  Recent measurements of the 4-point correlation function in large-scale galaxy
surveys have found apparent evidence of parity violation in the distribution of
galaxies. This cannot happen via dynamical gravitational effects in general
relativity. If such a violation arose from physics in the early Universe it
could indicate important new physics beyond the standard model, and would be at
odds with most models of inflation. It is therefore now timely to consider the
galaxy trispectrum in more detail. While the intrinsic 4-point correlation
function, or equivalently the trispectrum, its Fourier counterpart, is parity
invariant, the observed trispectrum must take redshift-space distortions into
account. Although the standard Newtonian correction also respects parity
invariance, we show that sub-leading relativistic corrections do not. We
demonstrate that these can be significant at intermediate linear scales and are
dominant over the Newtonian parity-invariant part around the equality scale and
above. Therefore when observing the galaxy 4-point correlation function, we
should expect to detect parity violation on large scales.
