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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeOct 28th 2009
    • (edited Dec 20th 2012)

    created motive just in order to link to the sub-pages on this that we already have, and in order to record a link to a useful MO discussion about them.

    • CommentRowNumber2.
    • CommentAuthorzskoda
    • CommentTimeOct 30th 2009
    I am glad to hear revival of interests in motives in nlab :)

    I had trouble understanding abbreviation MO in this and few other entries. Let us minimize globally uknown abbreviations; nlab already has many local technical terms which scare some potential contributors away.
    • CommentRowNumber3.
    • CommentAuthorTobyBartels
    • CommentTimeOct 30th 2009

    ‘MO’ isn't really a technical term; it referes to Math Overflow, the awesome new resource for professional mathematicians to ask and answer questions. (I sound like an ad, but it is awesome.)

    • CommentRowNumber4.
    • CommentAuthorzskoda
    • CommentTimeMar 17th 2010

    Created Nori's Tannakian theorem. New Kaledin's reference at motive.

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeDec 20th 2012
    • (edited Dec 20th 2012)

    Today I quizzed an expert on motives. Finally I got something that I could recognize as a clean formal abstract definition. I have tried to make a quick note that brings out the clean basic idea of the formal definition in a new section motive -- Idea -- Idea of the precise abstract definition.

    Experts may still complain, but to my mind this brings the entry lightyears closer to being an actual explanation of what a motive is than it was before.

    If you are an expert and still feel appalled by the sheer insufficiency of the entry, maybe the new paragraph at least serves as a condensation point for something better.

    • CommentRowNumber6.
    • CommentAuthorMike Shulman
    • CommentTimeDec 21st 2012

    Nice!

    Pushing monoidal units forwards to a point reminds me of what Kate and I did with indexed monoidal categories. Except that in algebraic-geometry land, they push forward by the right adjoint of pullback…

    • CommentRowNumber7.
    • CommentAuthorMarc Hoyois
    • CommentTimeDec 21st 2012

    I wouldn’t denote the initial functor by DM because there already exists an (,1)(\infty,1)-functor DM which is meant to be initial for a different set of axioms. The usual notation for the initial (,1)(\infty,1)-functor in the sense meant here is SH. Ideally DM would also satisfy the axioms displayed here (and more), but it’s not known to satisfy the localization property (= property 2).

    I think part 2 of the “idea of definition” is wrong: the motive of XX would be p 1 Xp_\sharp 1_X where p p_\sharp is left adjoint to p *p^\ast.

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeDec 23rd 2012

    Hi Marc,

    okay, I have changed that. What's your favorite reference that states theses definitions clearly?

    • CommentRowNumber9.
    • CommentAuthorzskoda
    • CommentTimeDec 23rd 2012

    I added the word “derived” to that section. This is the idea of derived mixed motives, not the conjectural true abelian category of mixed motives. For pure motives and Nori’s motives one works with nonderived version, but for mixed motives one has only a conjecture, no definition yet.

    • CommentRowNumber10.
    • CommentAuthorMarc Hoyois
    • CommentTimeDec 29th 2012

    @Urs: I know of no other reference than Cisinski-Déglise. They define the standard DMDM in part 3, but they are unable to prove that it satisfies the complete 6-functor formalism. In part 4 they construct a rational version DM BDM_B (should be a cyrillic B) which has the 6-functor formalism. I just quickly went through the updated introduction, and I don’t see them mentioning any universal properties of these 2-functors. However, these 2-functors have obvious “objectwise” universal properties by definition, and the objectwise universal properties together with the 6-functor formalism should be stronger than just a universal property for the 2-functor.

    For example, for a fixed base scheme SS, the functor Sm/SDM(S)Sm/S \to DM(S) is the universal functor to a cocomplete stable symmetric monoidal (,1)(\infty,1)-category which (1) has transfers, (2) satisfies Nisnevich excision, (3) is homotopy invariant, and (4) inverts the Tate object. The rational version DM B(S)DM_B(S) satisfies the same universal property with \mathbb{Q}-coefficients and with Nisnevich excision replaced by étale hyperdescent (transfers are then redundant), and various other universal properties if we add regularity assumptions on SS.

    • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeDec 29th 2012
    • (edited Dec 29th 2012)

    I know of no other reference than Cisinski-Déglise.

    Thanks, I see. What about those lecture notes allegedly taken by Deligne of a lecture by Voevodsky, where the idea of these axioms supposedly originates? The article points to Voevodsky’s general IAS web page, which, however, seems to have no trace of a pointer to such notes left (?)

