English

On the ring of cooperations for real hermitian K-theory

Algebraic Topology 2026-05-15 v3 Algebraic Geometry K-Theory and Homology

Abstract

Let kq denote the very effective cover of the motivic Hermitian K-theory spectrum. We analyze the ring of cooperations πR(kqkq)\pi^\mathbb{R}_{**}(\text{kq} \otimes \text{kq}) in the stable motivic homotopy category SH(R)\text{SH}(\mathbb{R}), giving a full description in terms of Brown--Gitler comodules. To do this, we decompose the E2E_2-page of the motivic Adams spectral sequence and show that it must collapse. The description of the E2E_2-page is accomplished by a series of algebraic Atiyah--Hirzebruch spectral sequences which converge to the summands of the E2E_2-page. Along the way, we prove a splitting result for the very effective symplectic K-theory ksp over any base field of characteristic not two.

Keywords

Cite

@article{arxiv.2506.16672,
  title  = {On the ring of cooperations for real hermitian K-theory},
  author = {Jackson Morris},
  journal= {arXiv preprint arXiv:2506.16672},
  year   = {2026}
}

Comments

65 pages, 38 figures. Comments welcome! v2: added section 8.3, other changes based on referee report. v3: Final version, to appear in Annals of K-theory. Margin size change, figures now vector files