Local foliations by critical surfaces of the Hawking energy and small sphere limit


 Local foliations of area constrained Willmore surfaces on a 3-dimensional Riemannian manifold were constructed by Lamm, Metzger and Schulze, and Ikoma, Machiodi and Mondino. The leaves of these foliations are, in particular, critical surfaces of the Hawking energy in case they are contained in a totally geodesic spacelike hypersurface. We generalize these foliations to the general case of a non-totally geodesic spacelike hypersurface, constructing a unique local foliation of area constrained critical surfaces of the Hawking energy. A discrepancy when evaluating the so called small sphere limit of the Hawking energy was found by Friedrich. He studied concentrations of area constrained critical surfaces of the Hawking energy and obtained a result that apparently diﬀers from the well established small sphere limit of the Hawking energy of Horowitz and Schmidt, this small sphere limit in principle must be satisﬁed by any quasi local energy. We conﬁrm independently the discrepancy and explain the reasons for it to happen. We also prove that these surfaces are suitable to evaluate the Hawking energy in the sense of Lamm, Metzger and Schulze, and we ﬁnd an indication that these surfaces may induce an excess in the energy measured.