Ehrenfest relations for ultrasound absorption in Sr2RuO4

We examine the Ehrenfest relations for the elastic constants of the spin-triplet superconducting state in Sr2RuO4. It is shown on a phenomenological level that the relations for different sound modes are not independent. This result may be used to analyze experimental data of sound velocity renormalization in the superconducting state. Finally, the relation between couplings of the order parameter and uniaxial strain is discussed from a microscopic point of view for the particular band structure of Sr2RuO4.