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    • CommentRowNumber1.
    • CommentAuthorTim_Porter
    • CommentTimeAug 23rd 2011

    I have deleted an old out of date query box from homotopy theory.

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeAug 22nd 2013

    have added a pointer to the new Problems in homotopy theory Wiki

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeSep 24th 2013

    I have expanded the beginning of the list of References at homotopy theory, with brief comments (Quillen had been missing, Lurie had been missing, UF had been missing).

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeApr 12th 2017
    • (edited Apr 12th 2017)

    The Idea-section at homotopy theory had been abysmal.

    I have written something more substantial now, see here.

    This is just so that I may point from other introductory pages like Introduction to Topology to “homotopy theory” without feeling that I am sending the reader down the cliff. But I don’t actually have time to deal with bringing the entry on homotopy theory into shape right now. Everybody please feel invited to expand on that entry further.

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2018
    • (edited Apr 13th 2018)

    below the reference to Tyler Lawson’s “Homotopy theory: The future” I added pointer to Clark Barwick’s “The future of homotopy theory” (now Barwick 17).

    It seems to fit there, even though it is less about the subject of homotopy theory than about the sociology of its practitioners.

    diff, v62, current

    • CommentRowNumber6.
    • CommentAuthorDavid_Corfield
    • CommentTimeApr 13th 2018

    It would be helpful if Barwick could give some existing exemplary writings of the kind he’s looking to encourage.

    Presumably Lawson’s talk would count. Strictly, I guess it should be named ’Chromatic homotopy theory: The future’, since it came at the end of the 2013 Talbot workshop of that name.

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2018
    • (edited Apr 13th 2018)

    It’s time to finally nail down the fundamental relationship between homotopy theory and string/M theory from first principles, not relying on oracles.

    With Hisham and John H., we have finally sorted out how ADE-equivariant homotopy theory classifies intersecting black brane configurations. (It’s closely related to, but not exactly how I had imagined it in Jan 2016, instead it’s in un-stable equivariant (rational) cohomotopy, after all…).

    First we were perplexed that the G ADEG_{ADE}-equivariant enhancement of the M2/M5-cocycle, while correctly detecting the “black” M2 and M5, misses the KK6 (the “M6”) as well as the M9. But reflection reveals that the nascent equivariant homotopy theory of black branes is already smarter than we are: The isolated KK6 (in its guise as the D6) suffers from the RR-field tadpole anomaly and it is only its “M5 half-brane“-intersection with the M9 (it its guise as the O8-plane) that should appear, which turns out to be exactly the thing that the G ADEG_{ADE}-equivariant cohomology theory reports as being a non-trivial cocycle.

    • CommentRowNumber8.
    • CommentAuthorDavid_Corfield
    • CommentTimeApr 13th 2018

    How does one know about ADE gauge enhancement from “first principles”? I see from your slide 54 that one construction “happens to be the same as” a black M5-brane at an A-type singularity, but that doesn’t sound like a first principles derivation.

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2018
    • (edited Apr 13th 2018)

    You are referring to slide 54 here.

    So there is one choice of S 1S^1-action on the 4-sphere such that gauge enhancement exists in the sense of a lift as on slide 61, after fiberwise Goodwillie linearization. This is from “first principles” in that it is just a mathematical analysis of the structure inside the equivariant Whitehead tower that grows out of the super-point.

    That S 1S^1-action is, it turns out (hence “happens to be”) the A-type action on the 4-sphere, namely the one induced by regarding S 1=U(1)SU(2)=S()S^1 = U(1) \subset SU(2) = S(\mathbb{H}) and identifying S 4=S()S^4 =S(\mathbb{R} \oplus \mathbb{H}).

    Moreover, analysis shows that what makes the gauge enhancement work is the fact that the fixed point set of this action is S 0S 4S^0 \hookrightarrow S^4. But this is the case for every non-trivial subgroup of SU(2)SU(2). Restricting to finite subgroups, this yields the ADE-orbifolds of the 4-sphere.

    • CommentRowNumber10.
    • CommentAuthorDavid_Corfield
    • CommentTimeApr 13th 2018

    The power of \emptyset!

    • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeApr 13th 2018

    I suppose now you are referring to slide 83.

    • CommentRowNumber12.
    • CommentAuthorDavid_Corfield
    • CommentTimeApr 18th 2018

    Any further thoughts on expressing such work (#7) in terms of “Cartan geometry with singularities” from here?

    • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeApr 18th 2018

    I haven’t further developed “Cartan geometry with singularities” yet, but our understanding of these local models (super-Minkowski spacetimes with super-ADE-singularities) has much progressed. We should have a first version of the article to share next week.

    It turns out that the classification of these local models matches the classification of BPS-solutions to 11d supergravity, including a fair bit of fine print. This means that when working in supergeometry, the “quantum numbers” of black brane solutions to supergravity (dimension, BPS degree, singularity structure) is already fixed by a super tangent space wise analysis, hence on the local model spaces.

    This reinforces the idea that black pp-brane physics is a topic in super Cartan geometry with singularities. On a rough level it is clear how this works, but I haven’t tried to write it out as a formal theory yet.