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I am studying the case of infinitesimal proper Lorentz transformations, and I stumble at this notation result : $\Delta\omega^\alpha_\gamma g_{\alpha\beta} g^\beta_\delta = \Delta \omega_{\delta\gamma}$?

I know that the following is true : $x^\mu = g^{\mu\sigma} x_\sigma$. So what happens here is that the metric tensor raises the index and then the raised index changes to the Greek letter which is not contracted, μ in this case. How does the same applies in the above equation which I cannot understand ?

Edit : Prahar was correct I had made a mistake. I solved it and this is how :

$g_{\alpha\beta} g^\beta_\delta = g_{\alpha\delta}$

$\Delta\omega^\alpha_\gamma\cdot g_{\alpha\delta}=\Delta\omega_{\delta\gamma}$

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  • $\begingroup$ It is very confusing as it is currently written. Please use Latex for the subscripts, etc... $\endgroup$ Commented Jan 6, 2021 at 14:32
  • $\begingroup$ and then how can i display it here from latex? $\endgroup$
    – imbAF
    Commented Jan 6, 2021 at 14:34
  • $\begingroup$ I added LaTeX to your equations exactly as you had written it out without making any other changes. As they currently stand (v2) - the equations make no sense but I left it as you wrote them in the hope that it will help you understand why it's wrong and how to correct it. $\endgroup$
    – Prahar
    Commented Jan 6, 2021 at 14:37
  • $\begingroup$ This are from my professors note. he said actually (for the first equation) alpha goes down and becomes gamma and beta goes down and it becomes delta. First of all from where i am supposed to know that one metric can be used by both elements, and the rule is not even right,because the example i give down contradicts what he said.When the index changes up or down the letter representing the index changes to the one close to the metric tensor which is no contracted. $\endgroup$
    – imbAF
    Commented Jan 6, 2021 at 14:42

1 Answer 1

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First, I think that $g^{\beta}_{\delta}$ notation should be changed to $\delta^{\beta}_{\delta}$, representing the Kronecker symbol, which by definition is equal to 1 if $\beta=\delta$ and equal to 0 if $\beta\neq\delta$. So, the equation reduces to the case when $\beta=\delta$ and thus we have $\Delta\omega^{\alpha}_{\gamma} g_{\alpha\delta}$ which is then equal to $\Delta\omega_{\delta\gamma}$ by the transformation you are given. I hope this helps.

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  • $\begingroup$ I solved it! But it is good to know another way how to, thanks $\endgroup$
    – imbAF
    Commented Jan 6, 2021 at 15:05

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