We revisit quantum-classical hybrid systems of the Sudarshan type under the light of Galilean covariance. We show that these kinds of hybrids cannot be given as a unitary representation of the Galilei group and at the same time conserve the total linear momentum unless the interaction term only depends on the relative canonical velocities.

• Received 12 June 2020
• Accepted 21 September 2020

DOI:https://doi.org/10.1103/PhysRevA.102.042221