Recent content by shadishacker

Dear all, In a recent talk, I have heard that speed of gravitational waves is non-dispersive. How is it proved "observationally" in LIGO detections that all the frequencies travel with the same speed, so one can say the speed is non-dispersive?

Hi! Can anyone tell me what the radial BAO size method is? how do people use it to get to the H(z)? I am reading the paper "Constraints on the Dark Side of the Universe and Observational Hubble Parameter Data " by Zhang et al. and I think I am lost! Can anyone tell me very simple, how they do...

Dear Bandersnatch, Sorry if I marked the level wrong. Anyway, thanks for the explanations. I get the point now.

So zero is not smack dab in the middle of the range, but it is -0.01. right? do they conclude the variation is zero because of -0.01 is a small number near 0?

Am I missing something? Isn't the middle of the range -0.01?

But how this "null result" given in this number? $\Delta \alpha/ \alpha = (-0.01\pm0.26) \times 10^{-5}$ which is for instance given in CONSTRAINING THE VARIATION OF THE FINE-STRUCTURE CONSTANT WITH OBSERVATIONS OF NARROW QUASAR ABSORPTION LINES" by Songaila et. al ? I mean, how is 0 at the...

Thanks a lot for the clear reply. I'd like to ask two other questions: - About this variation, in recent papers like " High-precision limit on variation in the fine-structure constant from a single quasar absorption system " by Kotus et. al mention that the measured variation for alpha is...

Hi everyone, I am new to observations and observational terms! I am reading the paper "constraining the time variation of the fine-structure constant" by Srianand et. al in the section "constraining alpha with QSO absorption lines" there is a sentence saying "... rest wavelengths of MG II ...

Dear Chiro, So you mean I can change the shape of the distribution to a nomal one? but is it a right thing to do? I mean if there are observational points, then doesn't this change the data completely?!

I think it means that the mean is 2. and as the distribution is normal, the \begin{equation} \mu^2=0.1\end{equation} However if the distribution is not normal, then \begin{equation} \mu^2\end{equation} would be different from left and right side of the mean.

yes, it means it can go from 1.9 to 2.9. But until now, I have used Chi squared test only for normal distributions, which are for instance: \begin{equation}f_i = 2_{0.1}^{0.1}\end{equation} i.e. error in both sides are the same.

Hi everyone. I am totally new to statistics so my question may or may not be simple! I know that for the data fitting we can do a chi squared test like: \begin{equation} \chi^2 = \Sigma \frac{(f_{data}-f_{model})^2}{(error_{data})^2}\end{equation} So I have been doing this for a while, but now...

Dear all, I am looking for observational data for the number count of galaxy mass function: \begin{equation} dn/dM\end{equation} in terms of redshift and also mass, to compare with theories. I know that I can use HIPASS data (most probably), but as I am new to the field, I have to idea: 1-...

Has anybody seen any paper on the change of Hubble parameter with f(R)? Is there at least any approximation?

I just realized that the equations consist the forth order of the scale factor (a(t)). Are these solvable in the matter dominated era? when \begin{equation} \rho(z)=\rho_m a^{-3} \end{equation}