Metastable charged sparticles and the cosmological⁷Li problem

Abstract

We consider the effects of metastable charged sparticles on Big-Bang Nucleosynthesis (BBN), including bound-state reaction rates and chemical effects. We make a new analysis of the bound states of negatively-charged massive particles with the light nuclei most prominent in BBN, and present a new code to track their abundances, paying particular attention to that of 7 Li. Assuming, as an example, that the gravitino is the lightest supersymmetric particle (LSP), and that the lighter stau slepton,τ 1 , is the metastable next-to-lightest sparticle within the constrained minimal supersymmetric extension of the Standard Model (CMSSM), we analyze the possible effects on the standard BBN abundances ofτ 1 bound states and decays for representative values of the gravitino mass. Taking into account the constraint on the CMSSM parameter space imposed by the discovery of the Higgs boson at the LHC, we delineate regions in which the fit to the measured light-element abundances is as good as in standard BBN. We also identify regions of the CMSSM parameter space in which the bound state properties, chemistry and decays of metastable charged sparticles can solve the cosmological 7 Li problem.

Non-Gaussian error distribution of 7Li abundance measurements

“…See, for instance Jedamzik et al (2006), Coc et al (2007), Chakraborty et al (2011), Fields (2011), Erkem et al (2012, Cyburt et al (2012), Ouyed (2013), and Kusakabe & Kawasaki (2014).…”

Observational challenges for the standard FLRW model

“…One observational contradiction with ΛCDM that is widely accepted in the community is the primordial lithium abundance anomaly: the lack of 7 Li/H in metal-poor halo field stars in our Galaxy is inconsistent with the ΛCDM cosmic microwave background (CMB) expectation at about 5.3σ [4], unless new particles such as decaying gravitinos are assumed [5].…”

Gravitino decays and the cosmological lithium problem in light of the LHC Higgs and supersymmetry searches

“…Furthermore, until several such measurements confirm the precision of this value, we cannot be assured that no in situ destruction of D/H has taken place, given the dispersion in the extant data [24]. 3 He/D As discussed in [23], we expect the ratio 3 He/D [27] to be a monotonically increasing function of time, and therefore consider the solar ratio 3 He/D ≃ 1 [28] to be a conservative upper bound on the BBN ratio. As we see later, this constraint is satisfied comfortably within all the region of interest, so we do not include it in our global χ 2 function, and hence do not need to assign an uncertainty.…”

“…As we see later, this constraint is satisfied comfortably within all the region of interest, so we do not include it in our global χ 2 function, and hence do not need to assign an uncertainty. 4 He Following [23], we use the estimate [29] Y p = 0.2534 ± 0.0083 (2) based on an analysis of the regression of Y vs. O/H. This should be compared to the SBBN value of 0.2487 ± 0.0002.…”

“…In the subsequent figures, these ranges are left unshaded and coloured yellow, red and magenta, respectively. We now comment on the ranges of the light-element abundances that we consider to be preferred and use in the subsequent χ 2 analysis: more discussion can be found in [23] Strongly excluded < 0.5 − < 0.22 …”