Proper acceleration is a frame-invariant scalar representing the physical acceleration felt by an object, whereas coordinate acceleration depends on the choice of reference frame and coordinate system. No citation is needed for this foundational principle of kinematics and relativity.
The claim states a foundational, textbook definition from classical mechanics and the theory of relativity regarding proper versus coordinate acceleration. Because this is a matter of basic kinematic definitions and standard physics principles directly observable and definable by the structure of spacetime coordinates, it falls under common knowledge. None of the retrieved papers specifically target or debate this exact pedagogical distinction as their main thesis (they deal with general relativity, fluid simulations, and quantum fields), meaning no specialized citation is required.