Atomic CP-violating polarizability

TL;DR

This paper estimates the CP-violating polarizability in rare-gas atoms, relating it to the electron EDM and CP-odd interactions, and assesses the potential for experimental bounds on electron EDM via liquid xenon magnetization.

Contribution

It provides the first detailed theoretical estimates of atomic CP-violating polarizability for rare gases and explores experimental feasibility for constraining electron EDM.

Findings

BetaCP scales as Z^5 with nuclear charge Z.

Relativistic effects significantly enhance CP-violating polarizability.

Current experimental sensitivity is insufficient for competitive electron EDM bounds.

Abstract

Searches for CP violating effects in atoms and molecules provide important constrains on competing extensions to the standard model of elementary particles. In particular, CP violation in an atom leads to the CP-odd (T,P-odd) polarizability $\beta^\mathrm{CP}$: a magnetic moment $\mu^\mathrm{CP}$ is induced by an electric field $\mathcal{E}_0$ applied to an atom, $\mu^\mathrm{CP} = \beta^\mathrm{CP} \mathcal{E}_0 $. We estimate the CP-violating polarizability for rare-gas (diamagnetic) atoms He through Rn. We relate betaCP to the permanent electric dipole moment (EDM) of the electron and to the scalar constant of the CP-odd electron-nucleus interaction. The analysis is carried out using the third-order perturbation theory and the Dirac-Hartree-Fock formalism. We find that, as a function of nuclear charge Z, betaCP scales steeply as Z^5 R(Z), where slowly-varying R(Z) is a relativistic enhancement factor. Finally, we evaluate a feasibility of setting a limit on electron EDM by measuring CP-violating magnetization of liquid Xe. We find that such an experiment could provide competitive bounds on electron EDM only if the present level of experimental sensitivity to ultra-weak magnetic fields [Kominis et al., Nature 422, 596 (2003)] is improved by several orders of magnitude.