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Non-commutative rings and algebras, non-associative algebras. Can be used in combination with ra.rings-and-algebras

13 votes
2 answers
719 views

Ideals in Factors

One can easily prove that factors have no nontrivial ultraweakly closed 2-sided ideals as these are equivalent to nontrivial central projections. One can also show type $I_n$, type $II_1$, and type $I …
Dave Penneys's user avatar
  • 5,425
14 votes
9 answers
2k views

Examples of noncommutative analogs outside operator algebras?

Theo's question made me wonder if there are other "noncommutative analogs" outside of operator algebras. Some noncommutative analogs from operator algebras include: A $C^\ast$-algebra is a noncommut …
Dave Penneys's user avatar
  • 5,425
9 votes
7 answers
2k views

Hochschild/cyclic homology of von Neumann algebras: useless?

Hochschild homology gives invariants of (unital) $k$-algebras for $k$ a unital, commutative ring. If we let our algebra $A$ be the group ring $k[G]$ for $G$ a finite group, we get group homology. Ther …
Dave Penneys's user avatar
  • 5,425
14 votes
2 answers
882 views

Do torsion-free groups give projectionless group ($C^\ast$) algebras?

One of the reasons I study von Neumann algebras is that they always have plenty of projections. There are many projectionless $C^\ast$-algebras ($0$ and possibly $1$ are the only projections), but the …
Dave Penneys's user avatar
  • 5,425