972 research outputs found
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
Extension of the Schiff theorem to ions and molecules
According to the Schiff theorem the nuclear electric dipole moment (EDM) is
screened in neutral atoms. In ions this screening is incomplete. We extend a
derivation of the Schiff theorem to ions and molecules. The finite nuclear size
effects are considered including Z^2 alpha^2 corrections to the nuclear Schiff
moment which are significant in all atoms and molecules of experimental
interest. We show that in majority of ionized atoms the nuclear EDM
contribution to the atomic EDM dominates while in molecules the contribution of
the Schiff moment dominates. We also consider the screening of electron EDM in
ions
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