    • CommentRowNumber12.
    • CommentAuthorMarc Hoyois
    • CommentTimeDec 30th 2012

    You probably mean these notes. They are superseded by Ayoub’s thesis, but neither of them say anything about DM. Well, they both make it seem as though DM is known to satisfy the axioms (at the very end in Deligne’s notes), but it’s not. As far as I know Cisinski-Déglise has the complete story about DM (and most of it is in the introduction).

    • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeDec 30th 2012

    You probably mean these notes.

    Yes, thanks! I have added that to motive.

    They are superseded by Ayoub’s thesis, but neither of them say anything about DM. Well, they both make it seem as though DM is known to satisfy the axioms (at the very end in Deligne’s notes), but it’s not. As far as I know Cisinski-Déglise has the complete story about DM (and most of it is in the introduction).

    Thanks. That’s all very useful to know.

    • CommentRowNumber14.
    • CommentAuthorMarc Hoyois
    • CommentTimeJul 22nd 2013

    I added a whole bunch of modern constructions of the derived category of mixed motives.

    I’ve still got a beef with the Idea of the precise abstract definition of derived motives, however. It seems that this section was written under the idea that stable motivic homotopy theory deserves to be called the “derived category of motives”. This is certainly not the case, as all the definitions of the latter that I’ve added should make clear. The analogy is

    • stable motivic homotopy theory \leftrightarrow stable homotopy theory

    • derived motives \leftrightarrow chain complexes

    (however, the vertical relationship on the LHS is more complicated than on the RHS, even with rational coefficients – see the definition of “Morel motive”).

    I suggest moving the content of this section to stable motivic homotopy theory under “six operations”.

    • CommentRowNumber15.
    • CommentAuthorMarc Hoyois
    • CommentTimeJul 24th 2013

    I suggest moving the content of this section to stable motivic homotopy theory under “six operations”.

    I went ahead and did that: six operations.

    • CommentRowNumber16.
    • CommentAuthorUrs
    • CommentTimeAug 11th 2013

    I have added to motive in the (References-)section on relation to physics the following:


    That the pull-push quantization in Gromov-Witten theory is naturally understood as a “motivic quantization” in terms of Chow motives of Deligne-Mumford stacks was suggested in

    Further investigation of these stacky Chow motives then appears in

    • CommentRowNumber17.
    • CommentAuthorMarc Hoyois
    • CommentTimeAug 12th 2013

    I added a brief paragraph about Deligne’s Tannakian category of mixed motives, with a reference.

    • CommentRowNumber18.
    • CommentAuthoradeelkh
    • CommentTimeJan 28th 2014
    • (edited Jan 28th 2014)

    Started writing the construction of DM, following Cisinski-Déglise, at

    I’ve got up to DM^{eff} for the moment, I think I will add some prerequisites on model structures on spectra, following Ayoub’s thesis, before I do DM.

    Also I created

    following Déglise.

    • CommentRowNumber19.
    • CommentAuthorUrs
    • CommentTimeJan 29th 2014

    Thanks!

    At some point we may want to merge various things. We have related discussion at motivic homotopy theory and at motive, and maybe elsewhere, too. I am not sure.

    • CommentRowNumber20.
    • CommentAuthoradeelkh
    • CommentTimeJan 29th 2014

    I think what is at motivic homotopy theory is related but different. I hadn’t seen the constructions at motive though, they should probably also be moved to mixed motive.

    • CommentRowNumber21.
    • CommentAuthoradeelkh
    • CommentTimeJan 29th 2014
    • (edited Jan 30th 2014)

    I created symmetric sequence and added a general definition at spectrum, following Ayoub’s thesis.

    Next is monoidal and model structures on spectra.

    edit: there is some stuff on the symmetric monoidal structures now.

    • CommentRowNumber22.
    • CommentAuthorzskoda
    • CommentTimeJul 23rd 2015

    I added today’s Caramello’s paper on motives from the topos point of view into motive entry. I also merged the references section with lost subsection a page above also containing and named as “references”. That was somehow lost in organization of the page. The merger may need further microorganization (the moved references are still under “general”, only one reference was double listed).

    • CommentRowNumber23.
    • CommentAuthorspitters
    • CommentTimeJul 24th 2015

    I have only glanced at Olivia’s paper. Is my impression correct that this motivation is different from the one stated in cohomology#ToposTheory ?

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