Mixmaster spacetime, Geroch’s transformation, and constants of motion

We show that for U(1)-symmetric spacetimes on S³×R a constant of motion associated with the well known Geroch transformation, a functional K[h_ij,π^ij], quadratic in gravitational momenta, is strictly positive in an open subset of the set of all U(1)-symmetric initial data, and therefore not weakly zero. The mixmaster initial data appear to be on the boundary of that set. We calculate the constant of motion perturbatively for the mixmaster spacetime and find it to be proportional to the minisuperspace Hamiltonian to the first order in the Misner anisotropy variables, i.e., weakly zero. Assuming that K is exactly zero for the mixmaster spacetime, we show that Geroch’s transformation, when applied to the mixmaster spacetime, gives a new U(1)-symmetric solution of the vacuum Einstein equations, globally defined on S²×S¹×R, which is nonhomogeneous and presumably exhibits mixmasterlike complicated dynamical behavior.