Low-temperature antihydrogen-atom scattering

A simple method to include the strong force in atom-antiatom scattering is presented. It is based on the strong-force scatteringn length between the nucleon and antinucleon. Using this method elastic and annihilation cross sections are calculated for hydrogen-antihydrogen and helium-antihydrogen scattering. The results are compared to first-order perturbation theory using a pseudo potential. The pseudo-potential approach works fairly well for hydrogen-antihydrogen scattering, but fails for helium-antihydrogen scattering where strong-force effects are more prominent.Comment: 9 pages, 2 figures, to be published in Nuclear Instruments and Methods

Simulations of Sisyphus cooling including multiple excited states

We extend the theory for laser cooling in a near-resonant optical lattice to include multiple excited hyperfine states. Simulations are performed treating the external degrees of freedom of the atom, i.e., position and momentum, classically, while the internal atomic states are treated quantum mechanically, allowing for arbitrary superpositions. Whereas theoretical treatments including only a single excited hyperfine state predict that the temperature should be a function of lattice depth only, except close to resonance, experiments have shown that the minimum temperature achieved depends also on the detuning from resonance of the lattice light. Our results resolve this discrepancy.Comment: 7 pages, 6 figure

The few-body problem for trapped bosons with large scattering length

We calculate energy levels of two and three bosons trapped in a harmonic oscillator potential with oscillator length $a_{\mathrm osc}$. The atoms are assumed to interact through a short-range potential with a scattering length $a$, and the short-distance behavior of the three-body wave function is characterized by a parameter $\theta$. For large positive $a/a_{\mathrm osc}$, the energies of states which, in the absence of the trap, correspond to three free atoms approach values independent of $a$ and $\theta$. For other states the $\theta$ dependence of the energy is strong, but the energy is independent of $a$ for $|a/a_{\mathrm osc}|\gg1$.Comment: 4 pages, 3 figure

A nonadiabatic semi-classical method for dynamics of atoms in optical lattices

We develop a semi-classical method to simulate the motion of atoms in a dissipative optical lattice. Our method treats the internal states of the atom quantum mechanically, including all nonadiabatic couplings, while position and momentum are treated as classical variables. We test our method in the one-dimensional case. Excellent agreement with fully quantum mechanical simulations is found. Our results are much more accurate than those of earlier semi-classical methods based on the adiabatic approximation.Comment: 7 pages, 5 figures, submitted to European Physical Journal

Experimental measurement of efficiency and transport coherence of a cold atom Brownian motor in optical lattices

The rectification of noise into directed movement or useful energy is utilized by many different systems. The peculiar nature of the energy source and conceptual differences between such Brownian motor systems makes a characterization of the performance far from straightforward. In this work, where the Brownian motor consists of atoms interacting with dissipative optical lattices, we adopt existing theory and present experimental measurements for both the efficiency and the transport coherence. We achieve up to 0.3% for the efficiency and 0.01 for the P\'eclet number

The role of antihydrogen formation in the radial transport of antiprotons in positron plasmas

Simulations of the behaviour of antiprotons in positron clouds during antihydrogen formation.The work added to our understanding of the underlying processes, including the dominant role played by antihydrogen formation itself

On the formation of trappable antihydrogen

Study, using extensive simulations, of the fraction of trappable antihydrogen under typical experimental conditions. Discovery that positron collisions can influence the magnetic moment of the antihydrogen after formation to promote the trappable fraction. Thus attempting experiments at higher positron densities should be beneficial

Final-State Spectrum of 3^3He after β−\beta^- Decay of Tritium Anions T−^-

The final-state spectrum of $\beta$ decaying tritium anions T$^-$ was calculated. The wavefunctions describing the initial T$^-$ ground state and the final $^3$He states were obtained by the full configuration-interaction method. The transition probability was calculated within the sudden approximation. The transition probability into the electronic continuum is extracted from the complex-scaled resolvent and is shown to converge for very high-energies to an approximate analytical model probability distribution.Comment: 7 pages, 2 figure

Four-boson scale near a Feshbach resonance

We show that an independent four-body momentum scale $\mu_{(4)}$ drives the tetramer binding energy for fixed trimer energy (or three-body scale $\mu_{(3)}$) and large scattering length ($a$). The three- and four-body forces from the one-channel reduction of the atomic interaction near a Feshbach resonance disentangle $\mu_{(4)}$ and $\mu_{(3)}$. The four-body independent scale is also manifested through a family of Tjon-lines, with slope given by $\mu_{(4)}/\mu_{(3)}$ for $a^{-1}=0$. There is the possibility of a new renormalization group limit cycle due to the new scale

Modelling the evolution and nucleosynthesis of carbon-enhanced metal-poor stars

We present the results of binary population simulations of carbon-enhanced metal-poor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may instead require much more efficient dredge-up from low-metallicity asymptotic giant branch stars.Comment: 6 pages, 1 figure, to appear in the proceedings of IAU Symposium 252 "The Art of Modelling Stars in the 21st Century", April 6-11, 2008, Sanya, Chin