13,235 reputation
4376
bio website wwwmath.uni-muenster.de/…
location Münster
age 38
visits member for 4 years, 7 months
seen May 20 at 7:34

I am a mathematician based in Münster, Germany. A fellow MO user once described me as a ''very homotopy-theoretic geometric topologist'' and I largely approve this description.


Apr
13
awarded  Nice Answer
Feb
17
revised Homotopy spheres with vanishing and non-vanishing $\alpha$-invariant
added 444 characters in body
Feb
6
awarded  Nice Answer
Feb
4
awarded  Necromancer
Jan
7
answered The periodic values in Bott periodicity
Jan
7
answered How to show the square root function of a positive semidefinite matrix is differentiable?
Jan
5
revised Homotopy spheres with vanishing and non-vanishing $\alpha$-invariant
added 3 characters in body
Dec
13
answered Equation for non-invertible elements in Clifford algebras
Dec
2
comment Local index formula for >ungraded< elliptic operators
Typically, you would replace the operator $P$ by $P \oplus P^{\ast}: E \oplus F \to E \oplus F$. This is graded, and the index (in the graded sense) is the usual index. An ungraded operator has an index in $K^1$, but only if it is self-adjoint.
Nov
26
comment Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
I think I agree. What I did not realize was that $F$ is obtained from $(x/2)/\sinh(x/2)$ by a simple scaling in the argument. In that case, the components of the multiplicative seqeunce of $F$ are obtained from the components of the A-hat-genus by multiplication with constants.
Nov
24
awarded  Favorite Question
Nov
20
awarded  Enlightened
Nov
20
awarded  Nice Answer
Nov
20
comment Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
yes, the formula has a typo in it.
Nov
19
comment Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
@Juan: I could have guessed. I came across the paper, but did not understand what is going on. Can you tell me what the index theoretic significance of the Mayer class is?
Nov
19
answered Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
Nov
19
comment Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
And where does the Mayer class come from? I am just curious.
Nov
19
comment Is true that $\left[\frac{\hat{A}(\mathbb HP^m)} { \hat{M}(\mathbb HP^m) }\right]_{4m} = 0$?
What is the Mayer class? I have never heard about it.
Oct
30
comment What are the “correct” conventions for defining Clifford algebras?
@Qiaochu: then I recommend to take the tangent bundle. Another situation where one (e.g. me this week) has to be more careful is when you scale metrics by positive functions $f:M \to R$.
Oct
29
comment What are the “correct” conventions for defining Clifford algebras?
It is almost totally irrelevant whether you take tangent or cotangent bundles; all the theory is for Riemann manifolds, where both are naturally isomorphic.