Coupling of New Order-Parameter Collective Modes to Sound Waves in SuperfluidHe3

A recently observed second collective-mode peak in the sound absorption in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ is shown to arise from weak excitation of a known order-parameter mode with weak-coupling frequency $\omega =\left(\sqrt{\frac{8}{5}}\right)\Delta \mathrm{}\left(T\right)\mathrm{}$ due to particle-hole-symmetry-violating terms. The somewhat lower value of the observed frequency might be caused by strong-coupling effects or admixture of $l=3\mathrm{}$ pair fluctuations.