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Tuesday, September 18, 2018

**Abstract:** It is a classical result that the rational homotopy groups, $\pi_*(X)\otimes \mathbb{Q}$, as a Lie-algebra can be computed in terms of indecomposable elements of the rational cochains on $X$. The closest we can get to a similar statement for general homotopy groups is the Goodwillie spectral sequence, which computes the homotopy group of a space from its "spectral Lie algebra". Unfortunately both input and differentials are hard to get at. We therefore simplify the homotopy groups by taking the unstable $\nu_h$-periodic homotopy groups, $\nu_h^{-1}\pi_*(\ )$ (note $h=0$ recovers rational homotopy groups). For $h=1$ we are able to compute the $K$-theory based $\nu_1$-periodic Goodwillie spectral sequence in terms of derived indecomposables. This allows us to compute $\nu_1^{-1}\pi_*SU(d)$ in a very different way from the original computation by Davis.

Friday, September 21, 2018