  We present a simple diagnostic that can be used to constrain the location of
the differential rotation in red giants with measured mixed mode rotational
splittings. Specifically, in red giants with radii $\sim 4R_\odot$, the
splittings of p-dominated modes (sound wave dominated) relative to those of
g-dominated modes (internal gravity wave dominated) are sensitive to how much
of the differential rotation resides in the outer convection zone versus the
radiative interior of the red giant. An independently measured surface rotation
rate significantly aids breaking degeneracies in interpreting the measured
splittings. We apply our results to existing observations of red giants,
particularly those of Kepler-56, and find that most of the differential
rotation resides in the radiative region rather than in the convection zone.
This conclusion is consistent with results in the literature from rotational
inversions, but our results are insensitive to some of the uncertainties in the
inversion process and can be readily applied to large samples of red giants
with even a modest number of measured rotational splittings. We argue that
differential rotation in the radiative interior strongly suggests that angular
momentum transport in red giants is dominated by local fluid instabilities
rather than large-scale magnetic stresses.

Solar and Stellar Astrophysics