Screening and finite size corrections to the octupole and Schiff moments

Parity (P) and time reversal (T) violating nuclear forces create P, T -odd moments in expansion of the nuclear electrostatic potential. We derive expression for the nuclear electric octupole field which includes the electron screening correction (similar to the screening term in the Schiff moment). Then we calculate the Z alpha corrections to the Schiff moment which appear due to the finite nuclear size. Such corrections are important in heavy atoms with nuclear charge Z > 50. The Schiff and octupole moments induce atomic electric dipole moments (EDM) and P, T -odd interactions in molecules which are measured in numerous experiments to test CP-violation theories

Quasielastic neutron scattering from two dimensional antiferromagnets at a finite temperature

We consider frequency dependence of the neutron scattering amplitude from a two-dimensional quantum antiferromagnet. It is well known that the long range order disappears at any finite temperature and hence the elastic neutron scattering Bragg peak is transformed to the quasielastic neutron scattering spectrum ~dw/w. We show that the widely known formula for the spectrum of an isotropic antiferromagnet derived by Auerbach and Arovas should be supplemented by a logarithmic term that changes the integrated intensity by two times. A similar formula for an easy-plane magnet is very much different because of the Berezinsky-Kosterlitz-Thouless physics. An external uniform magnetic field switches smoothly the isotropic magnet to the easy-plane magnet. We demonstrate that the quasielastic neutron scattering spectrum in the crossover regime combines properties of both limiting cases. We also consider a quantum antiferromagnet close to the O(3) quantum critical point and show that in an external uniform magnetic field the intensity of elastic (quasielastic) neutron scattering peak depends linearly and significantly on the applied field.Comment: 9 pages, 4 figure