  Stellar streams are sensitive tracers of the gravitational potential, which
is typically assumed to be static in the inner Galaxy. However, massive mergers
like Gaia-Sausage-Enceladus can impart torques on the stellar disk of the Milky
Way that result in the disk tilting at rates of up to 10-20 deg/Gyr. Here, we
demonstrate the effects of disk tilting on the morphology and kinematics of
stellar streams. Through a series of numerical experiments, we find that
streams with nearby apocenters $(r_{\rm apo} \lesssim 20~\rm{kpc})$ are
sensitive to disk tilting, with the primary effect being changes to the
stream's on-sky track and width. Interestingly, disk tilting can produce both
more diffuse streams and more narrow streams, depending on the orbital
inclination of the progenitor and the direction in which the disk is tilting.
Our model of Pal 5's tidal tails for a tilting rate of 15 deg/Gyr is in
excellent agreement with the observed stream's track and width, and reproduces
the extreme narrowing of the trailing tail. We also find that failure to
account for a tilting disk can bias constraints on shape parameters of the
Milky Way's local dark matter distribution at the level of 5-10%, with the
direction of the bias changing for different streams. Disk tilting could
therefore explain discrepancies in the Milky Way's dark matter halo shape
inferred using different streams.
