$K(2)$-local splittings of finite Galois extensions of $MU\langle6\rangle$ and $MString$

Abstract

Using a Milnor-Moore argument we show that, $K(2)$-locally at the prime $2$, the spectra $MU\langle 6\rangle$ and $MString$ split as direct sums of Morava $E$-theories after tensoring with a finite Galois extension of the sphere called $E^{hF_{3/2}}$. In the case of $MString$ we are able to refine this splitting in several ways: we show that the projection maps are determined by spin characteristic classes, that the Ando-Hopkins-Rezk orientation admits a unital section after tensoring with $E^{hF_{3/2}}$, and that the splitting can be improved to one of $E^{hH}\otimes MString$ into a direct sum of shifts of $TMF_0(3)$ where $H$ is an open subgroup of the Morava stabilizer group of index $4$.