Mashhoon effect

In physics, the Mashhoon effect describes the coupling of the intrinsic spin of a particle with the angular velocity of a rotating observer. The effect is named after Iranian-American physicist Bahram Mashhoon, who first formulated its existence in 1988.

The effect considers quantum mechanics in a rotating frame of reference, which leads to a coupling of intrinsic spin with the angular velocity of the rotation of a measuring device. In interferometry, the intrinsic spin-rotation coupling leads to a phase shift that is generally smaller than the Sagnac phase shift, which is due to the coupling of the orbital angular momentum of the particle with the rotation of the interferometer. The intrinsic spin-rotation coupling is independent of the inertial mass of the particle and originates from the tendency of intrinsic spin to keep its direction with respect to a background inertial frame ("inertia of intrinsic spin"). From the standpoint of observers that are spatially at rest in the rotating frame, the intrinsic spin therefore precesses in the opposite sense to the rotation of the frame.

Physical states in quantum mechanics are described by mass and spin, which characterize the irreducible unitary representations of the inhomogeneous Lorentz group. The inertial properties of a particle are determined by its inertial mass as well as spin. Phenomena associated with the spin-rotation coupling reveal the inertial properties of intrinsic spin.