The cosmological 7Li problem from a nuclear physics perspective

Abstract

The primordial abundance of 7 Li as predicted by Big Bang Nucleosynthesis (BBN) is more than a factor 2 larger than what has been observed in metal-poor halo stars. Herein, we analyze the possibility that this discrepancy originates from incorrect assumptions about the nuclear reaction cross sections relevant for BBN. To do this, we introduce an efficient method to calculate the changes in the 7 Li abundance produced by arbitrary (temperature dependent) modifications of the nuclear reaction rates. Then, considering that 7 Li is mainly produced from 7 Be via the electron capture process 7 Be + e − → 7 Li + ν e , we assess the impact of the various channels of 7 Be destruction. Differently from previous analysis, we consider the role of unknown resonances by using a complete formalism which takes into account the effect of Coulomb and centrifugal barrier penetration and that does not rely on the use of the narrow-resonance approximation. As a result of this, the possibility of a nuclear physics solution to the 7 Li problem is significantly suppressed. Given the present experimental and theoretical constraints, it is unlikely that the 7 Be + n destruction rate is underestimated by the 2.5 factor required to solve the problem. We exclude, moreover, that resonant destruction in the channels 7 Be + t and 7 Be + 3 He can explain the 7 Li puzzle. New unknown resonances in 7 Be + d and 7 Be + α could potentially produce significant effects. Recent experimental results have ruled out such a possibility for 7 Be + d. On the other hand, for the 7 Be + α channel very favorable conditions are required. The possible existence of a partially suitable resonant level in 11 C is studied in the framework of a coupled-channel model and the possibility of a direct measurement is considered.

Higher D or Li: probes of physics beyond the standard model

“…It is fair to say that all of them require some additional input beyond what we normal term as standard. This may involve additional turbulent features in diffusive models of stellar evolution (Korn et al 2006) or new resonant reactions (Cyburt & Pospelov 2009;Chakraborty et al 2011;Broggini et al 2012). However, several of the possible solution come with the price of an increased D/H abundance: photon cooling (Erken et al 2012;Kusakabe et al 2012), variable fundamental constants (Dmitriev et al 2004;Coc et al 2007;Berengut et al 2010) and particle decays during or after BBN (Jedamzik 2004;Kawasaki et al 2005;Feng et al 2004;Ellis et al 2005;Jedamzik et al 2006;Cyburt et al 2006;Kusakabe et al -14 -2007;Cumberbatch et al 2007;Kawasaki et al 2008;Pospelov et al 2008;Jittoh et al 2008;Jedamzik & Pospelov 2009;Kusakabe et al 2008Kusakabe et al , 2010Jedamzik 2008a,b;Bailly et al 2009;Pospelov & Pradler 2010a,b;Cyburt et al 2010;Jittoh et al 2010;Kawasaki & Kusakabe 2011) all tend to increase D/H while yielding a 7 Li abundance which matches the low metallicity Pop II abundance determinations.…”

“…Resolution of the 7 Li problem has involved many different approaches. These range from questioning the nuclear reaction rates used in BBN calculations (Coc et al 2004;Angulo et al 2005;Cyburt et al 2004;Boyd et al 2010), or considering additional resonance reactions (Cyburt & Pospelov 2009;Chakraborty et al 2011;Broggini et al 2012). The possibility that depletion plays a role has been discussed at length (Vauclair & Charbonnel 1998;Pinsonneault et al 1998Pinsonneault et al , 2002Richard, Michaud & Richer 2005;Korn et al 2006;García Peréz et al 2008).…”

The Impact of New d(p,γ)He3 Rates on Big Bang Nucleosynthesis

“…Clearly accurate measurement of nuclear cross sections are critical for obtaining accurate light element abundances. 1 It is quite unlikely [22][23][24][25] that the solution to the lithium problem resides in the underlying nuclear physics. The discrepancy may be a result of stellar depletion [26] and there is some evidence of a broken lithium plateau at very low metallicity [27].…”

Metastable charged sparticles and the cosmological7Li problem

“…But the BBN expectations for 7 Li/H based on the WMAP baryon density are higher than the observed abundances by factors of 2 − 4, amounting formally to a 4 − 5σ discrepancy; this is the cosmological lithium problem [52,53]. Nuclear uncertainties [53][54][55][56] and/or resonances are all but excluded as solutions to the problem [56][57][58][59][60][61]. There is the possibility that depletion plays a role in altering the 7 Li abundance [62].…”