Ref HAL: hal-00398313_v1
Ref Arxiv: 0906.2087
DOI: 10.1088/1367-2630/11/10/105028
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119 citations
Abstract:

We review how our current understanding of the light element synthesis duringthe Big Bang Nucleosynthesis era may help shed light on the identity ofparticle dark matter.

Comments: Part of Focus on Dark Matter and Particle Physics. 20 pp.

Ref HAL: hal-00378193_v1
Ref Arxiv: 0903.3974
DOI: 10.1088/1126-6708/2009/05/103
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39 citations
Abstract:

We re-consider the gravitino as dark matter in the framework of theConstrained MSSM. We include several recently suggested improvements on: (i)the thermal production of gravitinos, (ii) the calculation of the hadronicspectrum from NLSP decay and (iii) the BBN calculation including staubound-state effects. In most cases we find an upper bound on the reheatingtemperature $\treh\lsim {\rm a few}\times 10^7\gev$ from over-production of$^6{\rm Li}$ from bound state effects. We also find an upper limit on the staulifetime of $3\times10^4 \sec$, which is nearly an order of magnitude largerthan the simple limit $5\times 10^3 \sec$ often used to avoid the effect ofbound-state catalysis. The bound on $\treh$ is relaxed to $\lsim {\rm afew}\times 10^8\gev$ when we use a more conservative bound on ${^6}{\rmLi}/{^7}{\rm Li}$, in which case a new region at small stau mass at $\sim100\gev$ and much longer lifetimes opens up. Such a low stau mass region can beeasily tested at the LHC.

Ref HAL: hal-00344952_v1
Ref Arxiv: 0812.0788
DOI: 10.1103/PhysRevD.80.063509
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50 citations
Abstract:

Supersymmetric extensions of the standard model of particle physics assumingthe gravitino to be the lightest supersymmetric particle (LSP), and with thenext-to-LSP decaying to the gravitino during Big Bang nucleosynthesis, areanalyzed. Particular emphasis is laid on their potential to solve the "Li7problem", an apparent factor 2-4 overproduction of Li7 in standard Big Bangnucleosynthesis (BBN), their production of cosmologically important amounts ofLi6, as well as the resulting minimum gravitino dark matter densities in thesemodels. The study includes several improvements compared to prior studies.Heavy gravitinos in the constrained minimal supersymmetric standard model(CMMSM) are reanalyzed, whereas light gravitinos in gauge-mediatedsupersymmetry breaking scenarios (GMSB) are studied for the first time. It isconfirmed that decays of NLSP staus to heavy gravitinos, while producing allthe dark matter, may at the same time resolve the Li7 problem. For NLSP decaytimes ~ 1000 sec, such scenarios also lead to cosmologically important Li6 (andpossibly Be9) abundances. However, as such scenarios require heavy > 1 TeVstaus they are likely not testable at the LHC. It is found that decays of NLSPstaus to light gravitinos may lead to significant Li6 (and Be9) abundances,whereas NLSP neutralinos decaying into light gravitinos may solve the Li7problem. Though both scenarios are testable at the LHC they may not lead to theproduction of the bulk of the dark matter. A section of the paper outlinesparticle properties required to significantly reduce the Li7 abundance, and/orenhance the Li6 (and possibly Be9) abundances, by the decay of an arbitraryrelic particle.

Comments: 13 pages (revtex), 9 figures. publié, 10.1103/PhysRevD.80.063509

Ref HAL: hal-00281347_v1
Ref Arxiv: 0710.5153
DOI: 10.1088/1475-7516/2008/03/008
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57 citations
Abstract:

The Big Bang nucleosynthesis (BBN) process in the presence of charged massive particles (CHAMPs) is studied in detail. All currently known effects due to the existence of bound states between CHAMPs and nuclei, including possible late-time destruction of 6Li and 7Li, are included. The study sets conservative bounds on CHAMP abundances in the decay time range 3\times 10^2~\mathrm {s}\lesssim \tau_x\lesssim 10^{12}~\mathrm {s} . It is stressed that the production of 6Li at early times T~10 keV is overestimated by a factor ~10 when the approximation of the Saha equation for the 4He bound state fraction is utilized. To obtain conservative limits on the abundance of CHAMPs, a Monte Carlo analysis with ~3 × 106 independent BBN runs, varying the reaction rates of 19 different reactions, is performed. The analysis yields the surprising result that, except for small areas in the particle parameter space, conservative constraints on the abundance of decaying charged particles are currently very close to those of neutral particles. It is shown that, in the case that the rates of a number of heretofore unconsidered reactions may be determined reliably in the future, it is conceivable that the limit on CHAMPs in the early Universe could be tightened by orders of magnitude.

