Aharonov-Bohm effect in a draining bathtub vortex

We study planar waves in a circulating, draining fluid flow, which: (i) exhibit an analogue of the Aharonov-Bohm (AB) effect in Quantum Mechanics; (ii) obey a Klein-Gordon equation on an 'effective spacetime' which resembles the Kerr spacetime of General Relativity; and (iii) may be observed in the laboratory using gravity waves in a shallow basin. We describe a modified AB effect which depends on two dimensionless parameters, associated with the circulation a and draining beta rates; we call this the 'alpha beta effect'. We show that the alpha beta effect is inherently asymmetric even in the low-frequency limit, and that it leads to novel interference patterns which carry the signature of both rotation and absorption. (C) 2011 Elsevier B.V. All rights reserved.