Lithium-6: A probe of the early universe

I consider the synthesis of 6Li due to the decay of relic particles, such as gravitinos or moduli, after the epoch of big bang nucleosynthesis. The synthesized 6Li/H ratio may be compared to 6Li/H in metal-poor stars which, in the absence of stellar depletion of 6Li, yields significantly stronger constraints on relic particle densities than the usual consideration of overproduction of 3He. Production of 6Li during such an era of nonthermal nucleosynthesis may also be regarded as a possible explanation for the relatively high 6Li/H ratios observed in metal-poor halo stars.     

Constraining antimatter domains in the early universe with big bang nucleosynthesis

We consider the effect of a small-scale matter-antimatter domain structure on big bang nucleosynthesis and place upper limits on the amount of antimatter in the early universe. For small domains, which annihilate before nucleosynthesis, this limit comes from underproduction of 4He. For larger domains, the limit comes from 3He overproduction. Since most of the 3He from &pmacr; 4He annihilation are themselves annihilated, the main source of primordial 3He is the photodisintegration of 4He by the electromagnetic cascades initiated by the annihilation.     

Superweakly interacting massive particles

We investigate a new class of dark matter: superweakly interacting massive particles (super-WIMPs). As with conventional WIMPs, super-WIMPs appear in well motivated particle theories with naturally the correct relic density. In contrast to WIMPs, however, super-WIMPs are impossible to detect in all conventional dark matter searches. We consider the concrete examples of gravitino and graviton cold dark matter in models with supersymmetry and universal extra dimensions, respectively, and show that super-WIMP dark matter satisfies stringent constraints from big bang nucleosynthesis and the cosmic microwave background.     

Astrophysical constraints on superlight gravitinos

I review the constraints on the mass of gravitinos that follow from considerations on energy loss in stars and from big bang nucleosynthesis arguments.     

The neutralinos of theSU(N,1) minimal supergravity model and standard cosmology

We discuss the effect of the lightest supersymmetric particle (LSP), a Higgsino, and of the gravitino of theSU(N,1) minimal SUGRA model in the standard big bang theory. The freeze out of the LSP depends on the gravitino mass and on the top mass and leads to restrictive lower bounds for these parameters in the model. The decay of a gravitino with mass in the few TeV range leads to a delay in the cooling of the universe before nucleosynthesis. This constitutes the main bound on the gravitino mass of the model. The results are compared with the more standard “simultaneous decay approximation”.     

Phase transitions and magnetic monopoles in SO(10)

In a unified gauge theory based on SO(10), the combination of a strongly first order phase transition and a magnetic confinement mechanism can suppress the density of magnetic monopoles at the time of nucleosynthesis. However, this only occurs if SO(10) breaks down to SU(3)_c ? U (1)_em via SU(4)_c ? [SU(2)_L × SU(2)_R]. For the other symmetry breaking patterns of SO(10) obtained with a minimal Higgs system, the potential conflict with the standard big bang cosmology is not naturally avoided.     

CBBN in the CMSSM

Catalyzed big bang nucleosynthesis (CBBN) can lead to overproduction of ⁶Li in gravitino dark matter scenarios in which the lighter stau is the lightest standard model superpartner. Based on a treatment using the state-of-the-art result for the catalyzed ⁶Li production cross section, we update the resulting constraint within the framework of the constrained minimal supersymmetric standard model (CMSSM). We confront our numerical findings with recently derived limits on the gaugino mass parameter m_1/2 and the reheating temperature T_R. PACS  12.60.Jv; 95.35.+d     

Cosmological limits to the number of massive leptons

If massive leptons exist, their associated neutrinos would have been copiously produced in the early stages of the hot, big bang cosmology. These neutrinos would have contributed to the total energy density and would have had the effect of speeding up the expansion of the universe. The effect of the speed-up on primordial nucleosynthesis is to produce a higher abundance of ⁴He. It is shown that observational limits to the primordial abundance of ⁴He lead to the constraint that the total number of types of heavy lepton must be less than or equal to 5.     

