Probing Axionlike Particles and the Axiverse with Superconducting Radio-Frequency Cavities

Bogorad, Zachary (Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA) ; Hook, Anson (Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA) ; Kahn, Yonatan (Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637, USA) (University of Illinois Urbana-Champaign, Urbana, Illinois 61801, USA) ; Soreq, Yotam (Theoretical Physics Department, CERN, CH-1211 Geneva 23, Switzerland) (Department of Physics, Technion, Haifa 32000, Israel)

09 July 2019

Abstract: Axionlike particles (ALPs) with couplings to electromagnetism have long been postulated as extensions to the standard model. String theory predicts an “axiverse” of many light axions, some of which may make up the dark matter in the Universe and/or solve the strong CP problem. We propose a new experiment using superconducting radio-frequency (SRF) cavities which is sensitive to light ALPs independent of their contribution to the cosmic dark matter density. Off-shell ALPs will source cubic nonlinearities in Maxwell’s equations, such that if a SRF cavity is pumped at frequencies ω1 and ω2, in the presence of ALPs there will be power in modes with frequencies 2ω1±ω2. Our setup is similar in spirit to light-shining-through-walls experiments, but because the pump field itself effectively converts the ALP back to photons inside a single cavity, our sensitivity scales differently with the strength of the external fields, allowing for superior reach as compared to experiments like OSQAR while utilizing current technology. Furthermore, a well-defined program of increasing sensitivity has a guaranteed physics result: the first observation of the Euler-Heisenberg term of low-energy QED at energies below the electron mass. We discuss how the ALP contribution may be separated from the QED contribution by a suitable choice of pump modes and cavity geometry, and conclude by describing the ultimate sensitivity of our proposed program of experiments to ALPs.

Published in: Physical Review Letters 123 (2019)
Published by: APS
DOI: 10.1103/PhysRevLett.123.021801
License: CC-BY-4.0

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