Ultrasound as a sensitive probe off-wave pairing fluctuations inA3

We calculate the effect of f-wave pairing fluctuations on the collective-mode spectrum of ${}_{}{}^3{}_{}{}^{}\mathit{A}$. Our main result is that the normal flapping mode ceases to be well defined below a temperature ${\mathrm{T}}_{\mathrm{nfl}}$, which is proportional to the (attractive) f-wave coupling constant ${\mathrm{g}}_3$. As one approaches ${\mathrm{T}}_{\mathrm{nfl}}$ from above, the normal-flapping–mode frequency tends rapidly to zero. The corresponding peak feature in the sound attenuation thus provides a sensitive probe of ${\mathrm{g}}_3$.