Study of the primordial lithium abundance

Lithium isotopes have attracted an intense interest because the abundance of both 6Li and 6Li from big bang nucleosynthesis (BBN) is one of the puzzles in nuclear astrophysics. Many investigations of both astrophysical observation and nucleosynthesis calculation have been carried out to solve the puzzle, but it is not solved yet. Several nuclear reactions involving lithium have been indirectly measured at China Institute of Atomic Energy, Beijing. The Standard BBN (SBBN) network calculations are then perfo...     

Entropy, neutrino physics, and the lithium problem: Why are there stars with essentially no lithium due to serious lithium deficiency in certain spatial regions in the early universe?

The consequence of abnormally low lithium abundance in a nearby population II star (which is almost as old as the supposed population III stars) as represented by HE0107-5240 is that the standard BBN theory is out of sync with observations. The analysis of the big bang nucleosynthesis may help explain the anomalously low value of lithium abundance in the star HE0107-5240, which by orthodox BBN, should not exist, as explained by Shigeyama et al. (2003) [1].     

Vacuum sampling in the landscape during inflation

We consider the phenomenological consequences of sampling multiple vacua during inflation motivated by an enormous landscape. A generic consequence of this sampling is the formation of domain walls, characterized by the scale mu of the barriers that partition the accessed vacua. We find that the success of big bang nucleosynthesis (BBN) implies mu > or = 10 TeV, as long as the sampled vacua have a nondegeneracy larger than O(MeV4). Otherwise, the walls will dominate and eventually form black holes that must reheat the universe sufficiently for BBN to take place; in this case, we obtain mu > or = 10(-5)MP. These black holes are not allowed to survive and contribute to cosmic dark matter density.     

Nuclear clustering aspects in astrophysics

Atomic nuclear clusters play a crucial role in nucleosynthesis in the universe, especially in the main sequence of heavy element synthesis. Cluster aspects in nucleosynthesis are briefly discussed based on a Cluster-Nucleosynthesis Diagram proposed here. Two recent topics on critical α-induced thermonuclear reactions are reviewed; the first one is the¹²C(α, γ)¹⁶O reaction for the He burning stage and the other one is the⁶ Li(α, n) ¹¹B reaction for the big bang nucleosynthesis. A new field of nuclear astrophysics using radioactive nuclear beams is also discussed.     

Explosive processes in nucleosynthesis

There are many explosive processes in nucleosynthesis: big bang nucleosynthesis, the rp-process, the γ-process, the ν-process, and the r-process. However, I will discuss just the rp-process and the r-process in detail, primarily because both seem to have been very active research areas of late, and because they have great potential for studies with radioactive nuclear beams. I will also discuss briefly the γ-process because of its inevitability in conjunction with the rp-process. Received: 1 May 2001 / Accepted: 4 December 2001     

Study of the primordial lithium abundance

Lithium isotopes have attracted an intense interest because the abundance of both ⁶Li and ⁷Li from big bang nucleosynthesis (BBN) is one of the puzzles in nuclear astrophysics. Many investigations of both astrophysical observation and nucleosynthesis calculation have been carried out to solve the puzzle, but it is not solved yet. Several nuclear reactions involving lithium have been indirectly measured at China Institute of Atomic Energy, Beijing. The Standard BBN (SBBN) network calculations are then performed to investigate the primordial Lithium abundance. The result shows that these nuclear reactions have minimal effect on the SBBN abundances of ⁶Li and ⁷Li.     

