# Search results

1. ### WMAP Cl data

I'd like to compare some models of mine against results from WMAP. Is there anywhere I can get the data, l(l+1) Cl / 2pi as a function of l? I see plenty of images of the TT, TE power spectra with error bars on them from WMAP, but can't seem to find the data. Ideally I'd like to plot my models...
2. ### How do I split equations in LaTeX

Couldn't think of a better place to post this. I'm writing a document in latex that has several very large equations in it. I can split them up so that they take up two or three lines using the \begin{split} command or \begin{align} command, but If I need to split a line that is contained within...
3. ### Rasing and lowering indicies

In GR the metric can raise or lower indices, but which index will it raise in this case: \delta^{ij} \partial_i \xi_j is it, \partial^j \xi_j or, \partial_i \xi^i Or are these equal?
4. ### Covariant derivative

just a quick query, I know that, \nabla_0 A_{\alpha}= \partial_0 A_{\alpha} - \Gamma^{\beta}_{0 \alpha} A_{\beta} But what does \nabla^0 A_{\alpha} equal?
5. ### Help computing Christoffel coefficient

Not so much a homework problem, more needing help understanding where something comes from. I've attached a jpg file with what I need help on. I've done a general relativity course at uni but can't seem to work out what should be a very simple problem.
6. ### What does 2 - 3 sigma mean?

Hi all, I'm reading some journal articles and in many of them, when they quote a result, they add 'at the 2 to 3 sigma limit.' I realise this is some sort of statistical quantity, but what exactly does it mean, and do lower values of sigma mean better results? Thanks
7. ### Relativity question

Hi all, I'm trying to teach myself relativity using Sean Carroll's lecture notes. Although this Isn't a homework question I thought this part of the forum was the best place to ask. On page 76 of http://arxiv.org/pdf/gr-qc/9712019, how have they got the first equation in (3.50) from...
8. ### Scalar field pressure and energy density

Hi all, I'm hoping someone can help me out as I'm really stuck. With reference to the top of page 7 at http://faculty.washington.edu/mrdepies/Survey_of_Dark_Energy2.pdf I'd like to know how to get the quoted energy density and pressure of phi from the stress-energy tensor. Im very new...
9. ### Classical mechaincs question

Hi all, Was given a question which went like this: Consider a closed mechanical system described by s generalized coordinates qi. How many additive integrals of motions exist for this system? I'm not quite sure exactly what is meant by this. I know that there are 2s-1 integrals for this...
10. ### Isothermal v NFW halos

Hi all, I have currently been reading up on dark matter halos as I’m considering doing a small project on them for my degree. I plan to use an (approximated) analytical equation for the density at r of an isothermal halo in terms of the halos central density and core radius. density(r) =...
11. ### I'm looking at this question:'If we assume as oscillation of form

I'm looking at this question: 'If we assume as oscillation of form y = Aexp(iwt) what is the operator w? What then is the operator for frequency f?' I have no idea what is ment by operator. I've tried looking it up in books and the net, but the explinations im finding just aint helping me...
12. ### Electron in magnetic field and TV

this isnt homework, im just doing a bit of revision before exams, and came across this problem. Not really sure where to start really. here it is: In an electron gun of a TV picture tube the electrons (charge -e, mass m) are accelerated by a voltage V. After leaving the electron gun, the...
13. ### Two positive point charges Q are held on the x-axis at x = a and at x = -a

I've been doing this question, but cant seem to get past a particular bit. heres the question: 'Two positive point charges Q are held on the x-axis at x = a and at x = -a. A third positive point charge q, of mass m, is placed on the x-axis away from the origin at coordinate x such that |x| <<...