Speed of sound of a spin balanced Fermi gas with s- and d-wave pairings across the BCS-BEC evolution

The authors of a recent paper (PRA \textbf{87}, 013613 (2013)) argued that in fermionic systems with d-wave pairing the speed of sound is nonanalytic across the BCS-BEC crossover at the point where the chemical potential vanishes, regardless of the specific details of the interaction potential. On the contrary, the numerical results reported here suggest that the speed of sound across the BCS-BEC evolution of atomic Fermi gases with s- and d-wave pairings in two-dimensional square lattices is a smooth analytic function at the vanishing chemical potential.

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