Probing “Continuous Spin” QED with Rare Atomic Transitions

by Aidan Reilly

Wednesday 27 May 2026, 12:30 → 14:30 America/Los_Angeles

48/2-224 - Madrone (SLAC)

An intriguing and elementary possibility is that familiar massless particles like the photon could be “continuous spin'' particles (CSP) with a small but non-zero spin Casimir $\rho$. In this case, the familiar two polarization states of the photon are accompanied by an infinite tower of integer spaced helicity modes, with couplings dictated entirely by Lorentz symmetry and the parameter $\rho$.  We present a formalism for computing bound state atomic transitions when $\rho \neq 0$, employing path integral methods not often used for bound state computations, but that readily generalize to the CSP case.  We compute several illustrative amplitudes and show that, in addition to modifying known channels, $\rho \neq 0$ also opens new decay channels for atomic transitions with rates controlled by $\rho\alpha/\omega$ for transition frequency $\omega$. These corrections can appreciably modify atomic decay rates suggesting new directions for fundamental tests of QED in laboratory experiments. 

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