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Homotopy theory, homological algebra, algebraic treatments of manifolds.

5 votes

Realizing $\mathcal{A}(2)//\mathcal{A}(1)$ by a finite spectrum

As pointed out by John Rognes, this answer is not correct (it misses the $Sq^4$ from the bottom class to the class in dimension $4$). Sorry for the confusion. =========== previous answer ============ …
4 votes

Cohomology of the classifying space of $Ss(4m)$

I don't think the cohomology is known. As an indication of this I would refer to the 2007 paper "On the Stiefel–Whitney classes of the representations associated with Spin(15)" by Mamoru Mimura and Te …
Christian Nassau's user avatar
11 votes
Accepted

Adams-Novikov spectral sequence at p = 2

I don't think anybody knows how to compute this $E_2$-term efficiently (not just at the prime $2$). I would love to be proved wrong on this, of course. So far the only documented, algorithmic method …
Christian Nassau's user avatar
11 votes

Intuition behind Thom class

The idea behind the Thom isomorphism $\beta:H^iX \rightarrow H^{n+i}(DE,SE)$ is implicit in the formula $$\int_{\sigma_{n+i}} \beta(\alpha_i) = \int_{X\cap \sigma_{n+i}} \alpha_i$$ Here $\sigma_{n+i} …
Christian Nassau's user avatar
7 votes
Accepted

Image of J in the classical Adams Spectral Sequence

The image of $J$ is pretty easy to see in the Adams $E_2$ term: it consists of the elements along the vanishing line, plus, in dimensions 8k-1, of the towers that end near the vanishing line. This ide …
Christian Nassau's user avatar
12 votes

Geometric interpretation of families in the stable homotopy groups of spheres

This has been a burning question for quite some time, but not much is known. Surely, people believe that the next layer (i.e. the $\beta$-family) should also admit a geometric description, although as …
Christian Nassau's user avatar
15 votes

What are the best known results for the stable homotopy groups of spheres?

Computing $\pi_\ast(S)$ is a tedious business that to this day can only be done "by hand", i.e. by humans. The $p=2$ computation up to dimension 64 was completed by Kochman (see his SLNM book) with la …
Christian Nassau's user avatar
4 votes
Accepted

Computing squaring operations in the Adams spectral sequence

I think for $k>0$ currently no-one knows an efficient algorithmic way to compute the $Sq^k$, e.g., from a minimal resolution. (The $Sq^0$ is easy since it is induced by the "Frobenius" map on $A_\ast$ …
Christian Nassau's user avatar
3 votes

"The Z/2-cohomology functor from Top to GrVecSpaces factors through Unstable-A-Mod, and this...

My impression is that Haynes Miller uses the term "algebraic category" in the informal sense in his notes (but I may be wrong). So let me answer this informal version first: one could argue that there …
Christian Nassau's user avatar
7 votes
Accepted

Which sets of Stiefel-Whitney characteristic numbers can be realized as coming from a manifold?

The Steenrod operations on mod 2 cohomology imply the vanishing of some characteristic numbers. Specifically, if $p(w_1,w_2,\ldots)\in H^k(M^n;Z/2)$ for $k\lt n$ then $0=\langle \sum_{i+j=n-k}u_i{\rm …
Christian Nassau's user avatar
5 votes
Accepted

Morava's "Motives and cell bundles"?

Google knows about this preprint ("A theory of base motives") which seems related: http://folk.uio.no/rognes/yff/morava.pdf
Christian Nassau's user avatar