Axion Induced Oscillating Electric Dipole Moment of the Electron

TL;DR

This paper investigates how cosmic axions induce an oscillating electric dipole moment in electrons, analyzing the phenomenon theoretically and proposing potential experimental detection methods.

Contribution

It provides a detailed theoretical analysis of axion-induced electron EDM, including the effective action and decoupling limit, with implications for experimental detection.

Findings

Axion induces an oscillating electron EDM of ~10^{-32} e-cm.

The analysis includes local and nonlocal interaction contributions.

Potential experimental setups for detecting the signal are discussed.

Abstract

A cosmic axion, via the electromagnetic anomaly, induces an oscillating electric dipole for the electron of frequency $m_a$ and strength $\sim$(few)$\times 10^{-32}$ e-cm, two orders of magnitude above the nucleon, and within a few orders of magnitude of the present standard model constant limit. We give a detailed study of this phenomenon via the interaction of the cosmic axion, through the electromagnetic anomaly, with particular emphasis on the decoupling limit of the axion, $\partial_t a(t)\propto m_a \rightarrow 0$. The analysis is subtle, and we find the general form of the action involves a local contact interaction and a nonlocal contribution, analogous to the "transverse current" in QED, that enforces the decoupling limit. We carefully derive the effective action in the Pauli-Schroedinger non-relativistic formalism, and in Georgi's heavy quark formalism adapted to the "heavy electron" ($m_e>>m_a$). We compute the electric dipole radiation emitted by free electrons, magnets and currents, immersed in the cosmic axion field, and discuss experimental configurations that may yield a detectable signal.