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Student.


Oct
17
comment Topological structure of a quotient of ${\rm{SU}}(2)\times{\rm{SU}}(2)$
Not an answer, but synonyms: $\mathbb{S}^3\times \mathbb{S}^3/\mathbb{Z}_2$ is the double cover, Spin$(4)$, of SO(4).
Oct
16
comment Christoffel symbols in Differential geometry iff proof
But Christoffel symbols are objects (non-tensors) with three indices (unless you contract two of them). I.e. $$\Gamma^\alpha_{\beta\gamma}=\frac{1}{2}g^{\alpha\mu}(g_{\mu \beta,\gamma}+g_{\mu \gamma,\beta}-g_{\beta\gamma,\mu}).$$
Oct
14
suggested suggested edit on How to show that $\frac{1}{\tan(x/2)}=2 \sum_{j=1}^{\infty}\sin(jx)$ in Cesàro way/sense?
Oct
14
comment Christoffel symbols in Differential geometry iff proof
Hi! I'd like to know what does $H$ mean? where are the Christoffel symbols here?
Oct
14
comment $4 \times 4$ matrix and its inverse. Is my method ok?
I'm sure there are more modern references, but in Jackson's book on Classical Electrodynamics (chapters 11 and 12) you can find a complete physical approach (I don't think special relativity should be read as math, for it is definitely not math). By definition, $\gamma$ satisfies $\gamma^2-\beta^2\gamma^2=1$, so you can set $\phi=\cosh^{-1}\gamma$ with a sign ambiguity to be fixed by $\sinh \phi=\beta\gamma$. Then $\gamma^2-\beta^2\gamma^2=1=\cosh^2(\phi)-\sinh^2(\phi)$.
Oct
12
awarded  Promoter
Oct
12
answered $4 \times 4$ matrix and its inverse. Is my method ok?
Sep
17
awarded  Autobiographer
Aug
11
awarded  Teacher
Jun
24
asked Dixmier-Douady class: computations
Jun
23
comment Compact resolvent VS certain boundedness condition
I see. However, one doesn't have control on the boundedness of the elements in $A$. Anyway, very helpful answer.
Jun
23
accepted Compact resolvent VS certain boundedness condition
Jun
22
revised Compact resolvent VS certain boundedness condition
deleted 43 characters in body
Jun
22
revised Compact resolvent VS certain boundedness condition
Changed condition 2. from "$(D+\lambda)^{-1}$ is a compact operator for each $\lambda\notin i\mathbb{R}$"
Jun
21
awarded  Commentator
Jun
21
revised Compact resolvent VS certain boundedness condition
added 2 characters in body
Jun
21
comment Compact resolvent VS certain boundedness condition
It tries to say "$D$ has compact resolvent".
Jun
21
revised Compact resolvent VS certain boundedness condition
added 654 characters in body; edited tags; edited title
Jun
21
asked Compact resolvent VS certain boundedness condition
Jun
13
awarded  Supporter