521 reputation
25
bio website
location
age
visits member for 2 years, 7 months
seen Sep 10 at 12:20

Feb
22
awarded  Yearling
Aug
28
comment Help with spinor indices
Are you sure the Kronecker $\delta$ is not invariant? Tell me in which frame it has the usual 0 and 1 components, then. What does it look like in another frame?
Aug
27
comment Help with spinor indices
Another way to think about all of this is to use the Lie algebra isomorphism ${\rm so}(4) \simeq {\rm su}(2) \times {\rm su}(2)$ and $\alpha$ as the index on $(1/2,0)$, $\dot\alpha$ on $(0,1/2)$ and $\mu$ on $(1/2,1/2)$. Then $\sigma^\mu{}_{\alpha\dot\alpha}$ projects $(1/2,1/2) \times (1/2,0) \times (0,1/2)$ onto the trivial representation $(0,0)$.
Aug
27
comment Help with spinor indices
Try it in two parts: first you know that $\varepsilon^{\alpha\beta}$ is an invariant tensor (which is why it's admissible to use it to lower and raise indices in a meaningful way). You've given the components for $\varepsilon^{\alpha\beta}$ and $\varepsilon_{\alpha\beta}$. How about $\varepsilon^\alpha{}_\beta$? Once you have that, why not use $\varepsilon$ to raise the $\alpha$ on both sides of your final equation?
Aug
27
comment Construct a sample space $\Omega$
What have you tried?
Aug
26
comment Paradoxes without self-reference?
The subject of "it" is the quotation, i.e. the subject of that sentence. The sentence is not the quotation, that's the point. If the subject had been "this sentence", e.g., then the sentence would have been self-referencing. This is an important distinction: not every use of the word it replaces "this sentence," including in Quine's famous example above.
Aug
25
answered Paradoxes without self-reference?
Aug
25
awarded  Commentator
Aug
25
comment Find CFG for Lisp-like expressions
The computer science stack exchange may get you better results. There are two of them: cs.stackexchange.com and cstheory.stackexchange.com
Aug
24
comment Issue with a Poisson process and its jump times
Try working recursively. Can you say what is the distribution of $(T_1,T_2)|{N_t = 2}$?
Jun
5
answered derivative of exponential of matrix trace
Jun
5
comment derivative of exponential of matrix trace
You need to clarify your notation a bit. Is $C_{ij}$ a constant matrix for each pair $ij$, i.e. a family of matrices labeled by two indices, $i$ and $j$, or is $C$ a matrix with components $C_{ij}$? If the latter, then there is no additional summation over $i$ and $j$ after evaluating $e^{-{\rm tr}(X^T C X)}$.
Jun
5
answered Green's theorem and flux
Apr
2
comment Determinant of the transpose of elementary matrices
no big deal, glad you understand more now too.
Mar
20
comment Determinant of the transpose of elementary matrices
It is not true that $\det{M} = \mathrm{tr}\,M$ for upper or lower triangular matrices.
Feb
22
awarded  Yearling
Nov
5
revised How many integer solutions to a linear combination, with restrictions?
deleted 5 characters in body
Nov
5
answered How many integer solutions to a linear combination, with restrictions?
Apr
1
answered Old MIT exam question, how do I solve it?
Mar
14
suggested suggested edit on Newton-Raphson's Method to find $\sqrt{2012}$