We propose a model describing spin-half quantum particles in curved spacetime
    in the framework of quantum field theory. Our model is based on embodying
    Einstein’s equivalence principle and general covariance in the definition of
    quantum-particle states. With this model at hand, we compute several
    observables which characterise spin-half quantum particles in a gravitational
    field. In particular, we find that spin may precess in curved spacetime, even
    in the absence of torsion. This effect appears to be complementary to free-fall
    non-universality we have recently reported about for spinless quantum
    particles. Furthermore, we find that quantum-particle gravitational-potential
    energy is insensitive to wave-packet spreading in the Earth’s gravitational
    field, that is responsible for the non-universality of free fall in quantum
    theory. This theoretical result provides another channel for the experimental
    study of our quantum-particle model by using gravitational spectrometers.
    Finally, we also find that (elementary) fermions and antifermions are
    indistinguishable in gravity.

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