Inhomogeneous Big Bang Nucleosynthesis: Upper Limit on Omega_b and Production of Lithium, Beryllium, and Boron

We examine the Big Bang nucleosynthesis (BBN) process in the presence of small-scale baryon inhomogeneities. Primordial abundance yields for D, He4, Li6, Li7, Be9, and B11 are computed for wide ranges of parameters characterizing the inhomogeneities taking account of all relevant diffusive and hydrodynamic processes. These calculations may be of interest due to (a) recent observations of the anisotropies in the cosmic microwave background radiation favoring slightly larger baryonic contribution to the critical density, Omega_b, than allowed by a standard BBN scenario and (b) new observational determinations of Li6 and Be9 in metal-poor halo stars. We find considerable parameter space in which production of D and He4 is in agreement with observational constraints even for Omega_b h^2 a factor 2-3 larger than the Omega_b inferred from standard BBN. Nevertheless, in this parameter space synthesis of Li7 in excess of the inferred Li7 abundance on the Spite plateau results. Production of Li6, Be9, and B11 in inhomogeneous BBN scenarios is still typically well below the abundance of these isotopes observed in the most metal-poor stars to date thus neither confirming nor rejecting inhomogeneous BBN. In an appendix we summarize results of a reevaluation of baryon diffusion constants entering inhomogeneous BBN calculations.Comment: 11 pages, 4 figures, revtex, submitted to PR

Low Mach Number Modeling of Type Ia Supernovae

We introduce a low Mach number equation set for the large-scale numerical simulation of carbon-oxygen white dwarfs experiencing a thermonuclear deflagration. Since most of the interesting physics in a Type Ia supernova transpires at Mach numbers from 0.01 to 0.1, such an approach enables both a considerable increase in accuracy and savings in computer time compared with frequently used compressible codes. Our equation set is derived from the fully compressible equations using low Mach number asymptotics, but without any restriction on the size of perturbations in density or temperature. Comparisons with simulations that use the fully compressible equations validate the low Mach number model in regimes where both are applicable. Comparisons to simulations based on the more traditional anelastic approximation also demonstrate the agreement of these models in the regime for which the anelastic approximation is valid. For low Mach number flows with potentially finite amplitude variations in density and temperature, the low Mach number model overcomes the limitations of each of the more traditional models and can serve as the basis for an accurate and efficient simulation tool.Comment: Accepted for publication in the Astrophysical Journal 31 pages, 5 figures (some figures degraded in quality to conserve space

Systematics of heavy-ion fusion hindrance at extreme sub-barrier energies

The recent discovery of hindrance in heavy-ion induced fusion reactions at extreme sub-barrier energies represents a challenge for theoretical models. Previously, it has been shown that in medium-heavy systems, the onset of fusion hindrance depends strongly on the "stiffness" of the nuclei in the entrance channel. In this work, we explore its dependence on the total mass and the $Q$-value of the fusing systems and find that the fusion hindrance depends in a systematic way on the entrance channel properties over a wide range of systems.Comment: Submitted to Phys. Rev. Lett., 5 pages, 3 figure

Should heroin be prescribed to heroin misusers? Yes

Some heroin addicts are very difficult to treat. Jürgen Rehm and Benedikt Fischer believe that maintenance with heroin is the way forward for this group, but Neil McKeganey argues that it is treating the effects of misuse not the addictio

Extraction of nucleus-nucleus potential and energy dissipation from dynamical mean-field theory

Nucleus-nucleus interaction potentials in heavy-ion fusion reactions are extracted from the microscopic time-dependent Hartree-Fock theory. When the center-of-mass energy is much higher than the Coulomb barrier energy, extracted potentials identify with the frozen density approximation. As the center-of-mass energy decreases to the Coulomb barrier energy, potentials become energy dependent. This dependence indicates dynamical reorganization of internal degrees of freedom and leads to a reduction of the "apparent" barrier. Including this effect leads to the Coulomb barrier energy very close to experimental one. Aspects of one-body energy dissipation extracted from the mean-field theory are discussed.Comment: 6 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08: New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September 22-26, 2008, Chicago, US

Fusion at deep subbarrier energies: potential inversion revisited

For a single potential barrier, the barrier penetrability can be inverted based on the WKB approximation to yield the barrier thickness. We apply this method to heavy-ion fusion reactions at energies well below the Coulomb barrier and directly determine the inter-nucleus potential between the colliding nuclei. To this end, we assume that fusion cross sections at deep subbarrier energies are governed by the lowest barrier in the barrier distribution. The inverted inter-nucleus potentials for the $^{16}$O +$^{144}$Sm and $^{16}$O +$^{208}$Pb reactions show that they are much thicker than phenomenological potentials. We discuss a consequence of such thick potential by fitting the inverted potentials with the Bass function.Comment: 8 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08: New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September 22-26, 2008, Chicago, US

Exact Stochastic Mean-Field dynamics

The exact evolution of a system coupled to a complex environment can be described by a stochastic mean-field evolution of the reduced system density. The formalism developed in Ref. [D.Lacroix, Phys. Rev. E77, 041126 (2008)] is illustrated in the Caldeira-Leggett model where a harmonic oscillator is coupled to a bath of harmonic oscillators. Similar exact reformulation could be used to extend mean-field transport theories in Many-body systems and incorporate two-body correlations beyond the mean-field one. The connection between open quantum system and closed many-body problem is discussed.Comment: Proceedings series of Proceedings of "FUSION08: New Aspects of Heavy Ion Collisions near the Coulomb Barrier", September 22-26, 2008, Chicago, US