  It is usually assumed that the angular momentum (AM) of dark matter halos
arises during the linear stages of structure formation, as a consequence of the
coupling between the proto-haloes' shape and the tidal field produced by their
surrounding density perturbations. This approach, known as linear tidal torque
theory (TTT), has been shown to make fairly good predictions about the mean
evolution of both the AM amplitude and orientation up to approximately the time
when the proto-haloes collapse. After this point, proto-haloes are increasingly
affected by non-linear processes that are not taken into account by the model.
However, it has been seen in numerical simulations that, even at very early
stages, the AM of proto-haloes is systematically reoriented towards
perpendicularity with respect to the forming cosmic filaments, in contradiction
with the fixed direction expected from the TTT. In this work we present a novel
analytical approach that introduces an anisotropic scaling factor to the
standard TTT equations, which allows the AM orientation to change in time, even
during the linear regime. The amplitude and direction of this shift depend on
the large scale tidal field around the forming proto-haloes. Our results
significantly improve the predictions for the AM direction up to the time of
protohalo collapse and, in some cases, even further in time.
