sub.l] + ...)
Energy of reactants ~ T [??] MeV
H(T) = const x [N.sub.*.sup.1/2] [T.sup.2]/[M.sub.Pl]
where [N.sub.*] = [N.sub.boson] + 7/8 [N.sub.fermion] (1)
In this formula, Yi are the abundances of light elements, [[TAU].sub.ij] ... are the generalized (positive or negative) rates for creation or destruction of element i with participation of j, k ..., H(T) is the Hubble expansion rate, [M.sub.Pl] is the Planck constant, and [N.sub.*] is the number of effective degrees of freedom comprisng fermionic and bosonic fields. …
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