We prove an
-regularity theorem
for vector-valued
-harmonic
maps, which are critical with respect to a partially free boundary condition, namely
that they map the boundary into a round sphere.
This does not seem to follow from the reflection method that
Scheven used for harmonic maps with free boundary (i.e., the case
):
the reflected equation can be interpreted as a
-harmonic
map equation into a manifold, but the regularity theory for such equations is only
known for round targets.
Instead, we follow the spirit of Schikorra’s recent work on free
boundary harmonic maps and choose a good frame directly at the free
boundary. This leads to growth estimates, which, in the critical regime
,
imply Hölder regularity of solutions. In the supercritical regime,
, we
combine the growth estimate with the geometric reflection argument: the reflected
equation is supercritical, but, under the assumption of growth estimates, solutions
are regular.
In the case
, for
stationary
-harmonic
maps with free boundary, as a consequence of a monotonicity formula
we obtain partial regularity up to the boundary away from a set of
-dimensional
Hausdorff measure.