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Collective P-and T-odd moments produced by parity and time invariance violating forces in reflection asymmetric nuclei are considered. The enhanced collective Schiff, electric dipole and octupole moments appear due to the mixing of rotational levels of opposite parity. These moments can exceed singleparticle moments by more than two orders of magnitude. The enhancement is due to the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. In turn these nuclear moments induce enhanced T-and P-odd effects in atoms and molecules. First a simple estimate is given and then a detailed theoretical treatment of the collective T-, P-odd electric moments in reflection asymmetric, odd-mass nuclei is presented and various corrections evaluated. Calculations are performed for octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac and Pa and the corresponding atoms. Experiments with such atoms may improve substantially the limits on time reversal violation.

The approach is developed for the description of isolated Fermi-systems with finite number of particles, such as complex atoms, nuclei, atomic clusters etc. It is based on statistical properties of chaotic excited states which are formed by the interaction between particles. New type of "microcanonical" partition function is introduced and expressed in terms of the average shape of eigenstates F (E k , E) where E is the total energy of the system. This partition function plays the same role as the canonical expression exp(−E (i) /T ) for open systems in thermal bath. The approach allows to calculate mean values and non-diagonal matrix elements of different operators. In particular, the following problems have been considered: distribution of occupation numbers and its relevance to the canonical and Fermi-Dirac distributions; criteria of equilibrium and thermalization; thermodynamical equation of state and the meaning of temperature, entropy and heat capacity, increase of effective temperature due to the interaction. The problems of spreading widths and shape of the eigenstates are also studied.

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The interaction between atoms behaves as −α/r n at large distances, and, owing to the large reduced mass µ of the collision pair, allows semiclassical treatment within the potential well. As a result, the low-energy scattering is governed by two large parameters: the asymptotic parameter γ = √ 2µα/h ≫ a (n−2)/2 0 (a 0 is the Bohr radius), and the semiclassical zero-energy phase Φ ≫ 1. In our previous work [Phys. Rev. A 48, 546 (1993)] we obtained an analytical expression for the scattering length a, which showed that it has 75% preference for positive values for n = 6, characteristic of collisions between ground-state neutral atoms. In this paper we calculate the effective range and show that it is a function of a, r e = F n − G n /a + H n /a 2 , where F n , G n and H n depend only on γ. Thus, we know the s phase shift at low momenta k ≪ γ −2/(n−2) from the expansion k cot δ 0 ≃ −1/a +

Abstract. We have applied many-body theory methods to study the interaction of low-energy positrons with noble-gas atoms. The positron-atom correlation potential includes explicitly the contribution from the target polarization by the positron and that from the virtual positronium (Ps) formation. It is demonstrated that the correlations and Ps formation (or tunnelling of electrons from the atom to the positron) create virtual levels in the positron-atom system. The existence of the virtual levels strongly influences the scattering and increases the positron annihilation rate by up to 400 times. The calculated elastic cross sections are in good agreement with experimental data. The inclusion of virtual Ps formation greatly improves the agreement with experimental annihilation rates with respect to calculations taking only the polarization into account. Our calculations have highlighted the difference between the calculation of positronatom scattering and the calculation of corresponding annihilation rates. The annihilation rate is very sensitive to the behaviour of the wavefunction at small positron-electron separations. A simple approximate formula based on the Sommerfeld factor is suggested to account for the effect of electron-positron Coulomb attraction on the annihilation rates.

We examine how the binding of light (A ≤ 8) nuclei depends on possible variations of hadronic masses, including meson, nucleon, and nucleon-resonance masses. Small variations in hadronic masses may have occurred over time; the present results can help evaluate the consequences for big bang nucleosynthesis. Larger variations may be relevant to current attempts to extrapolate properties of nucleon-nucleon interactions from lattice QCD calculations. Results are presented as derivatives of the energy with respect to the different masses so they can be combined with different predictions of the hadronic mass-dependence on the underlying current-quark mass m q .As an example, we employ a particular set of relations obtained from a study of hadron masses and sigma terms based on Dyson-Schwinger equations and a Poincaré-covariant Faddeev equation for confined quarks and diquarks. We find that nuclear binding decreases moderately rapidly as the quark mass increases, with the deuteron becoming unbound when the pion mass is increased by ∼60% (corresponding to an increase in X q = m q /Λ QCD of 2.5). In the other direction, the dineutron becomes bound if the pion mass is decreased by ∼15% (corresponding to a reduction of X q by ∼30%). If we interpret the disagreement between big bang nucleosynthesis calculations and measurements to be the result of variation in X q , we obtain an estimate δX q /X q = K·(0.013±0.002) where K ∼ 1 (the expected accuracy in K is about a factor of 2). The result is dominated by 7 Li data.

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