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4 votes
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Parsing the definition of center of an algebra in a higher-categorical setting

Let us try to figure out what's happening on discrete rings, where $E_2=E_\infty$. The category $\mathrm{LMod}^{(2)}$ is, as you surmised, the category of pairs $(A,B)$ where $A$ is a commutative alge …
Denis Nardin's user avatar
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1 vote
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$K_0(\mathsf{Nil}(R))$ when $R$ is a field

The answer is yes, and this follows essentially from the Jordan decomposition of nilpotent endomorphisms. Let $(F^n,\nu)$ be an $n$-dimensional vector space and a nilpotent endomorphism. Then $\nu^n=0 …
Denis Nardin's user avatar
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16 votes
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Do Schlichting's and Balmer's definitions of higher Witt groups of a scheme agree when 2 is ...

No, the definition in Schlichting's first paper are not the "correct" definition of higher Witt groups (in any case they are not the analogue of Balmer's Witt groups), rather they are some shifted hig …
Denis Nardin's user avatar
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6 votes

Geometric Meaning of Different K-theories

Fibrant replacement is essentially sheavification with respect to the corresponding topology. So étale K-theory is nothing more than the part of K-theory that satisfies étale descent. Concretely (and …
Denis Nardin's user avatar
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21 votes
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Why does K-theory need schemes to be Noetherian?

You don't need the Noetherianness hypothesis to talk about K-theory. But the definition you propose in your question is not suited for the most general case. From a notion of K-theory we want at least …
Denis Nardin's user avatar
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22 votes
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Entering to the K-theory realm

I think that doing algebraic K-theory properly certainly requires a good background on stable homotopy theory, that is to say the homotopy theory of spectra. Unfortunately there are not many textbooks …
Denis Nardin's user avatar
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21 votes

Why presheaves with transfer?

I hope someone can provide a better answer with more of an eye towards the motivic world, but for now let me outline that the exact same phenomenon exists in classical stable homotopy theory. Here the …
Denis Nardin's user avatar
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8 votes

Good reference for topological Hochschild homology

As a first introduction I like these notes by Achim Krause and Thomas Nikolaus. They do require some familiarity with spectra and stable homotopy theory though.
Denis Nardin's user avatar
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14 votes
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Is algebraic $K$-theory a motivic spectrum?

Let me assume that $S$ is a regular Noetherian scheme (for example a field). Then algebraic K-theory is a motivic spectrum, and in fact it is represented by the $\mathbb{P}^1$-spectrum that is $BGL_\i …
Denis Nardin's user avatar
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