We report scattering lengths for the 1 ⌺ g ϩ , 3 ⌺ u ϩ , and 5 ⌺ g ϩ adiabatic molecular potentials relevant to collisions of two metastable 2 3 S helium atoms as a function of the uncertainty in these potentials. These scattering lengths are used to calculate experimentally observable scattering lengths, elastic cross sections, and inelastic rates for any combination of states of the colliding atoms, at temperatures where the Wigner threshold approximation is valid.

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We report results for the Lorentzian profiles of the Li I, Na I and K I doublets and the Na I subordinate doublet broadened by helium perturbers for temperatures up to 3000 K. They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali-helium interaction. For all lines except the 769.9 nm K I line, the temperature dependence of the widths over the range 70 ≤ T ≤ 3000 K is accurately represented by the power law form w = aT b with 0.37 < b < 0.43. The 769.9 nm K I line has this form for 500 ≤ T ≤ 3000 K with b having the higher value of 0.49. Although the shifts have a more complex temperature dependence, they all have the general feature of increasing with temperature above T ∼ 500 K apart from the 769.9 K I line whose shift decreases with temperature.

Purely-long-range bound states of He(2s AbstractWe predict the presence and positions of purely-long-range bound states of 4 He(2s 3 S) + 4 He(2p 3 P ) near the 2s 3 S 1 + 2p 3 P 0,1 atomic limits. The results of the full multichannel and approximate models are compared, and we assess the sensitivity of the bound states to atomic parameters characterizing the potentials. Photoassociation to these purely-long-range molecular bound states may improve the knowledge of the scattering length associated with the collisions of two ultracold spin-polarized 4 He(2s 3 S) atoms, which is important for studies of Bose-Einstein condensates.

Abstract. We revisit the calculation of dark matter relic abundances in scalar-tensor gravity using a generic form A(ϕ * ) = e βϕ 2 * /2 for the coupling between the scalar field ϕ * and the metric, for which detailed Big Bang Nucleosynthesis constraints are available. We find that BBN constraints restrict the modified expansion rate in these models to be almost degenerate with the standard expansion history at the time of dark matter decoupling. In this case the maximum level of enhancement of the dark matter relic density was found to be a factor of ∼ 3, several orders of magnitude below that found in previous investigations.