Michael Sammon with Harsh Mathur
Axion Electrodynamics
Axions were introduced in particle physics in the 1970s to explain CP violation in the standard model. Subsequently axions have become a leading candidate for dark matter in Cosmology. The axion field has an unusual coupling to electromagnetism leading to remarkable electromagnetic phenomena that are the basis of experiments that aim to detect axions. Witten showed that if a charge is brought near an axion domain wall it produces an image, much like the electrostatic image of a charge brought near a conducting surface, but with the twist that the image in the axion domain wall is a magnetic monopole . Fundamental axions remain to be observed but in a remarkable development topological insulators have been discovered to have conducting surfaces that behave essentially like axion domain walls. Thus topological insulators are expected to provide a realization of the Witten effect . In this project we undertake a theoretical study of the experimental feasibility of observing a dual of the Witten effect wherein current rather than charge is reflected in a topological insulating surface. In the second part of the project we will return to fundamental axion detectors that have recently been used to put bounds on chameleon models of modified gravity . We will explore whether a recently proposed electrostatic analogy allows for a design of similar but more sensitive experiments to constrain the chameleon.