  On the main sequence, low-mass and solar-like stars are observed to spin-down
over time, and magnetized stellar winds are thought to be predominantly
responsible for this significant angular momentum loss. Previous studies have
demonstrated that the wind torque can be predicted via formulations dependent
on stellar properties, such as magnetic field strength and geometry, stellar
radius and mass, wind mass-loss rate, and stellar rotation rate. Although these
stars are observed to experience surface differential rotation, torque
formulations so far have assumed solid-body rotation. Surface differential
rotation is expected to affect the rotation of the wind and thus the angular
momentum loss. To investigate how differential rotation affects the torque, we
use the PLUTO code to perform 2.5D magnetohydrodynamic, axisymmetric
simulations of stellar winds, using a colatitude-dependent surface differential
rotation profile that is solar-like (i.e., rotation is slower at the poles than
the equator). We demonstrate that the torque is determined by the average
rotation rate in the wind, so that the net torque is less than that predicted
by assuming solid-body rotation at the equatorial rate. The magnitude of the
effect is essentially proportional to the magnitude of the surface differential
rotation, for example, resulting in a torque for the Sun that is $\sim 20 \%$
smaller than predicted by the solid-body assumption. We derive and fit a
semi-analytic formulation that predicts the torque as a function of the
equatorial spin rate, magnitude of differential rotation, and wind
magnetization (depending on the dipolar magnetic field strength and mass-loss
rate, combined).