Ref HAL: hal-00288413_v1
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Abstract:

The epoch of Big Bang nucleosynthesis presents a precision observational test of cosmic conditions at cosmic temperatures below a few MeV. Comparison of theoretically predicted abundances of $^2$H, $^3$He, $^4$He, and $^7$Li with observationally inferred primordial abundances has led to the standard model of Big Bang nucleosythesis (SBBN). In this talk I review the observational determination of light-element abundances, with particular focus on $^7$Li and $^2$H. It is found that predicted $^7$Li production in SBBN is around a factor three higher than the observationally inferred abundance of this isotope. Astrophysical effects, as well as nuclear reaction rate uncertainties, which may or may not explain such a discrepancy are reviewed. Recent observations of $^6$Li abundances in low-metallicity halo stars have revealed a surprisingly high $^6$Li abundance in disaccord with expectations of $^6$Li production by galactic cosmic rays. I review the proposed astrophysical scenarios which may reproduce the data. In the second part of this talk, it is assumed that the $^6$Li and $^7$Li anomalies are signs of physics beyond the standard model of particle physics and BBN. The currently proposed modifications to BBN to account for these anomalies are reviewed. Particularly promising may be the possible existence of supersymmetry with the superpartner of the graviton, the gravitino, being the dark matter. In this case, the decay of either the superpartner of the U(1) hypercharge gauge boson, or the superpartner of the tau-lepton may decay during BBN, thereby solving both problems at once. The resulting cosmology, implications for the LHC, and the physics entering the BBN calculations are highlighted.

Ref HAL: in2p3-00182623_v1
Ref Arxiv: 0707.2070
DOI: 10.1103/PhysRevD.77.063524
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62 citations
Abstract:

Charged massive particles (CHAMPs), when present during the Big Bang nucleosynthesis (BBN) era, may significantly alter the synthesis of light elements when compared to a standard BBN scenario. This is due to the formation of bound states with nuclei. This paper presents a detailed numerical and analytical analysis of such CHAMP BBN. All reactions important for predicting light-element yields are calculated within the Born approximation. Three priorly neglected effects are treated in detail:(a) photodestruction of bound states due to electromagnetic cascades induced by the CHAMP decay, (b) late-time efficient destruction/production of H2, Li6, and Li7 due to reactions on charge Z=1 nuclei bound to CHAMPs, and (c) CHAMP exchange between nuclei. Each of these effects may induce orders-of-magnitude changes in the final abundance yields. The study focusses on the impact of CHAMPs on a possible simultaneous solution of the Li6 and Li7 problems. It is shown that a priorly suggested simultaneous solution of the Li6 and Li7 problems for a relic decaying at tau_x = 1000 sec is only very weakly dependent on the relic being neutral or charged, unless its hadronic branching ratio is Bh << 10^-4 very small. By use of a Monte-Carlo analysis it is shown that within CHAMP BBN the existence of further parameter space for a simultaneous solution of the Li6 and Li7 problem for long decay times tau_x > 10^6 sec seems possible but fairly unlikely.

Comments: 15 pages (revtex), 14 figures, large changes in analysis and conclusions

Ref HAL: hal-00288565_v1
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Abstract:

Cosmic dark matter may be in form of superweakly interacting elementary particles such as the gravitino or the axino. Direkt dark matter searches are not capable of discovering such dark matter. However, gravitinos and axinos are often produced as warm dark matter leaving a signature and the primordial power spectrum. Moreover, their production often entails a perturbation of the epoch of Big Bang nucleosynthesis, thus leaving a signature in the light element abundances. In this talk both of these potential signatures are discussed.