Bounds on the neutrino mass from the dark matter in the universe

Summary The problem of the missing matter in the Universe is reviewed and discussed in terms of massive neutrinos. The primordial abundances of light elements produced during the big bang nucleosynthesis can be used to determine firm bounds on the number of neutrino flavours and on the ratio of baryon to photon densities in the Universe. These limits imply that nonbaryonic matter is the dominant constituent of large-scale cosmic structures, being massive neutrinos the best guess for such a matter. In order that the Universe be closed, a value of the neutrino rest mass is derived, which agrees with the bounds obtained from the dynamics of galaxies and clusters of galaxies. It is also shown that density perturbations can hardly grow in a nucleon-dominated Universe, and massive neutrinos may be the seed for nucleon condensations. All these astrophysical and cosmological considerations suggest a lower and an upper bound of the neutrino rest mass. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.     

Signatures of a hidden cosmic microwave background

If there is a light Abelian gauge boson gamma' in the hidden sector its kinetic mixing with the photon can produce a hidden cosmic microwave background (HCMB). For meV masses, resonant oscillations gamma<-->gamma' happen after big bang nucleosynthesis (BBN) but before CMB decoupling, increasing the effective number of neutrinos Nnu(eff) and the baryon to photon ratio, and distorting the CMB blackbody spectrum. The agreement between BBN and CMB data provides new constraints. However, including Lyman-alpha data, Nnu(eff) > 3 is preferred. It is tempting to attribute this effect to the HCMB. The interesting parameter range will be tested in upcoming laboratory experiments.     

Cosmological constraints on bulk neutrinos

Recent models invoking extra space-like dimensions inhabited by (bulk) neutrinos are shown to have significant cosmological effects if the size of the largest extra dimension is R greater, similar 1 fm. We consider effects on cosmic microwave background anisotropies, big bang nucleosynthesis, deuterium and 6Li photoproduction, diffuse photon backgrounds, and structure formation. The resulting constraints can be stronger than either bulk graviton overproduction constraints or laboratory constraints.     

Dynamical Horizon Entropy Bound Conjecture in Loop Quantum Cosmology

The covariant entropy bound conjecture is an important hint for the quantum gravity, with several versions available in the literature. For cosmology, Ashtekar and Wilson-Ewing ever show the consistence between the loop gravity theory and one version of this conjecture. Recently, He and Zhang [J. High Energy Phys. 10 (2007) 077] proposed a version for the dynamical horizon of the universe, which validates the entropy bound conjecture for the cosmology filled with perfect fluid in the classical scenario when the universe is far away from the big bang singularity. However, their conjecture breaks down near big bang region. We examine this conjecture in the context of the loop quantum cosmology. With the example of photon gas, this conjecture is protected by the quantum geometry effects as expected.     

Dynamical Horizon Entropy Bound Conjecture in Loop Quantum Cosmology

The covariant entropy bound conjecture is an important hint for the quantum gravity, with several versions available in the literature. For cosmology, Ashtekar and Wilson-Ewing ever show the consistence between the loop gravity theory and one version of this conjecture. Recently, He and Zhang [J. High Energy Phys. 10 (2007) 077] proposed a version for the dynamical horizon of the universe, which validates the entropy bound conjecture for the cosmology filled with perfect fluid in the classical scenario when the universe is far away from the big bang singularity. However, their conjecture breaks down near big bang region. We examine this conjecture in the context of the loop quantum cosmology. With the example of photon gas, this conjecture is protected by the quantum geometry effects as expected.     

New constraints on “INO” masses from cosmology (I). Supersymmetric “inos”

In this first paper we derive new constraints on gravitino and photino masses in big bang cosmology. First, in the context of induced supersymmetry breaking we calculate explicitly the gravitino decay rate into gauginos, and find that in the absence of significant dilution the gravitino mass must be ?5 × 10⁴ GeV in order not to affect nucleosynthesis. We also find in this case that constraints in the lightest R-odd particle, the photino, differ significantly from earlier bounds based on analogy with stable heavy neutrino bounds in the standard model, due to out of equilibrium gravitino decay. In order to avoid both these constraints the gravitino distribution must be severely suppressed. If this is due to inflation, it must occur at a scale ?10¹⁰?10¹¹ GeV.